;===================================================================================================
;                  Super PC/Turbo XT BIOS for Intel 8088 or NEC "V20" Motherboards
;           Additions by Ya`akov Miles (1987) and Jon Petrosky <Plasma> (2008, 2011-2012)
;                                     http://www.phatcode.net/
;---------------------------------------------------------------------------------------------------
; This is a modification of the widely-distributed "(c) Anonymous Generic Turbo XT Anonymous" BIOS,
; which is actually a Taiwanese BIOS that was reverse-engineered by Ya`akov Miles in 1987.
;
; Back in 2008 I put together an XT system and wanted a BIOS that supported booting from a hard
; drive. The Generic XT BIOS did not support this, but since source code was provided it was easy to
; add this feature. While I was at it, I fixed some bugs I found, added more features, and cleaned
; up the code. Initially I only modified this BIOS for my computer, but I decided I might as well
; release my new version in case it proves useful for someone else.
;
; In 2011 I was informed that this BIOS did not work correctly with the original IBM PC (5150). I
; made some additional changes and now the 5150 is supported as well as the 5160 (XT) and just about
; all PC/XT clones.
;
; You do not need to have a turbo motherboard to use this BIOS, but if you do, then you can use the
; "CTRL ALT -" key combination to toggle the computer speed between fast and slow. When the speed is
; toggled, the PC speaker will sound a high/low pitched blip to indicate the system speed selected.
;---------------------------------------------------------------------------------------------------
;    File: PCXTBIOS.ASM
; Updated: v2.5 05-02-2012
;          v2.4 04-23-2012
;          v2.3 03-13-2012
;          v2.2 03-05-2012
;          v2.1 12-03-2011
;          v2.0 04-23-2008
;===================================================================================================


;---------------------------------------------------------------------------------------------------
; BIOS Configuration Definitions
;---------------------------------------------------------------------------------------------------
;IBM_PC		= 1		; Define if using with original IBM PC (5150) or exact clone
				;   This will read the 5150 config switches correctly
				;   and set the BIOS computer type to FFh (PC) rather than FEh (XT).
				;   You should also disable the TURBO_ENABLED, TURBO_BOOT, and
				;   SLOW_FLOPPY definitions if using with an original PC.

TURBO_ENABLED	= 1		; Define to enable "turbo" support and CTRL ALT - hotkey
TURBO_BOOT	= 1		; Define to boot up in "turbo" mode (full speed)
;SLOW_FLOPPY	= 1		; Define to always run floppy drive at 4.77 MHz (turbo PCs only)

;TEST_CPU	= 1		; Define to test CPU at power on
				;   If enabled, ENHANCED_KEYB must be disabled due to memory limits

TEST_VIDEO	= 1		; Define to test video memory at power on (Mono/Herc/CGA only)
				;   If enabled, CLEAR_UMA must be disabled due to memory limits

MAX_MEMORY	= 640		; Maximum conventional memory allowed in KB (with EGA/VGA)
;MAX_MEMORY	= 704		; (with Mono/Hercules)
;MAX_MEMORY	= 736		; (with CGA)

;FAST_MEM_CHECK	= 1		; Define to use faster but less thorough memory check
;NO_MEM_CHECK	= 1		; Define to clear memory only

;CLEAR_UMA	= 1		; Define to clear specifed upper memory area (UMA_START to UMA_END)
				;   If enabled, TEST_VIDEO must be disabled due to memory limits
;UMA_START	= 0D000h	; UMA region start segment, must be 8K aligned
;UMA_END 	= 0F000h	; UMA region end segment, must be 8K aligned

ENHANCED_KEYB	= 1		; Define for Int 9h enhanced (101-key) keyboard support
				;   If enabled, TEST_CPU must be disabled due to memory limits

BOOT_DELAY	= 3		; Number of seconds to wait after memory test (keypress will bypass)

;WARM_BOOT_BASIC = 1		; Define to display ROM BASIC boot prompt during a warm boot


;---------------------------------------------------------------------------------------------------
; System Error Codes (may be combined)
;---------------------------------------------------------------------------------------------------
error_bios	equ	01h		; Bad ROM BIOS checksum, patch last byte
error_ram	equ	02h		; Bad RAM in main memory, replace
error_video	equ	04h		; Bad RAM in video card, replace
error_mem	equ	10h		; Bad RAM in vector area, replace
error_rom	equ	20h		; Bad ROM in expansion area, bad checksum


;---------------------------------------------------------------------------------------------------
; Changes by Plasma
;---------------------------------------------------------------------------------------------------
; Version 2.5 Changes:
;
; Added:
;  * Option to clear user-defined memory region in upper memory area (UMA) for systems with non-EMS
;    UMBs. These UMBs should be cleared before use or parity errors may occur. Define CLEAR_UMA and
;    set the region with UMA_START and UMA_END. Because of ROM space limitations, TEST_VIDEO must be
;    disabled if using CLEAR_UMA.
;  * Option to display ROM BASIC boot prompt during warm boot (define WARM_BOOT_BASIC).
;
; Version 2.4 Changes:
;
; Added:
;  * Improved support for 101-key enhanced keyboards (define ENHANCED_KEYB to enable)
;  * CPU test now optional (define TEST_CPU). Must be disabled if ENHANCED_KEYB is enabled due to
;    ROM space limitations.
;  * Video memory test now optional (define TEST_VIDEO). Applies only to Mono/Herc/CGA cards; video
;    memory is never tested on EGA/VGA cards.
;
; Changed:
;  * Int 16h extended keyboard functions now fully implemented (ah=00h/01h/02h/05h/10h/11h/12h).
;    Note that ENHANCED_KEYB does not need to be enabled to use these functions.
;  * KEYB_SHIFT_FIX removed; use ENHANCED_KEYB instead.
;  * NO_MEM_CHECK now faster; only zeroes out memory and does not blank check.
;  * Removed Int 15h hooks for future expansion BIOS (not used)
;
; Version 2.3 Changes:
;
; Changed:
;  * Int 16h extended keyboard functions (ah=10h/11h/12h) now mapped to standard functions
;    (ah=00h/01h/02h) for programs that expect enhanced keyboard support.
;
; Version 2.2 Changes:
;
; Added:
;  * Make batch file generates proper 32K ROMs for IBM 5155 and 5160
;
; Bug Fixed/Changed:
;   * FAST_MEM_CHECK option now clears memory after testing. This fixes problems with programs
;     unable to find free interrupt vectors. However the "fast" memory check is now slower. For the
;     fastest startup you can now disable the memory check with the NO_MEM_CHECK option.
; 
; Version 2.1 Changes:
; 
; Added:
;   * Optional define for IBM PC 5150 support (config switches on motherboard are read differently)
;   * Original IBM PC 5150 Int 2 (NMI) entry point now supported for better IBM PC compatibility
;   * Optional define to disable turbo support completely (for non-turbo 4.77 MHz systems)
;   * Int 15h hooks are called for future expansion BIOS to display drives and boot menu if present
;   * Optional define to set boot delay length
;
; Changed:
;   * Hard drive boot sector load is now only attempted 2 times rather than 4
;   * Boot delay now based on system timer rather than fixed loops, useful for very fast systems
;   * Pressing any key during boot delay message will end delay and start booting
;
; Bug Fixes:
;   * Boots to BASIC if no floppy or hard drive controller (previously would hang)
;   * Screen cleared after error if user chooses to continue booting
;
; Version 2.0 Changes:
;
; Code:
;   * Changed from MASM 4.x to TASM IDEAL mode
;   * Cleaned up source code: added procs, more descriptive labels
;     (...still some spaghetti due to necessary hard-coded entry points)
;
; Bug Fixes:
;   * Warm boot flag restored after external ROM initialization code (fixes CTRL+ALT+DEL warm boot)
;   * Equipment Flag in BIOS Data Area now set correctly
;   * Fixed cursor shape when using Hercules card (was in the middle of the character)
;
; Added:
;   * Optional define to always boot up in turbo mode (TURBO_BOOT)
;   * Optional define for fast memory check (FAST_MEM_CHECK); uses one test pattern only
;   * Optional define for 101-key keyboard shift+nav keys work-around (KEYB_SHIFT_FIX)
;   * BIOS is now EGA/VGA aware; will only test video memory on Mono/Herc/CGA cards
;   * Nicer boot screen with color support for CGA/EGA/VGA
;   * Processor and Math Coprocessor detection
;   * Memory test displays count every 8K; speeds up check on fast systems with slow video cards
;   * User has option to boot ROM BASIC even if bootable disk present
;   * Supports booting from hard drive (if external controller ROM present)
;   * Toggling turbo on/off sounds high/low-pitched beep rather than changing cursor shape
;
; Notes:
;   * High-density floppy disks (3.5" 1.44MB and 5.25" 1.2MB) are not supported due to lack of
;     ROM space. You will need to use an external floppy controller BIOS for this. Another option
;     is to run DR-DOS, which loads software support for high-density drives (this still requires a
;     high-density controller, but no ROM required). There is also a DOS TSR called "2M-XBIOS" which
;     adds this support to any DOS, but you cannot boot from a high-density disk.
;
;   * Cassette functions are not supported, also due to lack of ROM space. This only affects IBM PC
;     5150s or exact clones since XTs do not have a cassette port.
;---------------------------------------------------------------------------------------------------


;---------------------------------------------------------------------------------------------------
; BIOS History from Ya`akov Miles
;---------------------------------------------------------------------------------------------------
; From: Ya`akov Miles <multi%dac.triumf.cdn%ubc.csnet at RELAY.CS.NET>
; To:   Info-IBMPC at MIT-MC
; Re:   BIOS Musings
;
; You may be interested in a history of where     similar source code, although this seems
; this BIOS came from, and how it arrived in      unlikely.
; its present form. A heavily patched,
; partially-functionally BIOS (with no            In any case, as evidenced by DEBUG, some of
; copyright statement, or other visible           these name-brand BIOS were full of machine-
; indication of origin) was supplied with my      level patches--did the vendor ever bother to
; IBM-PC/XT compatible 10 MHz motherboard.        reassemble and optimize the source code? The
;                                                 code that I examined was full of recursive
; In order to get my motherboard to function      INT(errupt) instructions, which did not to
; correctly, in other words, to work with the     contribute to screaming fast BIOS. Therefore,
; parity interrupt enabled and to operate         the assembly code was rearranged so as to
; with the NEC "V20", it was necessary to         eliminate some of the unnecessary CALL, JMP,
; disassemble and thoroughly go through this      and especially INT instructions, as the
; "anonymous" BIOS, which was hinted as           optimization proceeded with the later releases.
; supplied by Taiwan, while limping along on
; a name brand BIOS, as supplied on my            The BIOS is copyright (c) Anonymous, because there
; previous motherboard by a different vendor.     was no indication of the original authors...
;
; In the course of this disassembly, aided by     ps: While playing around with my 10 MHz
; comparison with the published IBM-PC/XT             motherboard, I encountered an unusual program
; listings, it became apparent that the               called HELPME.COM, which ran at a higher
; synchronization on horizontal retrace in            pitch than normal. Since this program behaved
; the video INT 10h service was the root              normally on other (8 MHz) turbo motherboards,
; cause of the failure to operate with the            my curiosity was aroused. This eventually
; NEC "V20", and that correcting it to                led me to discover that the 10 MHz
; correspond with logic (as in IBM's BIOS)            motherboard was refreshed in hardware by
; caused the glitch to disappear. I am unable         channel 1 of the 8253 timer IC, and that this
; to account as to why several name brand             channel appeared to be counting down from an
; BIOS brands (excluding IBM's) had similar           unusually fast oscillator. Maybe this could
; glitches--maybe they were produced from             cause problems with other programs...
;---------------------------------------------------------------------------------------------------


;---------------------------------------------------------------------------------------------------
; Email Header from Original BIOS
;---------------------------------------------------------------------------------------------------
; Date:     Wed, 13 Jan 88 04:26 PST
; From:     <MULTI%TRIUMFCL.BITNET@CUNYVM.CUNY.EDU>
; Subject:  BIOS.ASM update INFO-IBMPC librarys
; To:       hicks@walker-emh.arpa
;---------------------------------------------------------------------------------------------------


ideal
p8086
model	tiny
warn
multerrs


;---------------------------------------------------------------------------------------------------
; Macros
;---------------------------------------------------------------------------------------------------
; Pad code to create entry point at specified address
macro	entry	addr
	pad = str_banner - $ + addr - 0E000h
	if pad lt 0
		err	'No room for ENTRY point'
	endif
	if pad gt 0
		db	pad dup(0FFh)
	endif
endm

; Force far jump
macro	jmpf	segm, offs
	db	0EAh;
	dw	offs, segm
endm

; Line feed and carriage return
LF	equ	0Ah
CR	equ	0Dh


;---------------------------------------------------------------------------------------------------
; BIOS Data Area (BDA)
;---------------------------------------------------------------------------------------------------
assume	ds:code, ss:code, cs:code, es:code
segment	data at 40h				; IBM compatible data structure

	dw	4 dup(?)	; 40:00		; RS232 serial COM ports - up to four
	dw	4 dup(?)	; 40:08		; Parallel LPT ports - up to four
	dw	?		; 40:10		; Equipment present word
						;   Bits 15-14: Number of parallel ports
						;     00b = 1 parallel port
						;     01b = 2 parallel ports
						;     10b = 3 parallel ports
						;   Bit 13: Reserved
						;   Bit 12: Game port adapter
						;     0b = not installed
						;     1b = installed
						;   Bits 11-9: Number of serial ports
						;     000b = none
						;     001b = 1 serial port
						;     010b = 2 serial ports
						;     011b = 3 serial ports
						;     100b = 4 serial ports
						;   Bit 8: Reserved
						;   Bits 7-6: Number of floppy drives
						;     00b = 1 floppy drive
						;     01b = 2 floppy drives
						;     10b = 3 floppy drives
						;     11b = 4 floppy drives
						;   Bits 5-4: Initial video mode
						;     00b = EGA/VGA
						;     01b = color 40x25
						;     10b = color 80x25
						;     11b = monochrome 80x25
						;   Bit 3-2: System board RAM
						;     00b = 16K
						;     01b = 32K
						;     10b = 48K
						;     11b = 64K (default)
						;   Bit 1: Math coprocessor
						;     0b = not installed
						;     1b = installed
						;   Bit 0: Boot floppy
						;     0b = not installed
						;     1b = installed
	db	?		; 40:12		; MFG test flags, unused by us
	dw	?		; 40:13		; Memory size, kilobytes
	db	?		; 40:15		; IPL errors<-table/scratchpad
	db	?				;  ...unused

;------------------------------------------------ Keyboard Data Area

	db	?, ?		; 40:17		; Shift/Alt/etc. keyboard flags
	db	?		; 40:19		; Alt-KEYPAD char. goes here
	dw	?		; 40:1A		;  --> keyboard buffer head
	dw	?		; 40:1C		;  --> keyboard buffer tail
	dw	16 dup(?)	; 40:1E		; Keyboard Buffer (Scan,Value)

;------------------------------------------------ Diskette Data Area

	db	?		; 40:3E		; Drive Calibration bits 0 - 3
	db	?		; 40:3F		; Drive Motor(s) on 0-3,7=write
	db	?		; 40:40		; Ticks (18/sec) til motor off
	db	?		; 40:41		; Floppy return code stat byte
						;  1 = bad IC 765 command request
						;  2 = address mark not found
						;  3 = write to protected disk
						;  4 = sector not found
						;  8 = data late (DMA overrun)
						;  9 = DMA failed 64K page end
						; 16 = bad CRC on floppy read
						; 32 = bad NEC 765 controller
						; 64 = seek operation failed
						;128 = disk drive timed out
	db	7 dup(?)	; 40:42		; Status bytes from NEC 765

;------------------------------------------------ Video Display Area

	db	?		; 40:49		; Current CRT mode  (software)
						;  0 = 40 x 25 text (no color)
						;  1 = 40 x 25 text (16 color)
						;  2 = 80 x 25 text (no color)
						;  3 = 80 x 25 text (16 color)
						;  4 = 320 x 200 graphics 4 color
						;  5 = 320 x 200 graphics 0 color
						;  6 = 640 x 200 graphics 0 color
						;  7 = 80 x 25 text (mono card)
	dw	?		; 40:4A		; Columns on CRT screen
	dw	?		; 40:4C		; Bytes in the regen region
	dw	?		; 40:4E		; Byte offset in regen region
	dw	8 dup(?)	; 40:50		; Cursor pos for up to 8 pages
	dw	?		; 40:60		; Current cursor mode setting
	db	?		; 40:62		; Current page on display
	dw	?		; 40:63		; Base addres (B000h or B800h)
	db	?		; 40:65		; IC 6845 mode register (hardware)
	db	?		; 40:66		; Current CGA palette

;------------------------------------------------ Used to setup ROM

	dw	?, ?		; 40:67		; Eprom base Offset,Segment
	db	?		; 40:6B		; Last spurious interrupt IRQ

;------------------------------------------------ Timer Data Area

	dw	?		; 40:6C		; Ticks since midnite (lo)
	dw	?		; 40:6E		; Ticks since midnite (hi)
	db	?		; 40:70		; Non-zero if new day

;------------------------------------------------ System Data Area

	db	?		; 40:71		; Sign bit set iff break
	dw	?		; 40:72		; Warm boot iff 1234h value

;------------------------------------------------ Hard Disk Scratchpad
	dw	?, ?		; 40:74

;------------------------------------------------ Timout Areas/PRT/LPT

	db	4 dup(?)	; 40:78		; Ticks for LPT 1-4 timeouts
	db	4 dup(?)	; 40:7C		; Ticks for COM 1-4 timeouts

;------------------------------------------------ Keyboard Buffer Start/End

	dw	?		; 40:80		; Contains 1Eh, buffer start
	dw	?		; 40:82		; Contains 3Eh, buffer end

ends	data


;---------------------------------------------------------------------------------------------------
; Segment Definitions
;---------------------------------------------------------------------------------------------------
segment	dos_dir at 50h				; Boot disk directory from IPL

label	copy	byte				;   0 if Print Screen idle
						;   1 if PrtScr copying screen
						; 255 if PrtScr error in copy
						;   (non-graphics PrtScr in BIOS)

	db	200h dup(?)			; PC-DOS bootstrap procedure
						;   IBMBIO.COM buffers the directory of the boot
						;   device here at IPL time when locating the guts
						;   of the operating system (IBMDOS.COM/MSDOS.SYS)
ends	dos_dir


segment	dos_seg at 70h				; "Kernel" of DOS

	; IBMBIO.COM (or IO.SYS) file loaded by boot block. Device Drivers/Bootstrap.
	; IBMDOS.COM (or MSDOS.SYS) operating system kernel immediately follows IBMBIO.COM and
	; doesn't have to be contiguous. The DOS kernel binary image is loaded by transient code
	; in the IBMBIO binary image.

ends	dos_seg


segment	ipl_seg at 0h				; Segment for boot block

	; The following boot block is loaded with 512 bytes of the first sector of the bootable
	; device by code resident in the ROM BIOS. Control is then transferred to the first word
	; 0000:7C00 of the disk-resident bootstrap.

	org	07C00h				;  Offset for boot block
boot	db	200h dup(?)			;  Start disk resident boot

ends	ipl_seg


;---------------------------------------------------------------------------------------------------
; ROM BIOS
;---------------------------------------------------------------------------------------------------
segment	code

	org	0E000h				; 8K ROM BIOS starts at F000:E000


ifdef	IBM_PC
ifdef	TURBO_ENABLED
	str_banner	db	'Turbo PC BIOS v2.5 for 8088/V20', 0
else
	str_banner	db	'Super PC BIOS v2.5 for 8088/V20', 0
endif
else
ifdef	TURBO_ENABLED
	str_banner	db	'Turbo XT BIOS v2.5 for 8088/V20', 0
else
	str_banner	db	'Super XT BIOS v2.5 for 8088/V20', 0
endif
endif
str_banner_end:

str_ega_vga	db	195, ' EGA/VGA Graphics', 0
str_parallel	db	195, ' Parallel Port at ', 0
str_game	db	195, ' Game Port at 201h', 0


;---------------------------------------------------------------------------------------------------
; BIOS Power-On Self Test (POST)
;---------------------------------------------------------------------------------------------------
	entry	0E05Bh				; IBM restart entry point
proc	post	near

cold_boot:
	mov	ax, 40h 			; Entered by POWER_ON/RESET
	mov	ds, ax
	mov	[word ds:72h], 0		; Show data areas not init

warm_boot:
	cli					; Disable interrupts
ifdef	TEST_CPU
	jmp	cpu_test			; Test CPU
endif

cpu_ok:
	cld
	mov	al, 0				; Prepare to initialize
	out	0A0h, al			;   no NMI interrupts
	mov	dx, 3D8h			; Load Color Graphic port
	out	dx, al				;   no video display
	mov	dx, 3B8h			; Load Monochrome port
	inc	al				;   no video display
	out	dx, al				;   write it out
	mov	al, 10011001b			; Program 8255 PIA chip
	out	63h, al 			;   Ports A & C, inputs
ifdef	TURBO_ENABLED
	mov	al, 10100101b			; Set (non)turbo mode
	out	61h, al 			;   on main board
endif
	mov	al, 01010100b			; IC 8253 inits memory refresh
	out	43h, al 			;   chan 1 pulses IC 8237 to
	mov	al, 12h 			;   DMA every 12h clock ticks
	out	41h, al 			;   64K done in 1 millisecond
	mov	al, 01000000b			; Latch value 12h in 8253 clock
	out	43h, al 			;   chip channel 1 counter

@@init_dma:
	mov	al, 0				; Do some initialization
	out	81h, al 			;   DMA page reg, chan 2
	out	82h, al 			;   DMA page reg, chan 3
	out	83h, al 			;   DMA page reg, chan 0,1
	out	0Dh, al 			; Stop DMA on 8237 chip
	mov	al, 01011000b			; Refresh auto-init dummy read
	out	0Bh, al 			;   on channel 0 of DMA chip
	mov	al, 01000001b			; Block verify
	out	0Bh, al 			;   on channel 1 of DMA chip
	mov	al, 01000010b			; Block verify
	out	0Bh, al 			;   on channel 2 of DMA chip
	mov	al, 01000011b			; Block verify
	out	0Bh, al 			;   on channel 3 of DMA chip
	mov	al, 0FFh			; Refresh byte count
	out	1, al				;   send lo order
	out	1, al				;   send hi order
	mov	al, 0				; Initialize 8237 command reg
	out	8, al				;   with zero
	out	0Ah, al 			; Enable DMA on all channels
	mov	al, 00110110b			; Set up 8253 timer chip
	out	43h, al 			;   chan 0 is time of day
	mov	al, 0				; Request a divide by
	out	40h, al 			;   65536 decimal
	out	40h, al 			;   0000h or 18.2 tick/sec
	mov	dx, 213h			; Expansion unit port
	mov	al, 1				;   enable it
	out	dx, al				;   do the enable
	mov	ax, 40h 			; Get BIOS data area segment
	mov	ds, ax				;   into ds register
	mov	si, [ds:72h]			; Save reset flag in si reg
	xor	ax, ax				;   cause memory check
	mov	bp, ax				;   will clobber the flag
	mov	bx, ax				; Start at segment 0000h
	mov	dx, 55AAh			;   get pattern
	cld					; Strings auto-increment

@@find_mem_size:
	xor	di, di				; Location XXXX:0
	mov	es, bx				;   load segment
	mov	[es:di], dx			;   write pattern
	cmp	dx, [es:di]			;   compare
	jnz	@@done_mem_size			;   failed, memory end
	mov	cx, 2000h			; Else zero 16 kilobytes
	repz	stosw				;   with instruction
	add	bh, 4				;   get next 16K bytes
ifdef	MAX_MEMORY
	cmp	bh, MAX_MEMORY shr 2		; Found max legal user ram?
else
	cmp	bh, 0A0h			; Found max legal IBM ram?
endif
	jb	@@find_mem_size			;   no, then check more

@@done_mem_size:
	xor	ax, ax
	mov	es, ax				; es = vector segment
	mov	ax, 80h
	mov	ss, ax				; Set up temporary stack at
	mov	sp, 100h			;   0080:0100 for memory check
	push	bp
	push	bx

ifdef	CLEAR_UMA				; Clear non-EMS UMBs if they
	call	clear_upper_memory		; exist to prevent parity errors
endif
	mov	bp, 2
	call	mem_test			; Memory check es:0 - es:0400
	mov	[ds:72h], si			; Restore reset flag
	pop	ax
	mov	cl, 6
	shr	ax, cl
	mov	[ds:13h], ax			; ax = memory size in KB
	pop	ax
	jnb	@@vector_ram_ok
	or	al, error_mem			; Show vector area bad

@@vector_ram_ok:
	mov	[ds:15h], al			; Save IPL error code
	xor	ax, ax
	push	ax
	push	ax
	push	ax
	push	ax
	push	ax
	mov	ax, 30h 			; Set up IBM-compatible stack
	mov	ss, ax				;   segment 0030h
	mov	sp, 100h			;   offset  0100h
	push	ds
	mov	bx, 0E000h			; Check BIOS eprom
	push	cs
	pop	ds				;   at F000:E000
	mov	ah, 1
	call	checksum			;   for valid checksum
	pop	ds				;   restore BDA<-ds
	jz	@@init_int
	or	[byte ds:15h], error_bios	; Checksum error BIOS eprom

@@init_int:
	cli					; Init interrupt controller
	mov	al, 13h
	out	20h, al
	mov	al, 8
	out	21h, al
	mov	al, 9
	out	21h, al
	mov	al, 0FFh
	out	21h, al
	push	ds
	xor	ax, ax				; 8 nonsense vectors begin table
	mov	es, ax				;   at segment 0000h
	push	cs
	pop	ds
	mov	cx, 8				; Vectors 00h - 07h unused
	xor	di, di				;   we start at vec 00h

@@low_vectors:
	mov	ax, offset ignore_int		; Nonsense interrupt from RSX
	stosw
	mov	ax, cs				;   BIOS ROM segment
	stosw
	loop	@@low_vectors

	mov	si, offset vectors		; si --> Vector address table
	mov	cx, 18h 			;   vectors 08h - 1Fh busy

@@high_vectors:
	movsw					; Set interrupt vector offset
	mov	ax, cs
	stosw					; Set interrupt vector segment (BIOS segment)
	loop	@@high_vectors

	mov	ax, 0F600h			; ax --> ROM BASIC segment
	mov	ds, ax				; ds -->  "	"     "
	xor	bx, bx				; bx  =  ROM BASIC offset
	mov	ah, 4				; Four BASIC ROMs to check

	mov	bp, sp				; Save the stack pointer
	push	cs				;   push code segment
	mov	dx, offset @@skip 		; Save the code offset
	push	dx				;   for RAM_PATCH subroutine
	mov	dx, 0EA90h			; mov dx, 'nop, JMP_FAR'
	push	dx				;   save it on stack
	mov	dx, 0178Bh			; mov dx, 'mov dx, [bx]'
	push	dx				;   save it on stack
	push	ss				; Save stack segment
	mov	dx, sp				;   get the stack offset
	add	dx, 02h 			;   calculate xfer address
	push	dx				;   save it on the stack

	retf					; Test for BASIC rom
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;	mov	dx, [bx] 			; Executes off the stack ;
;	jmpf	0F000h, skip			;   in RAM space         ;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
@@skip:	mov	sp, bp				; Restore the stack pointer
	cmp	dl, dh				;   compare 1st and 2nd byte
	je	@@kosher			;   perfection. No piracy

@@basic_rom:
	call	checksum			; Scan for BASIC roms
	jnz	@@kosher			;   bad BASIC rom
	dec	ah				; Continue
	jnz	@@basic_rom			;   yes, more

	pop	ds				; Else valid BASIC
	mov	di, 60h 			;   install BASIC

	xor	ax,ax				;   0000h BASIC interrupt offset
	stosw
	mov	ax, 0F600h			;   F600h BASIC interrupt segment
	stosw

	push	ds
@@kosher:
	pop	ds				; Setup special low vectors
	mov	[word es:8], offset int_2	;   NMI interrupt
	mov	[word es:14h], offset int_5	;   print screen interrupt
	mov	[word es:7Ch], 0		; No special graphics characters
	mov	[word es:7Eh], 0		;   so zero vector 1Fh
	mov	dx, 61h
	in	al, dx				; Read machine flags
	or	al, 00110000b			;   clear old parity error
	out	dx, al				; Write them back to reset
	and	al, 11001111b			;   enable parity
	out	dx, al				; Write back, parity enabled
	mov	al, 80h 			;   allow NMI interrupts
	out	0A0h, al
	mov	ax, 0000000000110000b		; Assume monochrome video
	mov	[ds:10h], ax			;   card has been installed
	int	10h				;   initialize if present
	mov	ax,0000000000100000b		; Assume color/graphics video
	mov	[ds:10h], ax			;   card has been installed
	int	10h				;   initialize if present

ifdef	IBM_PC					; Read 5150 switch config
	mov	al, 0CCh
	out	dx, al				; Reset keyboard
	in	al, 60h				; Read config switches
	mov	ah, al
else						; Read 5160 switch config
	in	al, 62h 			; Get memory size (64K bytes)
	and	al, 00001111b			;   in bits 2,3 low nibble
	mov	ah, al				; Save memory size nibble
	mov	al, 10101101b
	out	dx, al
	in	al, 62h 			; Get number of floppies (0-3)
endif
	mov	cl, 4				;   and init video mode
	shl	al, cl				;   shift in hi nibble
	or	al, ah
	mov	ah, 0

	mov	[ds:10h], ax			; Start building Equipment Flag
	and	al, 00110000b			;   if video card, mode set
	jnz	@@video_found			;   found video interface
	mov	ax, offset dummy_int		; No hardware, dummy_int becomes
	mov	[es:40h], ax			;   int_10 video service
	jmp	short @@skip_video

@@video_found:
	call	video_init			; Setup video

@@skip_video:
	mov	al, 00001000b			; Read low switches
	out	dx, al

	mov	cx, 2956h
@@keyb_delay:
	loop	@@keyb_delay

	mov	al, 11001000b			; Keyboard acknowledge
	out	dx, al 				;   send the request
	xor	al, 10000000b			; Toggle to enable
	out	dx, al 				;   send key enable
	mov	ax, 1Eh 			; Offset to buffer start
	mov	[ds:1Ah], ax			; Buffer head pointer
	mov	[ds:1Ch], ax			; Buffer tail pointer
	mov	[ds:80h], ax			; Buffer start
	add	ax, 20h 			;   size
	mov	[ds:82h], ax			; Buffer end
	mov	ax, 1414h			; Time-out value seconds
	mov	[ds:78h], ax			;   LPT1
	mov	[ds:7Ah], ax			;   LPT2
	mov	ax, 101h			; Time-out value seconds
	mov	[ds:7Ch], ax			;   COM1
	mov	[ds:7Eh], ax			;   COM2
	mov	si, offset lpt_ports		; si --> LPT port table
	xor	di, di				;   offset into data seg
	mov	cx, 3				;   number of printers

@@next_lpt:
	mov	dx, [cs:si]			; Get LPT port
	mov	al, 10101010b			;   write value
	out	dx, al				;   to the LPT
	mov	al, 11111111b			; Dummy data value
	out	0C0h, al			;   on the bus
	in	al, dx				; Read code back
	cmp	al, 10101010b			;   check code
	jnz	@@no_lpt			;   no printer found
	mov	[di+8], dx			; Save printer port
	inc	di
	inc	di

@@no_lpt:
	inc	si
	inc	si
	loop	@@next_lpt

	mov	ax, di				; Number of printers * 2
	mov	cl, 3				;   get shift count
	ror	al, cl				;   divide by eight
	mov	[ds:11h], al			;   save in equipment flag

	xor	di, di				; COM port(s) at 40:00 (hex)

@@com_1:
	mov	dx, 3FBh			; COM #1 line control reg.
	mov	al, 00011010b			;   7 bits, even parity
	out	dx, al				; Reset COM #1 line cont. reg
	mov	al, 11111111b			;   noise pattern
	out	0C0h, al			; Write pattern on data buss
	in	al, dx				;   read result from COM #1
	cmp	al, 00011010b			; Check if serial port exists
	jnz	@@com_2				;   skip if no COM #1 port
	mov	[word di], 3F8h 		; Else save port # in BDA
	inc	di				;   potential COM #2 port
	inc	di				;   is at 40:02 (hex)

@@com_2:
	mov	dx, 2FBh			; COM #2 line control reg
	mov	al, 00011010b			;   7 bits, even parity
	out	dx, al				; Reset COM #2 line cont. reg
	mov	al, 11111111b			;   noise pattern
	out	0C0h, al			; Write pattern on data bus
	in	al, dx				;   read results from COM #2
	cmp	al, 00011010b			; Check if serial port exists
	jnz	@@com_done			;   skip if no COM #2 port
	mov	[word di], 2F8h 		; Else save port # in BDA
	inc	di				;   total number of serial
	inc	di				;   interfaces times two

@@com_done:
	mov	ax, di				; Get serial interface count
	or	[ds:11h], al			;   equipment flag

	mov	cx, 100				; Check for game port 100 times
	mov	dx, 201h
@@check_game:
	in	al, dx				; Anything there?
	cmp	al, 0FFh
	jne	@@found_game			; Yep, game port is present
	dec	cx				; Otherwise keep polling
	jcxz	@@game_done			; Countdown is zero; no game port
	jmp	@@check_game
@@found_game:
	or	[byte ds:11h], 00010000b	; Set flag in equipment word
@@game_done:

	call	fpu_check			; Check for FPU

	mov	dx, 0C000h			; ROM segment start

	mov	bx, [ds:72h]			; Save warm boot flag
	push	bx				;   (Some ROM inits may trash it)
	push	ds

ifdef	TURBO_ENABLED
ifdef	TURBO_BOOT				; If defined enable turbo speed at bootup
	in	al, 61h 			; Read equipment flags
	xor	al, 00001100b			;   toggle speed
	out	61h, al 			; Write new flags back
endif
endif

@@find_rom:
	mov	ds, dx				; Load ROM segment
	jmp	short @@continue		; Jump over old int 2 location

;-----------------------------------------------
; IBM PC 5150 offset for int 2 (NMI)
;-----------------------------------------------
	entry	0E2C3h
	jmp	int_2				; Jump to new int 2 at IBM XT 5160 offset

@@continue:
	xor	bx, bx				;   ID offset
	mov	ax, [bx]			; Read the ROM ID
	cmp	ax, 0AA55h
	jnz	@@next_rom			;   not valid ROM
	mov	ax, 40h
	mov	es, ax
	mov	ah, 0
	mov	al, [bx+2]			; Get ROM size (bytes * 512)
	mov	cl, 5
	shl	ax, cl				; Now ROM size in segments
	add	dx, ax				;   add base segment
	mov	cl, 4
	shl	ax, cl				; ROM address in bytes
	mov	cx, ax				;   checksum requires cx
	call	checksum_entry			; Find ROM checksum
	jnz	@@bad_rom			;   bad ROM
	push	dx
	mov	[word es:67h], 3		; Offset for ROM being setup
	mov	[es:69h], ds			; Segment for ROM being setup
	call	[dword es:67h]			;   call ROM initialization
	pop	dx
	jmp	short @@continue_rom

@@bad_rom:
	or	[byte es:15h], error_rom	; ROM present, bad checksum

@@next_rom:
	add	dx, 80h 			; Segment for next ROM

@@continue_rom:
	cmp	dx, 0F600h			; End of ROM space?
	jl	@@find_rom			;  no, continue

	pop	ds
	pop	bx
	mov	[ds:72h], bx			; Restore warm boot flag

	in	al, 21h 			; Read 8259 interrupt mask
	and	al, 10111100b			;   enable IRQ (0, 1, 6) ints
	out	21h, al 			; (tod_clock, key, floppy_disk)

	mov	ah, 12h				; Test for EGA/VGA
	mov	bx, 0FF10h
	int	10h				; Video Get EGA Info
	cmp	bh, 0FFh			; If EGA or later present BH != FFh
	je	@@not_ega

	and	[byte ds:10h], 11001111b	; Set video flag in equipment list to EGA/VGA
	jmp	short @@skip_video_test

@@not_ega:
ifdef	TEST_VIDEO
	mov	al, [ds:49h]			; Get the video mode
	call	video_mem_test			; Do video memory test
	call	video_init			; Reinit video after test
endif

@@skip_video_test:
	mov	ah, 1
	mov	ch, 0F0h
	int	10h				; Set cursor type
	call	clear_screen			;   clear display

ifdef	ENHANCED_KEYB
	mov	[byte ds:96h], 00010000b	; Set flag to indicate enhanced keyboard
endif
	cmp	[word ds:72h], 1234h		; BIOS setup before?

	push	ds
	pop	es				; ES = DS (BDA, 0040h)
	push	cs
	pop	ds				; DS = CS (ROM, FE00h)

	jne	@@config			; No, it's a cold boot

@@skip_config:
	mov	bh, -3				; Position cursor at row 0 for boot BASIC message
	jmp	do_boot				; Else it's a warm boot

@@config:
	mov	si, offset str_banner
	call	color_print
	mov	si, offset str_banner_2
	call	print

	test	[byte es:15h], 11111111b	; Any errors so far?
	jz	@@no_errors			;   no, skip

	mov	ax, 0300h
print_error:
	call	locate
	mov	si, offset str_error
	call	print				; Print string
	mov	al, [es:15h]			;   get error number
	call	number				;   print hex value
	mov	si, offset str_continue
	call	print				;   print prompt
	mov	bl, 2				;   long beep
	call	beep
	call	get_key				; Wait for keypress
	push	ax				;   save answer
	call	out_char			;   echo answer
	pop	ax				;   get  answer
	cmp	al, 'Y' 			; Was it "Y"?
	jz	@@ignore_error			;   ok, continue
	cmp	al, 'y' 			; Was it "y"?
	jz	@@ignore_error			;   ok, continue
	jmpf	0F000h, cold_boot		; Else cold reset
@@ignore_error:
	mov	[byte es:15h], 0		; User wants to ignore error
	call	clear_screen
	jmp	@@config

@@no_errors:
	mov	ax, 0300h			; Where to move cursor
	call	locate				; Position cursor
	call	display_cpu			; Display CPU type

	mov	si, offset str_mono		; Assume mono video
	mov	ax, 0407h
	call	locate
	mov	al, [es:49h]			; Get CRT mode
	cmp	al, 7				; Is it mono?
	jz	@@display_video			; Yes
	mov	al, [es:10h]			; Check equipment word
	and	al, 00110000b			; Is it EGA/VGA?
	jnz	@@is_cga			; No, we have CGA
	mov	si, offset str_ega_vga		; Otherwise we have EGA/VGA
	jmp	short @@display_video
@@is_cga:
	mov	si, offset str_cga
@@display_video:
	call	print				; Print video adapter present

	mov	bx, 0507h
	mov	al, [es:11h]			; Get equipment byte
	push	ax
	mov	cl, 6
	ror	al, cl
	and	al, 3				; Number of LPT ports
	jz	@@display_com_ports		; Skip if none
	mov	bp, 8
	mov	si, offset str_parallel
	call	formatted_ascii_output		; Formatted ASCII output

@@display_com_ports:
	pop	ax
	push	ax
	mov	si, offset str_serial
	ror	al, 1				; Check for COM ports
	and	al, 3
	jz	@@display_game_port		; Skip if none
	xor	bp, bp
	call	formatted_ascii_output		; Formatted ASCII output

@@display_game_port:
	pop	ax				; Equipment byte restore
	mov	si, offset str_game
	test	al, 00010000b			; Check for game port
	jz	@@display_timer			; Skip if none
	mov	ax, bx
	call	locate				; Position cursor
	call	print				;   and print string
	inc	bh				;   scroll line

@@display_timer:
	call	timer_check			; Check for timer device
	jb	@@finish_device_list		; Skip if none
	mov	ax, bx
	call	locate				; Position cursor
	inc	bh
	mov	si, offset str_timer
	call	print

@@finish_device_list:
	dec	bh
	mov	bl, 7
	mov	ax, bx
	call	locate				; Correct line drawing character
	mov	si, offset str_last_line	;   displayed for last device
	call	print				;   on BIOS config screen

	inc	bh
	inc	bh
	xor	bl, bl
	mov	ax, bx				; Where to position cursor
	call	locate				;   position cursor
	mov	si, offset str_ram_test		; Memory size string
	call	print				;   print string

	push	es
	mov	bp, [es:13h]			; Memory size (1 K blocks)
	dec	bp
	dec	bp
	mov	si, 2
	mov	dx, si
	mov	ax, 80h
	mov	es, ax

	add	bl, 0Dh
	push	bx
@@mem_count:
	pop	ax				; Cursory check of memory
	push	ax

	mov	cx, es

	cmp	bp, 1				; Always show final memory size
	je	@@last_time

	test	cx, 0000000111111111b		; Only print memory size every 8K
	jz	@@show_mem_size

	xor	ch, ch				; If ch is cleared memory size isn't printed
@@show_mem_size:
	dec	dx
@@last_time:
	call	locate				; Position cursor
	call	print_mem_kb			; Print size in K
	inc	dx

	call	mem_test			; Memory check es:0 - es:0400
	jb	@@bad_ram			;   bad RAM found  (How ???)

	dec	bp
	jnz	@@mem_count
	pop	bx
	pop	es

ifdef	WARM_BOOT_BASIC
do_boot:
endif
	call	boot_basic			; Boot BASIC if space pressed

ifndef	WARM_BOOT_BASIC
do_boot:
endif
	mov	bl, 1				; Do a warm boot
	call	beep				;   short beep
	call	clear_screen			;   clear display

	xor	ax, ax
	mov	ds, ax
	mov	[word ds:472h], 1234h		; Show cold start done

	mov	ah, 1
	mov	cx, 0B0Ch			; Set underline cursor mono
	cmp	[byte ds:449h], 7		; Get CRT mode
	jz	@@is_mono			;   monochrome
	mov	cx, 607h			; Set underline cursor color
@@is_mono:
	int	10h				; Set the correct cursor shape

	int	19h				; Boot the machine

@@bad_ram:
	dec	bp
	pop	bx
	pop	es
	or	[byte es:15h], error_ram	; Show "Bad RAM" error
	inc	bh
	inc	bh
	xor	bl, bl
	mov	ax, bx
	jmp	print_error

endp	post


;---------------------------------------------------------------------------------------------------
; Displays string (si) with port number (al) converted to ASCII hex
;---------------------------------------------------------------------------------------------------
proc	formatted_ascii_output	near

	mov	dl, al				; Formatted ASCII output
@@loop:
	mov	ax, bx				; Get position for
	call	locate				;   cursor routine
	push	si				; Get string address
	call	print				;   print string
	mov	ax, [es:bp+0]			; Get port # to print
	call	big_number			;   four digits
	mov	si, offset str_h
	call	print
	pop	si				; Restore string address
	inc	bp				;   Address of port
	inc	bp				;   is two bytes long
	inc	bh				;   down one line
	dec	dl				; Decrement device count
	jnz	@@loop				;   back for more
	ret

endp	formatted_ascii_output


;---------------------------------------------------------------------------------------------------
; Increase memory size and display size if ch=0. Called during memory test at bootup.
;---------------------------------------------------------------------------------------------------
proc	print_mem_kb	near

	clc					; Clear carry flag
	mov	al, dl				;   Size "checked"
	inc	al				;   Show more
	daa
	mov	dl, al
	jnb	@@skip_carry
	mov	al, dh				;  Do carry
	adc	al, 0
	daa
	mov	dh, al
@@skip_carry:
	cmp	ch, 0
	jz	@@done
	mov	al, dh
	call	digit				; Print hex digit
	mov	al, dl
	mov	cl, 4
	ROR	al, cl
	call	digit				; Print hex digit
	mov	al, dl
	call	digit				; Print hex digit
@@done:
	ret

endp	print_mem_kb


;---------------------------------------------------------------------------------------------------
; Check for presence of hardware timer (cf=0 if timer present)
;---------------------------------------------------------------------------------------------------
proc	timer_check	near

	mov	dx, 241h			; Check for timer #2 port
	cli
	in	al, dx				;   read BCD seconds/100
	sti
	cmp	al, 99h 			; Are BCD digits in range?
	jbe	@@done				;   yes, port exists

	mov	dx, 341h			; Check for timer #1 port
	cli
	in	al, dx				;   read BCD seconds/100
	sti
	cmp	al, 99h 			; Are BCD digits in range?
	jbe	@@done				;   yes, port exists

	stc					; No hardware,	ports 0FFh
	ret
@@done:
	clc					; Found timer(s) answering
	ret

endp	timer_check


;---------------------------------------------------------------------------------------------------
; Clear display screen
;---------------------------------------------------------------------------------------------------
proc	clear_screen	near

	mov	dx, 184Fh			; Lower right corner of scroll
	xor	cx, cx				; Upper left  corner of scroll
	mov	ax, 600h			; Blank entire window
	mov	bh, 7				; Set regular cursor
	int	10h				; Call video service scroll
	mov	ah, 2				; Set cursor position
	xor	dx, dx				;   upper left corner
	mov	bh, 0				;   page 0
	int	10h				;   call video service
	mov	ax, 0500h			; Set active display page zero
	int	10h
	ret

endp	clear_screen


;---------------------------------------------------------------------------------------------------
; Display CPU present in system (8088 or V20)
;---------------------------------------------------------------------------------------------------
proc	display_cpu	near

	mov	si, offset str_system
	call	print
	call	cpu_check
	call	print

	mov	si, offset str_no_fpu
	test	[byte es:10h], 00000010b
	jz	@@no_fpu
	mov	si, offset str_8087
@@no_fpu:
	call	print
	ret

endp	display_cpu


;--------------------------------------------------------------------------------------------------
; Display value in ax as 4-character ASCII hex number
;--------------------------------------------------------------------------------------------------
proc	double_number

	push	ax				; Unsigned word
	mov	al, ah
	call	number
	jmp	big_number_entry

endp	double_number



str_banner_2	db	CR, LF, 'Additions by Ya`akov Miles (1987) and Jon Petrosky (2008-2012)', 0

str_ram_test	db	'Testing RAM:    K OK', 0

str_mono	db	195, ' Mono/Hercules Graphics', 0

str_insert_disk		db	'Insert BOOT disk in A:', CR, LF
			db	'Press any key when ready', CR, LF, LF, 0


;---------------------------------------------------------------------------------------------------
; Initial Program Load. Tries to boot from floppy first, then hard drive (external BIOS required
; for hard drive). If both fail ROM BASIC is run if present.
;---------------------------------------------------------------------------------------------------
	entry	0E600h
proc	ipl	near

	sti					; Enable interrupts
	xor	ax, ax
	mov	ds, ax
	mov	[word ds:78h], offset int_1E	; Get disk parameter table
	mov	[ds:7Ah], cs			;   save segment

	mov	ax, 6				; Try up to 6 times (4 floppy, 2 hard)

@@retry:
	push	ax				; Save retry count

	xor	dx, dx				; Assume floppy drive
	cmp	al, 2				; Tries above 2?
	ja	@@try				; Yes, use floppy
	or	dl, 10000000b			; Otherwise set bit 7 to use hard drive
@@try:
	push	dx				; Save drive number

	mov	ah, 0
	int	13h				; Reset drive

	pop	dx				; Restore drive number
	jb	@@failed

	xor	ax, ax
	mov	es, ax				; Segment 0
	mov	ax, 0201h			; One sector read

	mov	bx, 7C00h			;   offset  7C00
	mov	cl, 1				;   sector 1
	mov	ch, 0				;   track  0
	int	13h
	jb	@@failed
	jmpf	0000h, 7C00h			; Call the boot block

@@failed:
	pop	ax				; Get retries
	dec	al				;   one less
	jnz	@@retry

	or	ah, ah				; Disk present?
	jnz	@@disk_error			;   yes

@@no_disk:
	push	cs
	pop	ds
	mov	si, offset str_insert_disk	; Load disk message
	call	print				;   and print string
	call	get_key				;   wait for keypress

	mov	ax, 0FF08h			; Reset retry count
	jmp	@@retry				;   and retry

@@disk_error:
	xor	ax, ax
	mov	ds, ax
	mov	ax, [ds:62h]
	cmp	ax, 0F600h			; Check for valid ROM basic segment
	jne	@@no_disk			; No ROM basic found, keep retrying disk
	int	18h				;   else call ROM basic

endp	ipl


;---------------------------------------------------------------------------------------------------
; Test CPU. If any error is detected the system is halted.
;---------------------------------------------------------------------------------------------------
ifdef	TEST_CPU
proc	cpu_test	near

	xor	ax, ax				; Begin FLAG test of CPU
	jb	@@halt
	jo	@@halt
	js	@@halt
	jnz	@@halt
	jpo	@@halt
	add	ax, 1
	jz	@@halt
	jpe	@@halt
	sub	ax, 8002h
	js	@@halt
	inc	ax
	jno	@@halt
	shl	ax, 1
	jnb	@@halt
	jnz	@@halt
	shl	ax, 1
	jb	@@halt

	mov	bx, 0101010101010101b		; Begin REGISTER test of CPU
@@cpu_test:
	mov	bp, bx
	mov	cx, bp
	mov	sp, cx
	mov	dx, sp
	mov	ss, dx
	mov	si, ss
	mov	es, si
	mov	di, es
	mov	ds, di
	mov	ax, ds
	cmp	ax, 0101010101010101b
	jnz	@@cpu_1
	not	ax
	mov	bx, ax
	jmp	@@cpu_test

@@cpu_1:
	xor	ax, 1010101010101010b
	jnz	@@halt
	jmp	cpu_ok

@@halt:
	hlt

endp	cpu_test
endif


;---------------------------------------------------------------------------------------------------
; Int 9h Enhanced Keyboard Support. Intercepts and processes escaped scan codes (E0 prefix) and
; "fake" shifts before the standard Int 9h handler.
;---------------------------------------------------------------------------------------------------
ifdef	ENHANCED_KEYB
proc	int_9_enhanced	near

	cmp	al, 0E0h			; Is scan code E0?
	jne	@@continue			; No

	or	bl, 00000010b			; Set flag to indicate last scan code was E0h
@@ignore:
	pop	cx
	push	offset int_9_end		; Skip the standard Int 9h
	jmp	short @@done

@@continue:
	cmp	al, 57h				; F11 pressed?
	je	@@F11_F12
	cmp	al, 58h				; F12 pressed?
	je	@@F11_F12

	test	bl, 00000010b			; Was last scan code E0h?
	jz	@@done				; No

	and	bl, 11111101b			; Clear flag to indicate last scan code wasn't E0h

	cmp	al, 0AAh			; Check for escaped key up code
	jne	@@not_ext_up
	mov	al, bh				; If it is, get last escaped key down code
	or	al, 10000000b			; Set high bit to convert to key up
	mov	ah, al				; Save copy
@@not_ext_up:
	mov	bh, al				; Save current escaped scan code

	mov	cl, al				; Ignore all fake shifts
	and	cl, 01111111b
	cmp	cl, 02Ah
	je	@@ignore
	cmp	cl, 036h
	je	@@ignore

	cmp	al, 35h				; Process / with standard Int 9h
	je	@@done
	cmp	al, 1Ch				; ENTER
	je	@@done
	cmp	al, 1Dh				; Right CTRL
	je	@@done
	cmp	al, 38h				; Right ALT
	je	@@done
	cmp	al, 46h				; CTRL+Pause (Break)
	je	@@done

	call	check_ctrl_alt_del		; Check for CTRL+ALT+DEL combination with gray DEL

	call	set_insert_flags		; Check for gray INS key down and set insert flags
	jc	@@done				; Process key up codes normally

	mov	al, 0E0h			; Set ASCII to E0h for extended keystroke

@@stuff:
	pop	cx
	push	offset int_9_stuff		; Skip processing and put keystroke in buffer

@@done:
	mov	[ds:96h], bx			; Write back key flags
	ret

@@F11_F12:
	add	ah, 2Eh				; Convert protocol scan code to software

	mov	al, [ds:17h]
	test	al, 00001000b			; ALT key pressed?
	jnz	@@alt				;   yes
	test	al, 00000100b			; CTRL key pressed?
	jnz	@@ctrl				;   yes
	test	al, 00000011b			; Either shift key pressed?
	jnz	@@shift				;   yes
	jmp	short @@stuff_F11_F12

@@alt:
	add	ah, 2				; Adjust scan code for ALT+F11/F12
@@ctrl:
	add	ah, 2				; Adjust scan code for CTRL+F11/F12
@@shift:
	add	ah, 2				; Adjust scan code for SHIFT+F11/F12

@@stuff_F11_F12:
	xor	al, al				; Set ASCII to 0
	jmp	short @@stuff			; Stuff keystroke

endp	int_9_enhanced
endif


;---------------------------------------------------------------------------------------------------
; Interrupt 19h - Warm Boot
;---------------------------------------------------------------------------------------------------
	entry	0E6F2h				; IBM entry point for int 19h
proc	int_19	far

	jmp	ipl				; Warm boot

endp	int_19


;---------------------------------------------------------------------------------------------------
; Detect CPU type (8088 or V20)
;---------------------------------------------------------------------------------------------------
proc	cpu_check	near			; Test for 8088 or V20 CPU

	xor	al, al				; Clean out al to set ZF
	mov	al, 40h				; mul on V20 does not affect the zero flag
	mul	al				;   but on an 8088 the zero flag is used
	jz	@@have_v20			; Was zero flag set?
	mov	si, offset str_8088		;   No, so we have an 8088 CPU
	ret
@@have_v20:
	mov	si, offset str_v20		;   Otherwise we have a V20 CPU
	ret

endp	cpu_check


;---------------------------------------------------------------------------------------------------
; Detect if a FPU/NPU (8087) is present
;---------------------------------------------------------------------------------------------------
proc	fpu_check	near			; Test for FPU

	fninit					; Try to init FPU
	mov	si, 0200h
	mov	[byte si+1], 0			; Clear memory byte
	fnstcw	[word si]			; Put control word in memory
	mov	ah, [si+1]
	cmp	ah, 03h				; If ah is 03h, FPU is present
	jne	@@no_8087
	or	[byte ds:10h], 00000010b	; Set FPU in equp list
	ret
@@no_8087:
	and	[byte ds:10h], 11111101b	; Set no FPU in equp list
	ret

endp	fpu_check


;---------------------------------------------------------------------------------------------------
; Interrupt 14h - Serial RS232 Communications
;---------------------------------------------------------------------------------------------------
	entry	0E729h				; IBM entry point for baud rate generator table

baud	dw	0417h				;  110 baud clock divisor
	dw	0300h				;  150 baud clock divisor
	dw	0180h				;  300 baud clock divisor
	dw	00C0h				;  600 baud clock divisor
	dw	0060h				; 1200 baud clock divisor
	dw	0030h				; 2400 baud clock divisor
	dw	0018h				; 4800 baud clock divisor
	dw	000Ch				; 9600 baud clock divisor

	entry	0E739h				; IBM entry point for int 14h
proc	int_14	far

	sti					; Serial RS232 COM services
	push	ds				;   through 8250 UART (ugh)
	push	dx				;   dx = COM device (0 - 3)
	push	si
	push	di
	push	cx
	push	bx
	mov	bx, 40h
	mov	ds, bx
	mov	di, dx				;
	mov	bx, dx				; RS232 serial COM index (0-3)
	shl	bx, 1				;   index by bytes
	mov	dx, [bx]			; Convert index to port number
	or	dx, dx				;   by indexing 40:0
	jz	@@end				;   no such COM device, exit
	or	ah, ah				; Init on ah=0
	jz	@@init
	dec	ah
	jz	@@send				; Send on ah=1
	dec	ah
	jz	@@receive			; Receive on ah=2
	dec	ah
	jz	@@status			; Status on ah=3

@@end:
	pop	bx				; End of COM service
	pop	cx
	pop	di
	pop	si
	pop	dx
	pop	ds
	iret

@@init:
	push	ax				; Init COM port, al has data
						; = (Word Length in Bits - 5)
						;  +(1 if two stop bits) *  4
						;  +(1 if parity enable) *  8
						;  +(1 if parity even  ) * 16
						;  +(BAUD: select 0-7  ) * 32
	mov	bl, al
	add	dx, 3				; Line Control Register (LCR)
	mov	al, 80h 			;   index RS232_BASE + 3
	out	dx, al				; Tell LCR to set (latch) baud
	mov	cl, 4
	rol	bl, cl				; Baud rate selects by words
	and	bx, 00001110b			;   mask off extraneous
	mov	ax, [word cs:bx+baud]		; Clock divisor in ax
	sub	dx, 3				; Load in lo order baud rate
	out	dx, al				;   index RS232_BASE + 0
	inc	dx				; Load in hi order baud rate
	mov	al, ah
	out	dx, al				;   index RS232_BASE + 1
	pop	ax
	inc	dx				; Find Line Control Register
	inc	dx				;   index RS232_BASE + 3
	and	al, 00011111b			; Mask out the baud rate
	out	dx, al				;   set (censored) init stat
	mov	al, 0
	dec	dx				; Interrupt Enable Reg. (IER)
	dec	dx				;   index RS232_BASE + 1
	out	dx, al				; Interrupt is disabled
	dec	dx
	jmp	short @@status			; Return current status

@@send:
	push	ax				; Send al through COM port
	mov	al, 3
	mov	bh, 00110000b			; (Data Set Ready, Clear To Send)
	mov	bl, 00100000b			;   (Data Terminal Ready) wait
	call	@@wait				; Wait for transmitter to idle
	jnz	@@timeout			;   time-out error
	sub	dx, 5				;   (xmit) index RS232_BASE
	pop	cx				; Restore char to cl register
	mov	al, cl				;   get copy to load in UART
	out	dx, al				;   transmit char to 8250
	jmp	@@end				;   ah register has status

@@timeout:
	pop	cx				; Transmit error, restore char
	mov	al, cl				;   in al for compatibility
						;   fall through to generate error
@@timeout_2:
	or	ah, 80h 			; Set error (=sign) bit in ah
	jmp	@@end				;   common exit

@@receive:
	mov	al, 1				; Get char. from COM port
	mov	bh, 00100000b			; Wait on DSR (Data Set Ready)
	mov	bl, 00000001b			; Wait on DTR (Data Terminal Ready)
	call	@@wait				;   wait for character
	jnz	@@timeout_2			;   time-out error
	and	ah, 00011110b			; Mask ah for error bits
	sub	dx, 5				;   (receiver) index RS232_BASE
	in	al, dx				; Read the character
	jmp	@@end				;   ah register has status

@@status:
	add	dx, 5				; Calculate line control stat
	in	al, dx				;   index RS232_BASE + 5
	mov	ah, al				;   save high order status
	inc	dx				; Calculate modem stat. reg.
	in	al, dx				;   index RS232_BASE + 6
	jmp	@@end				;   save low  order status
						; ax = (DEL Clear_To_Send ) *     1
						;      (DEL Data_Set_ready) *     2
						;      (Trailing_Ring_Det.) *     4
						;      (DEL Carrier_Detect) *     8
						;      (Clear_To_Send     ) *    16
						;      (Data_Set_Ready    ) *    32
						;      (Ring_Indicator    ) *    64
						;      (Carrier_Detect    ) *   128
						;      ----------------------------
						;      (Char  received    ) *   256
						;      (Char smothered    ) *   512
						;      (Parity error      ) *  1024
						;      (Framing error     ) *  2048
						;      (Break detected    ) *  4096
						;      (Able to xmit      ) *  8192
						;      (Transmit idle     ) * 16384
						;      (Time out error    ) * 32768
@@poll:
	mov	bl, [byte di+7Ch]		; Wait on bh in status or error

@@loop:
	sub	cx, cx				; Outer delay loop
@@loop_2:
	in	al, dx				;   inner loop
	mov	ah, al
	and	al, bh				; And status with user bh mask
	cmp	al, bh
	jz	@@loop_exit			;   jump if mask set
	loop	@@loop_2			; Else try again
	dec	bl
	jnz	@@loop
	or	bh, bh				; Clear mask to show timeout
@@loop_exit:
	retn					; Exit ah reg. Z flag status

@@wait: add	dx, 4				; Reset the Modem Control Reg.
	out	dx, al				;   index RS232_BASE + 4
	inc	dx				; Calculate Modem Status Reg.
	inc	dx				;   index RS232_BASE + 6
	push	bx				; Save masks (bh=MSR, bl=LSR)
	call	@@poll				;   wait on MSR modem status
	pop	bx				;   restore wait masks bh, bl
	jnz	@@done				;   "Error Somewhere" by dec

	dec	dx				; Calculate Line Status Reg.
	mov	bh, bl				;   index RS232_BASE + 5
	call	@@poll				;   wait on LSR line status
@@done:
	retn					; Status in ah reg and Z flag

endp	int_14


str_error	db	'System Error: ', 0


;---------------------------------------------------------------------------------------------------
; Interrupt 16h - Keyboard BIOS Services
;---------------------------------------------------------------------------------------------------
proc	int_16	far

@@check:
	cli					; No interrupts, critical code
	mov	bx, [ds:1Ah]			;   point to buffer head
	cmp	bx, [ds:1Ch]			;   equal buffer tail?
	mov	ax, [bx]			;   (fetch, look ahead)
	sti					; Enable interrupts
	pop	bx
	pop	ds
	retf	2				; Do iret, preserve flags

@@shift:
	mov	ax, [ds:17h]			; Read keypad shift status
	jmp	short @@end

@@stuff:
	mov	ax, cx
	call	stuff_keyboard_buffer
	mov	al, 0				; al=0 if buffer ok (must be MOV; XOR modifies cf!)
	jnc	@@end
	inc	al				; al=1 if buffer full
	jmp	short @@end

	entry	0E82Eh				; IBM entry, key BIOS service
int_16_entry:

	sti					; Keyboard BIOS services
	push	ds
	push	bx

	mov	bx, 40h
	mov	ds, bx				; Load work segment

	cmp	ah, 5
	je	@@stuff				; Stuff keyboard buffer, ah=5

	mov	bx, ax				; Save function number to check for
						;   extended call later

	and	ah, 0Fh				; Translate enhanced keyboard function calls
						; ah=10h/11h/12h -> ah=00h/01h/02h
	or	ah, ah
	jz	@@read				; Read keyboard buffer, ah=0
	dec	ah
	jz	@@check				; Set Z if char ready, ah=1
	dec	ah
	jz	@@shift				; Return shift in al, ah=2

@@end:
	pop	bx				; Exit INT_16 keyboard service
	pop	ds
	iret

@@read:
	cli					; No interrupts, alters buffer
	mov	ax, [ds:1Ah]			;   point to buffer head
	cmp	ax, [ds:1Ch]			; If not equal to buffer tail
	jnz	@@have_char			;   char waiting to be read
	sti					; Else allow interrupts
	jmp	@@read				;   wait for him to type

@@have_char:
	test	bh, 10h				; Test for extended function call
	pushf					; Save zf for later

	xchg	ax, bx
	mov	ax, [bx]			; Fetch the character

	popf					; Is this an extended function call?
	jnz	@@no_translation		; Yes so don't change extended scan codes

	cmp	al, 0E0h			; Is scan code E0h?
	jne	@@no_translation
	xor	al, al				; If so translate to 00h for standard function
@@no_translation:

	inc	bx				; Point to next character
	inc	bx				;   char = scan code + shift
	mov	[ds:1Ah], bx			; Save position in head
	cmp	bx, [ds:82h]			;   buffer overflowed?
	jnz	@@end				;   no, done
	mov	bx, [ds:80h]			; Else reset to point at start
	mov	[ds:1Ah], bx			;   and correct head position
	jmp	short @@end

endp	int_16


;---------------------------------------------------------------------------------------------------
; Interrupt 9h - Keyboard Data Ready
;---------------------------------------------------------------------------------------------------
	entry	0E885h				; Align translation tables at correct place

ascii		db	000h, 037h, 02Eh, 020h	; Scan -> ASCII, sign bit set
		db	02Fh, 030h, 031h, 021h	;   if further work needed
		db	032h, 033h, 034h, 035h
		db	022h, 036h, 038h, 03Eh
		db	011h, 017h, 005h, 012h
		db	014h, 019h, 015h, 009h
		db	00Fh, 010h, 039h, 03Ah
		db	03Bh, 084h, 001h, 013h
		db	004h, 006h, 007h, 008h
		db	00Ah, 00Bh, 00Ch, 03Fh
		db	040h, 041h, 082h, 03Ch
		db	01Ah, 018h, 003h, 016h
		db	002h, 00Eh, 00Dh, 042h
		db	043h, 044h, 081h, 03Dh
		db	088h, 02Dh, 0C0h, 023h
		db	024h, 025h, 026h, 027h
		db	028h, 029h, 02Ah, 02Bh
		db	02Ch, 0A0h, 090h

non_alpha	db	032h, 036h, 02Dh, 0BBh	; Non-Alphabetic secondary
		db	0BCh, 0BDh, 0BEh, 0BFh	;   translation table
		db	0C0h, 0C1h, 0C2h, 0C3h
		db	0C4h, 020h, 031h, 033h
		db	034h, 035h, 037h, 038h
		db	039h, 030h, 03Dh, 01Bh
		db	008h, 05Bh, 05Dh, 00Dh
		db	05Ch, 02Ah, 009h, 03Bh
		db	027h, 060h, 02Ch, 02Eh
		db	02Fh

ctrl_upper	db	040h, 05Eh, 05Fh, 0D4h	; CTRL uppercase secondary
		db	0D5h, 0D6h, 0D7h, 0D8h	;   translation table
		db	0D9h, 0DAh, 0DBh, 0DCh	;   for non-ASCII control
		db	0DDh, 020h, 021h, 023h
		db	024h, 025h, 026h, 02Ah
		db	028h, 029h, 02Bh, 01Bh
		db	008h, 07Bh, 07Dh, 00Dh
		db	07Ch, 005h, 08Fh, 03Ah
		db	022h, 07Eh, 03Ch, 03Eh
		db	03Fh

ctrl_lower	db	003h, 01Eh, 01Fh, 0DEh	; CTRL lowercase secondary
		db	0DFh, 0E0h, 0E1h, 0E2h	;   translation table
		db	0E3h, 0E4h, 0E5h, 0E6h	;   for non-ASCII control
		db	0E7h, 020h, 005h, 005h
		db	005h, 005h, 005h, 005h
		db	005h, 005h, 005h, 01Bh
		db	07Fh, 01Bh, 01Dh, 00Ah
		db	01Ch, 0F2h, 005h, 005h
		db	005h, 005h, 005h, 005h
		db	005h

alt_key		db	0F9h, 0FDh, 002h, 0E8h	; ALT key secondary
		db	0E9h, 0EAh, 0EBh, 0ECh	;   translation table
		db	0EDh, 0EEh, 0EFh, 0F0h
		db	0F1h, 020h, 0F8h, 0FAh
		db	0FBh, 0FCh, 0FEh, 0FFh
		db	000h, 001h, 003h, 005h
		db	005h, 005h, 005h, 005h
		db	005h, 005h, 005h, 005h
		db	005h, 005h, 005h, 005h
		db	005h

num_pad		db	'789-456+1230.' 	; Keypad secondary translation

num_ctrl	db	0F7h, 005h, 004h, 005h	; Numeric keypad CTRL secondary
		db	0F3h, 005h, 0F4h, 005h	;   translation table
		db	0F5h, 005h, 0F6h, 005h
		db	005h

num_upper	db	0C7h, 0C8h, 0C9h, 02Dh	; Numeric keypad SHIFT secondary
		db	0CBh, 005h, 0CDh, 02Bh	;   translation table
		db	0CFh, 0D0h, 0D1h, 0D2h
		db	0D3h

	entry	0E987h				; IBM entry point for int 9h
proc	int_9	far

	sti					; Key press hardware interrupt
	push	ax
	push	bx
	push	cx
	push	dx
	push	si
	push	di
	push	ds
	cld
	mov	ax, 40h
	mov	ds, ax
	in	al, 60h 			; Read the scan code data
	push	ax				;   save it
	in	al, 61h 			; Get control port status
	push	ax				;   save it
	or	al, 10000000b			; Set "latch" bit to
	out	61h, al 			;   acknowledge data
	pop	ax				; Restore control status
	out	61h, al 			;   to enable keyboard
	pop	ax				;   restore scan code

	mov	ah, al				; Save copy of scan code

ifdef	ENHANCED_KEYB
	mov	bx, [ds:96h]			; Get enhanced keyboard status flag
	call	int_9_enhanced			; Process escaped scan codes first
endif

	cmp	al, 11111111b			;   check for overrun
	jnz	@@process			;   no, OK

	jmp	@@beep				; Else beep bell on overrun

int_9_end:
@@end:
	mov	al, 20h 			; Send end_of_interrupt code
	out	20h, al 			;   to 8259 interrupt chip

@@exit:
	pop	ds				; Exit the interrupt
	pop	di
	pop	si
	pop	dx
	pop	cx
	pop	bx
	pop	ax
	iret

@@process:
	and	al, 01111111b			; Valid scan code, no break
	cmp	al, 46h
	jbe	@@standard			; Standard key
	jmp	@@pad				; Numeric keypad key

@@standard:
	mov	bx, offset ascii		; Table for ESC thru Scroll Lck
	xlat	[cs:bx] 			;   translate to Ascii
	or	al, al				; Sign flags "Shift" type key
	js	@@flag				;   shift, caps, num, scroll etc
	or	ah, ah				; Invalid scan code?
	js	@@end				;   exit if so
	jmp	short @@ascii			; Else normal character

@@flag: and	al, 01111111b			; Remove sign flag bit
	or	ah, ah				;   check scan code
	js	@@shift_up			;   negative, key released
	cmp	al, 10h 			; Is it a "toggle" type key?
	jnb	@@toggle			;   yes
	or	[ds:17h], al			; Else set bit in "flag" byte
	jmp	@@end				;   and exit

@@toggle:
	test	[byte ds:17h], 00000100b	; Control key pressed?
	jnz	@@ascii				;   yes, skip
	test	al, [ds:18h]			; Else check "CAPS, NUM, SCRL"
	jnz	@@end				;   set, invalid, exit
	or	[ds:18h], al			; Show set in "flag_1" byte
	xor	[ds:17h], al			;   flip bits in "flag" byte
	jmp	@@end

@@shift_up:
	cmp	al, 10h 			; Released - is it "toggle" key
	jnb	@@toggle_up			;   skip if so
	not	al				; Else form two's complement
	and	[ds:17h], al			;   to do BIT_CLEAR "flags"
	cmp	al, 11110111b			; ALT key release special case
	jnz	@@end				;   no, exit
	mov	al, [ds:19h]			; Else get ALT-keypad character
	mov	ah, 0				;   pretend null scan code
	mov	[ds:19h], ah			;   zero ALT-keypad character
	cmp	al, ah				; Was there a valid ALT-keypad?
	jz	@@end				;   no, ignore, exit
	jmp	@@null				; Else stuff it in ASCII buffer

@@toggle_up:
	not	al				; Form complement of toggle key
	and	[ds:18h], al			;   to do BIT_CLEAR "flag_1"
	jmp	@@end

@@ascii:
	test	[byte ds:18h], 00001000b	; Scroll lock pressed?
	jz	@@no_lock			;   no
	cmp	ah, 45h 			; Is this a NUM LOCK character?
	jz	@@done				;   no
	and	[byte ds:18h], 11110111b	; Else clear bits in "flag_1"

@@done:	jmp	@@end				;   and exit

@@no_lock:
	mov	dl, [ds:17h]
	test	dl, 00001000b			; ALT key pressed?
	jnz	@@alt				;   yes
	test	dl, 00000100b			; CTRL key pressed?
	jnz	@@ctrl				;   yes
	test	dl, 00000011b			; Either shift key pressed?
	jnz	@@shift				;   yes

@@lower_case:
	cmp	al, 1Ah 			; Alphabetic character?
	ja	@@non_alpha			;   no
	add	al, 'a'-1			; Else add lower case base
	jmp	@@common

@@non_alpha:
	mov	bx, offset non_alpha		; Non-alphabetic character
	sub	al, 20h
	xlat	[cs:bx] 			;   do the xlate
	jmp	@@common

@@alt:	cmp	al, 1Ah 			; Control key pressed?
	ja	@@no_ctrl			;   no, skip
	mov	al, 0				; Else illegal key press
	jmp	@@buffer

@@no_ctrl:
	mov	bx, offset alt_key		; Load ALT key translation
	sub	al, 20h 			;   bias to printing char
	xlat	[cs:bx] 			;   do the translation
	jmp	@@common

@@ctrl: cmp	ah, 46h 			; Scroll lock key?
	jnz	@@ctrl_1			;   no, skip
	mov	[byte ds:71h], 10000000b	; Else CTRL-"Scroll" = break
	mov	ax, [ds:80h]			;   get key buffer start
	mov	[ds:1Ch], ax			;   get key tail to start
	mov	[ds:1Ah], ax			;   get key head to start
	int	1Bh				; Issue a "Break" interrupt
	sub	ax, ax
	jmp	@@common_2

@@ctrl_1:
	cmp	ah, 45h 			; Num lock key?
	jnz	@@ctrl_2			;   no, skip
	or	[byte ds:18h], 00001000b	; Else show scroll lock
	mov	al, 20h 			;   send end_of_interrupt
	out	20h, al 			;   to 8259 int controller
	cmp	[byte ds:49h], 7		; Monochrome monitor?
	jz	@@poll				;   yes, skip
	mov	dx, 3D8h			; Else reset mode
	mov	al, [ds:65h]			;   for the
	out	dx, al				;   CGA color card

@@poll: test	[byte ds:18h], 00001000b	; Wait for him to type
	jnz	@@poll				;   not yet
	jmp	@@exit

@@ctrl_2:
	cmp	ah, 3				; Is it a Control @ (null) ?
	jnz	@@ctrl_3			;   no
	mov	al, 0				; Else force a null

@@ctrl_4:
	jmp	@@buffer			;   save in buffer

@@ctrl_3:
	cmp	al, 1Ah 			; Is it a control character?
	jbe	@@ctrl_4			;   yes
	mov	bx, offset ctrl_lower		; Else non-ascii control
	sub	al, 20h 			;   lower case
	xlat	[cs:bx] 			;   translation
	jmp	@@common

@@shift:
	cmp	ah, 37h 			; Print_Screen pressed?
	jnz	@@shift_2
	mov	al, 20h 			; Yes, send end_of_interrupt
	out	20h, al 			;   to 8259 interrupt chip
	int	5				; Request print_screen service
	jmp	@@exit				;   and exit key service

@@shift_2:
	cmp	al, 1Ah 			; Alphabetic char?
	ja	@@shift_3			;   no
	add	al, 'A'-1			; Yes, add base for alphabet
	jmp	@@common

@@shift_3:
	mov	bx, offset ctrl_upper		; Non-ascii control
	sub	al, 20h 			;   upper case
	xlat	[cs:bx] 			;   translation
	jmp	@@common

@@pad:
	sub	al, 47h 			; Keypad key, convert origin
	mov	bl, [ds:17h]			;   get "flag" byte
	test	bl, 00001000b			; Look for ALT keypad entry
	jnz	@@alt_num			;   do special entry thing
	test	bl, 00000100b			; CTRL key pressed?
	jnz	@@released			;   skip if so
	test	bl, 00100000b			; Toggle "Num Lock" ?
	jz	@@pad_1				;   no, continue
	test	bl, 00000011b			; Shift keys hit?
	jnz	@@pad_2				;   no, check "INS"
	jmp	short @@pad_5			; Else xlat keypad char.

@@pad_1:
	test	bl, 00000011b			; Shift keys hit?
	jz	@@pad_2				;   no, check "INS" key
	jmp	short @@pad_5			; Else xlat keypad char.

@@alt_num:
	or	ah, ah				; ALT-keypad entry, scan code
	js	@@done_2			;   out of range
	test	[byte ds:17h], 00000100b	; Else check CTRL state
	jz	@@alt_num_2			;   not pressed, ALT keypad

@@turbo_patch:
	cmp	ah, 53h 			; Patch for CTRL ALT - toggle
	jnz	@@turbo_check			;   not a DEL (reset)
reboot:
	mov	[word ds:72h], 1234h		; Ctrl-Alt-Del,	set init flag
	jmp	warm_boot			;   do a warm reboot

@@turbo_check:
ifdef	TURBO_ENABLED
	cmp	ah, 4Ah 			; Is it a keypad "-" ?
	jnz	@@alt_num_2			;   no, skip
	call	toggle_turbo
endif

@@alt_num_2:
	mov	bx, offset num_pad		; Get keypad translation table
	xlat	[cs:bx] 			;   convert to number
	cmp	al, '0' 			; Is it a valid ASCII digit?
	jb	@@done_2			;   no, ignore it
	sub	al, 30h 			; Else convert to number
	mov	bl, al				;   save a copy
	mov	al, [ds:19h]			; Get partial ALT-keypad sum
	mov	ah, 0Ah 			;   times 10 (decimal)
	mul	ah
	add	al, bl				; Add in new digit to sum
	mov	[ds:19h], al			;   save as new ALT entry

@@done_2:
	jmp	@@end				; End_of_interrupt, exit

@@released:
	or	ah, ah				; Key released?
	js	@@done_2			;   ignore if so
	mov	bx, offset num_ctrl		; Else Numeric Keypad Control
	xlat	[cs:bx] 			;   secondary translate
	jmp	short @@common			;   and save it

@@pad_2:
	call	set_insert_flags		; Check for INS press and set
	jc	@@done_2			;   flags accordingly

@@pad_4:
	mov	bx, offset num_upper		; Numeric Keypad Upper Case
	xlat	[cs:bx] 			;   secondary translation
	jmp	short @@common

@@pad_5:
	or	ah, ah				; Was the key released?
	js	@@done_2			;   yes, ignore
	mov	bx, offset num_pad		; Load translation table
	xlat	[cs:bx] 			;   do translate

@@common:
	cmp	al, 5				; Common entry, char in al
	jz	@@done_3			;   Control E, ignore
	cmp	al, 4
	ja	@@common_1			; Above Control D

	or	al, 10000000b			; Else set sign flag
	jmp	short @@common_2

@@common_1:
	test	al, 10000000b			; Is sign bit set?
	jz	@@common_3			;   skip if so
	and	al, 01111111b			; Else mask sign off

@@common_2:
	mov	ah, al				; Save in high order byte
	mov	al, 0				;   set scan code to zero

@@common_3:
	test	[byte ds:17h], 01000000b	; Test for "CAPS LOCK" state
	jz	@@buffer			;   no, skip
	test	[byte ds:17h], 00000011b	; Test for SHIFT key
	jz	@@common_4			;   skip if no shift
	cmp	al, 'A' 			; Check for alphabetic key
	jb	@@buffer			;   not SHIFT_able
	cmp	al, 'Z' 			; Check for alphabetic key
	ja	@@buffer			;   not SHIFT_able
	add	al, 20h 			; Else do the shift
	jmp	short @@buffer

@@common_4:
	cmp	al, 'a' 			; Check for alphabetic key
	jb	@@buffer			;   not SHIFT_able
	cmp	al, 'z' 			; Check for Alphabetic key
	ja	@@buffer			;   not SHIFT_able
	sub	al, 20h 			; Else do the shift

int_9_stuff:
@@buffer:
	call	stuff_keyboard_buffer		; Put keystroke in buffer
	jnc	@@done_3

@@beep:
	mov	bl, 1				; Do a
	call	beep				;   short beep

@@done_3:
	jmp	@@end

@@null: mov	ah, 38h 			; ALT key pressed, released
	jmp	@@buffer			;   for no logical reason

endp	int_9


;---------------------------------------------------------------------------------------------------
; Check for INS key up/down scan codes and set flags. cf=1 if scan code is any key up.
;---------------------------------------------------------------------------------------------------
proc	set_insert_flags	near

	cmp	ah, 0D2h			; Was "INS" key released?
	jnz	@@pad_3
	and	[byte ds:18h], 01111111b	; Yes, clear "INS" in "FLAG_1"

@@done_2:
	stc
	ret

@@pad_3:
	or	ah, ah				; Key released?
	js	@@done_2			;   ignore if so

	cmp	ah, 52h 			; Else check for "INS" press
	jnz	@@done				;   not "INS" press
	test	[byte ds:18h], 10000000b	; Was INS key in effect?
	jnz	@@done				;   yes, ignore
	xor	[byte ds:17h], 10000000b	; Else tog "INS" in "FLAG" byte
	or	[byte ds:18h], 10000000b	;   set "INS" in "FLAG_1" byte

@@done:
	clc
	ret

endp


;---------------------------------------------------------------------------------------------------
; Put keystroke in ax (al=ASCII, ah=scan) in the keyboard buffer. cf=1 if buffer is full.
;---------------------------------------------------------------------------------------------------
proc	stuff_keyboard_buffer	near

	mov	bx, [ds:1Ch]			; bx = tail of buffer
	mov	di, bx				;   save it
	inc	bx				;   advance
	inc	bx				;   by word
	cmp	bx, [ds:82h]			; End of buffer reached?
	jnz	@@check				;   no, skip
	mov	bx, [ds:80h]			; Else bx = beginning of buffer

@@check:
	cmp	bx, [ds:1Ah]			; bx = Buffer Head ?
	jnz	@@stuff				;   no, OK
	stc					; cf=1, buffer full
	ret

@@stuff:
	mov	[ds:di], ax			; Stuff scan code, char in buffer
	mov	[ds:1Ch], bx			;   and update buffer tail
	clc					; cf=0, no errors
	ret

endp


;---------------------------------------------------------------------------------------------------
; Toggles TURBO speed and sounds high/low blip on the PC speaker to indicate current speed
;---------------------------------------------------------------------------------------------------
ifdef	TURBO_ENABLED
proc	toggle_turbo	near

	push	ax
	push	bx
	push	cx
	in	al, 61h 			; Read equipment flags
	xor	al, 00001100b			;   toggle speed
	out	61h, al 			; Write new flags back

	mov	bx, 0F89h			; low pitch blip
	and	al, 4				; Is turbo mode set?
	jz	@@do_beep
	mov	bx, 52Eh			; high pitch blip

@@do_beep:
	mov	al, 10110110b			; Timer IC 8253 square waves
	out	43h, al 			;   channel 2, speaker
	mov	ax, bx
	out	42h, al 			;   send low order
	mov	al, ah				;   load high order
	out	42h, al 			;   send high order
	in	al, 61h 			; Read IC 8255 machine status
	push	ax
	or	al, 00000011b
	out	61h, al 			; Turn speaker on
	mov	cx, 2000h
@@delay:
	loop    @@delay
	pop	ax
	out	61h, al 			; Turn speaker off
	pop	cx
	pop	bx
	pop	ax
	ret

endp	toggle_turbo
endif


str_no_basic	db	'No ROM BASIC, booting from disk...', 0


;---------------------------------------------------------------------------------------------------
; Interrupt 13h - Floppy Disk Services
;---------------------------------------------------------------------------------------------------
	entry	0EC59h				; IBM entry point for floppy
proc	int_13	far

	sti					; Floppy disk services
	push	bp
	push	si
	push	di
	push	ds
	push	es
	push	bx
	mov	di, ax				; Request type in di, for index
	xor	ax, ax
	mov	ds, ax
	les	si, [dword ds:78h]		; Get disk parameter table
	mov	ax, 40h
	mov	ds, ax
	mov	bx, 5
	mov	ax, [es:bx+si]			; Get (Gap Length, DTL) in ax
	push	ax				;   save it
	dec	bx
	dec	bx
	mov	ax, [es:bx+si]			; Get (Bytes/sector, EOT) in ax
	push	ax				;   save it
	xchg	cl, dh
	xchg	dl, cl
	push	dx				; Push (Head, Drive) swapped
	push	cx
	push	di
	mov	bp, sp				; Mark bottom of stack frame

ifdef	SLOW_FLOPPY
	call	floppy_speed			;   execute request at low speed
else
	call	floppy_exec			;   execute at current speed
endif

	mov	ah, [es:si+2]			; Get new motor count
	mov	[ds:40h], ah			;   and save it
	mov	ah, [ds:41h]			; Get completion status
	cmp	ah, 1				;   check for write protect
	cmc					;   was write protect error
	pop	bx
	pop	cx
	pop	dx
	xchg	dl, cl
	xchg	cl, dh
	pop	bx				; Clean
	pop	bx				;   up
	pop	bx				;   stack
	pop	es
	pop	ds
	pop	di
	pop	si
	pop	bp
	retf	2

floppy_exec:
	mov	al, [bp+1]			; Get floppy service number
	or	al, al
	jz	@@reset				;   reset, ah=0
	dec	al
	jz	@@status			;   read status, ah=1
	cmp	[byte bp+2], 3			; For track number above 3?
	ja	@@error				;   yes
	cmp	al, 5				; Service within range?
	jbe	@@exec				;   yes

@@error:
	mov	[byte ds:41h], 1		; Say write protect error
	retn

@@exec:	jmp	@@service			; Execute legal service

@@status:
	mov	al, [ds:41h]			; Return NEC status byte
	retn

@@reset:
	mov	dx, 3F2h			; Reset the floppy disk system
	cli
	and	[byte ds:3Fh], 00001111b	; Clear "write in progress"
	mov	al, [ds:3Fh]			;   find out busy drives
	mov	cl, 4
	shl	al, cl
	test	al, 00100000b
	jnz	@@reset_1			; Drive #1 active
	test	al, 01000000b
	jnz	@@reset_2			; Drive #2 active
	test	al, 10000000b
	jz	@@reset_0			; Drive #3 idle

@@reset_3:
	inc	al
@@reset_2:
	inc	al
@@reset_1:
	inc	al
@@reset_0:
	mov	[byte ds:3Eh], 0		; All drives need recalibrate
	mov	[byte ds:41h], 0		;   no completion status
	or	al, 00001000b			; Interrupt ON in command word
	out	dx, al				;   send word to controller
	or	al, 00000100b			; "Reset" in command word
	out	dx, al				;   send word to controller
	sti
	call	@@nec_busy			; Wait for completion
	call	nec_status			;   read result block
	mov	al, [ds:42h]
	cmp	al, 0C0h			; Did the reset work
	jz	@@reset_ok			;   yes
	mov	[byte ds:41h], 20h		; Else set controller error
	jmp	short @@done			;   return

@@reset_ok:
	mov	al, 3				; Specify command to NEC
	call	nec_chip			;   send it
	mov	al, [es:si]			; First byte in param block
	call	nec_chip			;   send it
	mov	al, [es:si+1]			; Second byte in param block
	call	nec_chip			;   send it

@@done: retn

func_table	db	003h, 000h, 0E6h, 0C5h, 0E6h, 04Dh	; NEC function table lookup
dma_table	db	000h, 000h, 046h, 04Ah, 042h, 04Ah	; DMA modes for 8237
write_table	db	000h, 000h, 000h, 080h, 000h, 080h	; Write flag table lookup
drive_table	db	1, 2, 4, 8				; Drive number table lookup
error_table	db	80h, 20h, 10h, 4, 2, 1			; Error code table lookup
status_table	db	04h, 10h, 08h, 04h, 03h, 02h, 20h	; Disk status table lookup

@@service:
	cli					; Normal (non-reset) commands
	mov	[byte ds:41h], 0		;   reset status
	mov	al, [bp+1]			; Get command word
	mov	ah, 0
	mov	di, ax				; Save copy, zero-extended
	out	0Ch, al 			;   diddle LSB/MSB flip-flop
	mov	al, [cs:di+dma_table]		; Fetch DMA mode
	out	0Bh, al 			;   send it to init_dma_controller
	mov	ax, [bp+0Ch]			; Get segment address
	mov	cl, 4				;   convert
	rol	ax, cl				;   to (offset, 64K page number)
	mov	ch, al				; Extract page number (0-15)
	and	ch, 00001111b			;   for 8237 DMA controller
	and	al, 11110000b			; Extract implicit page offset
	add	ax, [bp+0Ah]			;   add explicit user offset
	adc	ch, 0				;   (page number overflowed)
	mov	dx, ax				; Now save low 16 bits of address
	out	4, al				;   send lowest 8 bits  " "
	mov	al, ah
	out	4, al				;   send next 8 bits  " "
	mov	al, ch
	out	81h, al 			; 64K page number to DMA page reg
	mov	ah, [bp+0]
	mov	al, 0
	shr	ax, 1				; Sector count * 128
	mov	cl, [bp+6]			; Track count
	shl	ax, cl				;  * sector count
	dec	ax				; - 1
	out	5, al				; Send 1/2 of the word count
	xchg	al, ah
	out	5, al				; Send 2/2 of the word count
	xchg	al, ah
	add	ax, dx				; Compute final address
	jnb	@@disable_dma			;   ok
	sti
	mov	[byte ds:41h], 9h		; Else wrapped around 64K byte
	jmp	@@overflow			;   page register

@@disable_dma:
	mov	al, 2				; Disable floppy disk dma
	out	0Ah, al
	mov	[byte ds:40h], 0FFh		; Set large motor timeout
	mov	bl, [bp+2]			;   get drive number
	mov	bh, 0
	mov	al, [cs:bx+drive_table]		; Table lookup bit position
	mov	ch, al				;   save mask
	mov	cl, 4
	shl	al, cl				; Shift mask into place
	or	al, bl				;   or in drive select
	or	al, 0Ch 			;   or in DMA and NO RESET
	mov	dx, 3F2h
	out	dx, al				; Send to floppy control port
	sti
	mov	al, [cs:di+write_table]		; Table lookup for write flag
	or	[ds:3Fh], al			;   set write flag if active
	or	al, al
	jns	@@check_calibration		;   skip if non-write
	mov	ah, [es:si+0Ah] 		; Motor start from param blk
	or	ah, ah
	jz	@@check_calibration		;   none specified
	test	ch, [ds:3Fh]			; Was this drive motor running?
	jnz	@@check_calibration		;   skip if so
	call	@@wait				; Else delay for motor start

@@check_calibration:
	or	[ds:3Fh], ch			; Show this motor is running
	test	ch, [ds:3Eh]			; Drive recalibration needed?
	jnz	@@seek				;   no, skip
	or	[ds:3Eh], ch			; Else show recalibrated
	mov	al, 7				; Send RECAL command
	call	nec_chip			;   to NEC 765 chip
	mov	al, bl
	call	nec_chip			;   drive number
	call	@@nec_busy			; Wait for completion of RECAL
	call	nec_return			;   dummy call to ret

@@seek: mov	al, 0Fh 			; Request a seek
	call	nec_chip			;   from the NEC 765
	mov	al, bl
	call	nec_chip			; Drive number
	mov	al, [bp+3]
	call	nec_chip			; Cylinder number
	call	@@nec_busy			;   wait for completion
	call	nec_status			;   read results
	mov	al, [es:si+9]			; Get head settle time
	or	al, al				;   none specified?
	jz	@@translate			;   if none, skip

@@head_settle:
	mov	cx, 226h			; Delay time for head settle
@@head_delay:
	loop	@@head_delay			;   timed wait
	dec	al				;   delay in millisec
	jnz	@@head_settle			;   wait some more

@@translate:
	mov	al, [cs:di+func_table]		; Translate user service, then
	call	nec_chip			;   and send as NEC func
	mov	al, [bp+4]			;
	and	al, 1
	shl	al, 1
	shl	al, 1
	or	al, bl
	call	nec_chip
	cmp	[byte bp+1], 5			; Is this a format request?
	jnz	@@not_format			;   skip if not
	mov	al, [bp+6]			; Else use user bytes/sector
	call	nec_chip
	mov	al, [bp+7]			;   user EOT
	call	nec_chip
	mov	al, [es:si+7]			; Disk table format gap length
	call	nec_chip
	mov	al, [es:si+8]			; Disk table format fill byte
	call	nec_chip
	jmp	short @@completion

@@not_format:
	mov	cx, 7				; Else lookup bytes * 512/sec
	mov	di, 3				;   from disk table

@@table_loop:
	mov	al, [bp+di]			; al has bytes/sector * 512
	call	nec_chip
	inc	di				;   get next item for table
	loop	@@table_loop			;   also (EOT, GAP, DTL...)

@@completion:
	call	@@nec_busy			; Wait on floppy I/O completion
	call	nec_status_alt			;   get NEC status
	mov	al, [ds:42h]			;   into al
	and	al, 11000000b			; Isolate errors
	jz	@@read_done			;   no errors
	cmp	al, 40h 			; Test direction bit
	jz	@@error_code
	mov	[byte ds:41h], 20h		; Set if bad controller
	jmp	short @@read_done		;   return error

@@error_code:
	mov	al, [ds:43h]			; Read return code from block
	mov	cx, 6				;   number of error types
	xor	bx, bx				; Start at error type 0

@@error_loop:
	test	al, [cs:bx+error_table]		; Has error type bx occured?
	jnz	@@xlat_error			;   yes
	inc	bx				; Else try next error type
	loop	@@error_loop			;   until done

@@xlat_error:
	mov	al, [cs:bx+status_table]	; Translate error code again
	mov	[ds:41h], al			;   store it as disk status

@@read_done:
	mov	al, [ds:45h]			; Get bytes read
	cmp	al, [bp+3]			;   compare with requested
	mov	al, [ds:47h]			; Read sectors requested
	jz	@@skip				;   return if all read
	mov	al, [bp+7]			; Else read sectors requested
	inc	al				;   add one for luck

@@skip: sub	al, [bp+5]			; Subtract stectors read
	retn

@@overflow:
	mov	al, 0				; Overflowed 64K page boundary
	retn					;   show no sectors read

@@nec_busy:
	sti					; Wait for operation to finish
	xor	cx, cx				;   zero low order delay
	mov	al, 2				; Load high order delay

@@busy_wait:
	test	[byte ds:3Eh], 10000000b	; Has interrupt set the flag?
	clc					;   hack to slow CPU
	jnz	@@complete			;   yes
	loop	@@busy_wait			; Else back for more
	dec	al
	jnz	@@busy_wait

	mov	[byte ds:41h], 80h		; Time-out, say it completed
	pop	ax
	mov	al, 0				;   return time out code
	stc					;   error status
	retn

@@complete:
	and	[byte ds:3Eh], 01111111b	; Mask off completion status
	retn					;   return carry clear

nec_ready:
	push	cx				; Wait for NEC ready for comand
	xor	cx, cx
	mov	dx, 3F4h			;   NEC status port

@@ready_wait:
	in	al, dx				; Read status of NEC 765 chip
	or	al, al
	js	@@ready_ok			;   able to accept command
	loop	@@ready_wait
	mov	[byte ds:41h], 80h		; Else show timeout error
	jmp	short @@ready_error

@@ready_ok:
	test	al, 01000000b			; Test the direction bit
	jnz	@@ready_load
	mov	[byte ds:41h], 20h		;   clear if controller error

@@ready_error:
	pop	cx
	stc
	retn

@@ready_load:
	inc	dx				; Load NEC data port
	in	al, dx				;   read it
	push	ax

	mov	cx, 0Ah 			; Short delay
@@ready_delay:
	loop	@@ready_delay

	dec	dx				; Load NEC status port
	in	al, dx				;   read status
	test	al, 00010000b			;   set Z flag if done
	clc					;   return success
	pop	ax
	pop	cx
	retn

@@wait: push	cx				; Millisecond delay in ah
@@delay:
	xor	cx, cx
@@loop:	loop	@@loop
	dec	ah
	jnz	@@delay
	pop	cx
	retn

endp	int_13


;---------------------------------------------------------------------------------------------------
; Test video memory (Mono/Herc/CGA only)
;---------------------------------------------------------------------------------------------------
ifdef	TEST_VIDEO
proc	video_mem_test	near

	mov	bp, 4				; Assume monochrome, 4K memory
	mov	bx, 0B000h			;   segment in bx
	cmp	al, 7				; Is video mode mono?
	jz	@@do_test			;   yes, skip

	mov	bp, 10h 			; Else CGA, has 16K memory
	mov	bx, 0B800h			;   segment in bx

@@do_test:
	push	bx				; Load video seg in es
	pop	es
	mov	al, [ds:65h]			; Get CRT hardware mode
	and	al, 11110111b			;   disable video
	mov	dx, [ds:63h]			; Get 6845 index port
	add	dx, 4				;   add offset for
	out	dx, al				; 6845 controller port

@@loop:
	call	mem_test			; Memory check es:0 - es:0400
	dec	bp
	jnz	@@loop				; Loop until Video RAM checked
	jnb	@@test_ok
	or	[byte ds:15h], error_video	; Set Video RAM error in status

@@test_ok:
	ret

endp	video_mem_test
endif


;---------------------------------------------------------------------------------------------------
; Clear upper memory region if defined
;---------------------------------------------------------------------------------------------------
ifdef	CLEAR_UMA
proc	clear_upper_memory	near

	push	es
	xor	ax, ax				; Zero out memory
ifdef	UMA_START
	mov	bx, UMA_START			; Starting segment
else
	mov	bx, 0A000h
endif

@@loop:
	xor	di, di				; Target offset always 0
	mov	es, bx				; Set target segment
	mov	cx, 2000h			; Clear 8K at a time
	rep	stosw
	add	bh, 2				; Go to the next segment
ifdef	UMA_END
	cmp	bx, UMA_END			; Until we've reached the end
else
	cmp	bx, 0F000h
endif
	jb	@@loop

	pop	es
	ret

endp	clear_upper_memory
endif


;---------------------------------------------------------------------------------------------------
; Check for CTRL+ALT+DEL combination (with gray DEL key) and reboot if pressed
;---------------------------------------------------------------------------------------------------
ifdef	ENHANCED_KEYB
proc	check_ctrl_alt_del	near

	cmp	al, 53h				; DEL pressed?
	jne	@@done				;
	mov	cl, [ds:17h]			; Get keyboard shift status
	test	cl, 00000100b			; CTRL pressed?
	jz	@@done				;
	test	cl, 00001000b			; ALT pressed?
	jz	@@done
	jmp	reboot				; CTRL+ALT+DEL is pressed, so reboot
@@done:
	ret

endp	check_ctrl_alt_del
endif


;---------------------------------------------------------------------------------------------------
; Interrupt Eh - Diskette Controller
;---------------------------------------------------------------------------------------------------
	entry	0EF57h				; Disk interrupt entry
proc	int_E	far

	sti					; Floppy disk attention
	push	ds
	push	ax
	mov	ax, 40h
	mov	ds, ax
	or	[byte ds:3Eh], 10000000b	; Raise "attention" flag
	mov	al, 20h 			; Send end_of_interrupt code
	out	20h, al 			;   to 8259 interrupt chip
	pop	ax
	pop	ds
	iret

nec_status:
	mov	al, 8				; Send a "Request status"
	call	nec_chip			;   to the NEC 765 chip

nec_status_alt:
	push	bx				; Alternate entry point
	push	cx
	mov	cx, 7
	xor	bx, bx

@@status_wait:
	call	nec_ready			; Wait for NEC 765 ready
	jb	@@status_error			;   NEC 765 error
	mov	[bx+42h], al			; Save status in BIOS block
	jz	@@status_ok			;   NEC 765 ready
	inc	bx				; Count more
	loop	@@status_wait
	mov	[byte ds:41h], 20h		; NEC 765 controller error

@@status_error:
	stc					; Set error condition
	pop	cx
	pop	bx
	pop	ax
	mov	al, 0
	retn

@@status_ok:
	pop	cx				; Successful return
	pop	bx
	retn

nec_chip:
	push	cx				; Send control to NEC 765 chip
	push	dx
	push	ax
	xor	cx, cx
	mov	dx, 3F4h			; Load NEC 765 status port

@@nec_wait:
	in	al, dx				; Read NEC 765 status
	or	al, al
	js	@@nec_ready			;   done
	loop	@@nec_wait
	mov	[byte ds:41h], 80h		; Set time out status
	jmp	short @@nec_error

@@nec_ready:
	test	al, 40h 			; Check data direction
	jz	@@nec_data
	mov	[byte ds:41h], 20h		;   NEC 765 is gimped
	jmp	short @@nec_error

@@nec_data:
	inc	dx				; Load NEC 765 data port
	pop	ax
	out	dx, al				;   write user's parameter
	clc
	pop	dx
	pop	cx
nec_return:
	retn

@@nec_error:
	pop	ax				; Common error return
	pop	dx
	pop	cx
	pop	ax
	mov	al, 0
	stc
	retn

endp	int_E


;---------------------------------------------------------------------------------------------------
; Interrupt 1Eh - Diskette Parameter Table
;---------------------------------------------------------------------------------------------------
	entry	0EFC7h				; IBM entry for disk param
proc	int_1E	far

	db	11001111b			; Disk parameter table
	db	2
	db	25h
	db	2
	db	8
	db	2Ah
	db	0FFh
	db	50h
	db	0F6h
	db	19h
	db	4

endp	int_1E


;---------------------------------------------------------------------------------------------------
; Interrupt 17h - Parallel LPT Services
;---------------------------------------------------------------------------------------------------
	entry	0EFD2h				; IBM entry for parallel LPT
proc	int_17	far

	sti					; Parallel printer services
	push	ds
	push	bx
	push	cx
	push	dx
	mov	bx, 40h
	mov	ds, bx
	mov	bx, dx				; dx is printer index (0 - 3)
	shl	bx, 1				;   word index
	mov	dx, [bx+8]			; Load printer port
	or	dx, dx
	jz	@@end				; Goes to black hole
	or	ah, ah
	jz	@@print				; Function is print, ah=0
	dec	ah
	jz	@@init				; Function is init, ah=1
	dec	ah
	jz	@@status			; Get the status, ah=2

@@end:	pop	dx
	pop	cx
	pop	bx
	pop	ds
	iret

@@print:
	out	dx, al				; Char --> data lines 0-7
	inc	dx				; Printer status port
	mov	bh, [bx+78h]			; Load time out parameter
	mov	ah, al

@@retry:
	xor	cx, cx				; Clear low order time out

@@poll: in	al, dx				; Get line printer status
	or	al, al				;   ready?
	js	@@ready				;   done if so
	loop	@@poll
	dec	bh				; Decrement hi order time out
	jnz	@@retry

	or	al, 00000001b			; Set timeout in Status Byte
	and	al, 11111001b			;   bits returned to caller
	jmp	short @@toggle

@@ready:
	inc	dx				; Printer control port
	mov	al, 00001101b			; Set output strobe hi
	out	dx, al				;   data lines 0-7 valid

@@strobe:
	mov	al, 00001100b			; Set output strobe lo
	out	dx, al				;   data lines 0-7 ?????
	dec	dx				; Printer status port
	jmp	short @@get_status		;  get line printer status

@@status:
	mov	ah, al				; Save copy of character
	inc	dx				; Printer status port

@@get_status:
	in	al, dx				; Read printer status
	and	al, 11111000b			;   bits returned to caller

@@toggle:
	xor	al, 01001000b			;   toggle ERROR, ACKNOWLEDGE
	xchg	al, ah
	jmp	@@end				; Exit, ah=status, al=character

@@init: mov	ah, al				; Initialize the line printer
	inc	dx
	inc	dx
	mov	al, 00001000b
	out	dx, al				; Request initialize
	mov	cx, 5DCh			;   delay
@@delay:
	loop	@@delay
	jmp	@@strobe			; Strobe the line printer

endp	int_17


str_cga		db	195, ' CGA Graphics', 0


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Video BIOS (Mono/CGA) Main Entry
;---------------------------------------------------------------------------------------------------
	entry	0F045h				; IBM entry point for table

video_funcs	dw	int_10_func_0		; Set mode
		dw	int_10_func_1		; Set cursor type
		dw	int_10_func_2		; Set cursor position
		dw	int_10_func_3		; Get cursor position
		dw	int_10_func_4		; Read light pen position
		dw	int_10_func_5		; Set active display page
		dw	int_10_func_6_7		; Scroll active page up
		dw	int_10_func_6_7		; Scroll active page down
		dw	int_10_func_8_9_10	; Read attribute/character
		dw	int_10_func_8_9_10	; Write attribute/character
		dw	int_10_func_8_9_10	; Write character only
		dw	int_10_func_11		; Set color
		dw	int_10_func_12		; Write pixel
		dw	int_10_func_13		; Read pixel
		dw	int_10_func_14		; Write teletype
		dw	int_10_func_15		; Return current video state

	entry	0F065h				; IBM entry, video BIOS service
proc	int_10	far

	sti					; Video BIOS service ah=(0-15)
	cld					;   strings auto-increment
	push	bp
	push	es
	push	ds
	push	si
	push	di
	push	dx
	push	cx
	push	bx
	push	ax
	mov	bx, 40h
	mov	ds, bx
	mov	bl, [ds:10h]			; Get equipment byte
	and	bl, 00110000b			;   isolate video mode
	cmp	bl, 00110000b			; Check for monochrome card
	mov	bx, 0B800h
	jnz	@@dispatch			;   not there, bx --> CGA
	mov	bx, 0B000h			; Else bx --> MONO

@@dispatch:
	push	bx				; Save video buffer address
	mov	bp, sp				;   start of stack frame
	call	int_10_dispatch			;   then do the function
	pop	si
	pop	ax
	pop	bx
	pop	cx
	pop	dx
	pop	di
	pop	si
	pop	ds
	pop	es
	pop	bp
	iret

map_byte:
	push	dx				; Multiply al by bx, cx --> buffer
	mov	ah, 0
	mul	bx				; Position in ax
	pop	dx
	mov	cx, [bp+0]			; cx --> video buffer
	retn

endp	int_10


str_last_line	db	192, 0


;---------------------------------------------------------------------------------------------------
; Interrupt 1Dh - Video Parameter Tables
;---------------------------------------------------------------------------------------------------
	entry	0F0A4h				; IBM entry, SET_MODE tables
proc	int_1D	far

	db	38h, 28h, 2Dh, 0Ah, 1Fh, 6, 19h	; Init string for 40x25 color
	db	1Ch, 2, 7, 6, 7
	db	0, 0, 0, 0

	db	71h, 50h, 5Ah, 0Ah, 1Fh, 6, 19h	; Init string for 80x25 color
	db	1Ch, 2, 7, 6, 7
	db	0, 0, 0, 0

	db	38h, 28h, 2Dh, 0Ah, 7Fh, 6, 64h	; Init string for graphics
	db	70h, 2, 1, 6, 7
	db	0, 0, 0, 0

	db	61h, 50h, 52h, 0Fh, 19h, 6, 19h	; Init string for 80x25 b/w
	db	19h, 2, 0Dh, 0Bh, 0Ch
	db	0, 0, 0, 0

regen_len	dw	0800h			; Regen length, 40x25
		dw	1000h			;	        80x25
		dw	4000h			;	        graphics
		dw	4000h

max_cols	db	28h, 28h, 50h, 50h, 28h, 28h, 50h, 50h	; Maximum columns
modes		db	2Ch, 28h, 2Dh, 29h, 2Ah, 2Eh, 1Eh, 29h	; Table of mode sets
mul_lookup	db	00h, 00h, 10h, 10h, 20h, 20h, 20h, 30h	; Table lookup for multiply

endp	int_1D


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Function Dispatch
;---------------------------------------------------------------------------------------------------
proc    int_10_dispatch	near

	cmp	ah, 0Fh 			; Is ah a legal video command?
	jbe	@@ok
	ret					;   error return if not

@@ok:	shl	ah, 1				; Make word value
	mov	bl, ah				;   then set up bx
	mov	bh, 0
	jmp	[word cs:bx+video_funcs]	;   vector to routines

endp	int_10_dispatch


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Function 0: Set mode
;---------------------------------------------------------------------------------------------------
proc	int_10_func_0	near

	mov	al, [ds:10h]			; Set mode of CRT
	mov	dx, 3B4h			;   mono port
	and	al, 00110000b			;   get display type
	cmp	al, 00110000b			;   equal if mono
	mov	al, 1				; Assume mono display
	mov	bl, 7				;   mode is 7
	jz	@@reset				;   Skip if mono, else CGA
	mov	bl, [bp+2]			; bl = mode number (user al)
	mov	dl, 0D4h			; 3D4 is CGA port
	dec	al

@@reset:
	mov	[ds:63h], dx			; Save current CRT display port
	add	dl, 4
	out	dx, al				; Reset the video
	mov	[ds:49h], bl			;   save current CRT mode
	push	ds
	xor	ax, ax
	mov	ds, ax
	les	si, [dword ds:74h]		; si --> INT_1D video parameters
	pop	ds
	mov	bh, 0
	push	bx
	mov	bl, [cs:bx+mul_lookup]		; Get bl for index into INT_1D
	add	si, bx
	mov	cx, 10h 			; Sixteen values to send

@@loop:	mov	al, [es:si]			; Value to send in si
	call	send_ax				;   send it
	inc	ah				;   bump count
	inc	si				;   point to next
	loop	@@loop				;   loop until done

	mov	bx, [bp+0]			; bx --> regen buffer
	mov	es, bx				;   into es segment
	xor	di, di
	call	mode_check			; Set flags to mode
	mov	cx, 2000h			;   assume CGA
	mov	ax, 0				;   and graphics
	jb	@@fill				;   do graphics fill
	jnz	@@text				;   Alphanumeric fill
	mov	cx, 800h			;   mono card
@@text:	mov	ax, 7*100h+' '			; Word for text fill
@@fill:	repz	stosw				;   fill regen buffer

	mov	dx, [ds:63h]			; Get the port
	add	dl, 4
	pop	bx
	mov	al, [cs:bx+modes]		; Load data to set for mode
	out	dx, al				;   and send it
	mov	[ds:65h], al			;   then save active data
	inc	dx
	mov	al, 30h 			; Assume not 640x200 b/w
	cmp	bl, 6				;   correct?
	jnz	@@palette
	mov	al, 3Fh 			; Palette for 640x200 b/w

@@palette:
	mov	[ds:66h], al			;   save palette
	out	dx, al				;   send palette
	xor	ax, ax
	mov	[ds:4Eh], ax			; Start at beg. of 1st page
	mov	[ds:62h], al			;   active page=page 0
	mov	cx, 8				; Do 8 pages of cursor data
	mov	di, 50h 			; Page cursor data at 40:50

@@cursor:
	mov	[di], ax			; Cursor at upper left of page
	inc	di				;   next page
	loop	@@cursor

	mov	al, [cs:bx+max_cols]		; Get display width
	mov	[ds:4Ah], ax			;   save it
	and	bl, 11111110b
	mov	ax, [word cs:bx+regen_len]	; Get video regen length
	mov	[ds:4Ch], ax			;   save it
	ret

endp	int_10_func_0


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Function 1: Set cursor type
;---------------------------------------------------------------------------------------------------
proc	int_10_func_1	near

	mov	cx, [bp+6]			; Set cursor type, from cx
	mov	[ds:60h], cx			;   save it
	mov	ah, 0Ah 			; CRT index register 0Ah
	call	out_6845			;   send ch, cl to CRT register
	ret

endp	int_10_func_1


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Function 2: Set cursor position
;---------------------------------------------------------------------------------------------------
proc	int_10_func_2	near

	mov	bl, [bp+5]			; Set cursor position, page bh
	shl	bl, 1				;   (our bl)
	mov	bh, 0
	mov	ax, [bp+8]			; Position in user dx (our ax)
	mov	[bx+50h], ax			;   remember cursor position
	jmp	set_cursor			;   set 6845 cursor hardware

endp	int_10_func_2


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Function 3: Get cursor position
;---------------------------------------------------------------------------------------------------
proc	int_10_func_3	near

	mov	bl, [bp+5]			; Get cursor position, page bh
	shl	bl, 1
	mov	bh, 0
	mov	ax, [bx+50h]
	mov	[bp+8], ax			;   return position in user dx
	mov	ax, [ds:60h]			; Get cursor mode
	mov	[bp+6], ax			;   return in user cx
	ret

endp	int_10_func_3


pen_offset	db	3, 3, 5, 5, 3, 3, 3, 4	; Light pen offset table


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Function 4: Read light pen position
;---------------------------------------------------------------------------------------------------
proc	int_10_func_4	near

	mov	dx, [ds:63h]
	add	dl, 6
	mov	[byte bp+3], 0			; ah=0, assume not triggered
	in	al, dx
	test	al, 00000100b
	jz	@@reset				; Skip, reset if pen not set
	test	al, 00000010b
	jnz	@@triggered			; Skip if pen triggered
	ret					;   return, do not reset

@@triggered:
	mov	ah, 10h 			; Offset to pen port is 10h
	call	pen_pos				;   read into ch, cl
	mov	bl, [ds:49h]			; Get CRT mode data word
	mov	cl, bl
	mov	bh, 0
	mov	bl, [byte cs:bx+pen_offset]	; Load offset for subtraction
	sub	cx, bx
	jns	@@mode				;   did not overflow
	xor	ax, ax				; Else fudge a zero

@@mode:	call	mode_check			; Set flags on display type
	jnb	@@text				;   text mode, skip
	mov	ch, 28h
	div	dl
	mov	bl, ah
	mov	bh, 0
	mov	cl, 3
	shl	bx, cl
	mov	ch, al
	shl	ch, 1
	mov	dl, ah
	mov	dh, al
	shr	dh, 1
	shr	dh, 1
	cmp	[byte ds:49h], 6		; Mode 640x200 b/w?
	jnz	@@done				;   no, skip
	shl	dl, 1
	shl	bx, 1
	jmp	short @@done

@@text:	div	[byte ds:4Ah]			; Divide by columns in screen
	xchg	al, ah				;   as this is text mode
	mov	dx, ax
	mov	cl, 3
	shl	ah, cl
	mov	ch, ah
	mov	bl, al
	mov	bh, 0
	shl	bx, cl

@@done:	mov	[byte bp+3], 1			; Return ah=1, light pen read
	mov	[bp+8], dx			;   row, column in user dx
	mov	[bp+4], bx			;   pixel column in user bx
	mov	[bp+7], ch			;   raster line in user ch

@@reset:
	mov	dx, [ds:63h]			; Get port of active CRT card
	add	dx, 7
	out	dx, al				;   reset the light pen
	ret

endp	int_10_func_4


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Function 5: Set active display page
;---------------------------------------------------------------------------------------------------
proc	int_10_func_5	near

	mov	al, [bp+2]			; Set active display page to al
	mov	[ds:62h], al			;   save new active page
	mov	ah, 0				;   clear high order
	push	ax
	mov	bx, [ds:4Ch]			; Get size of regen buffer
	mul	bx				;   times number of pages
	mov	[ds:4Eh], ax			; Now ax = CRT offset, save
	shr	ax, 1				;   now word offset
	mov	cx, ax				;   save a copy
	mov	ah, 0Ch 			; CRT index register 0Ch
	call	out_6845			;   send ch, cl through CRT register
	pop	bx
	call	move_cursor			; Save new parameters
	ret

endp	int_10_func_5


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Function 6: Scroll active page up
;                 Function 7: Scroll active page down
;---------------------------------------------------------------------------------------------------
proc	int_10_func_6_7	near

	call	mode_check
	jnb	@@text
	jmp	@@graphics			; Graphics scroll

@@text: cld					; Strings go upward
	cmp	[byte ds:49h], 2
	jb	@@get_coords			;   no retrace wait needed
	cmp	[byte ds:49h], 3
	ja	@@get_coords			;   no retrace wait needed
	mov	dx, 3DAh			; Else 80x25, do the kludge

@@wait: in	al, dx				; Read CGA status register
	test	al, 00001000b			;   vertical retrace?
	jz	@@wait				;   wait until it is
	mov	dx, 3D8h			; Then go and
	mov	al, 25h 			;   turn the display
	out	dx, al				;   off to avoid snow

@@get_coords:
	mov	ax, [bp+8]			; Get row, column of upper left
	push	ax
	cmp	[byte bp+3], 7			; Check for scroll down
	jz	@@offset			;   yes, skip if so
	mov	ax, [bp+6]			; Get row, column of lower right

@@offset:
	call	rc_to_col			; Get byte offset in CRT buffer
	add	ax, [ds:4Eh]			;   add base for CRT buffer
	mov	si, ax
	mov	di, ax
	pop	dx
	sub	dx, [bp+6]			; Subtract (row, col) lwr rhgt
	add	dx, 101h			;   width of one char
	mov	bx, [ds:4Ah]			; Get columns in display
	shl	bx, 1				;   bytes in row of display
	push	ds
	mov	al, [bp+2]			; Get scroll fill character
	call	map_byte			;   calculate offset
	mov	es, cx				; cx --> byte in buffer
	mov	ds, cx
	cmp	[byte bp+3], 6			; Scroll up?
	jz	@@count				;   skip if so
	neg	ax
	neg	bx
	std					; Else start at top of page

@@count:
	mov	cl, [bp+2]			; Get count of lines to scroll
	or	cl, cl
	jz	@@attr				;   nothing to do
	add	si, ax
	sub	dh, [bp+2]

@@scroll:
	mov	ch, 0				; Clear high order word count
	mov	cl, dl				;   load low order word count
	push	di
	push	si
	repz	movsw				; Do the scroll
	pop	si
	pop	di
	add	si, bx				; Move one line in direction
	add	di, bx				;	 ""	  ""
	dec	dh				; One less line to scroll
	jnz	@@scroll
	mov	dh, [bp+2]			; Now get number of rows

@@attr: mov	ch, 0				; Clear high order word count
	mov	ah, [bp+5]			;   get fill attribute
	mov	al, ' ' 			;   fill character

@@fill: mov	cl, dl				; Get characters to scroll
	push	di
	repz	stosw				;   store fill attr/char
	pop	di
	add	di, bx				; Show row was filled
	dec	dh
	jnz	@@fill				;   more rows are left
	pop	ds
	call	mode_check			; Check for monochrome card
	jz	@@done				;   skip if so
	mov	al, [ds:65h]			; Get the mode data byte
	mov	dx, 3D8h			;   load active CRT card port
	out	dx, al				;   and unblank the screen

@@done: ret

@@graphics:
	cld					; Assume graphics scroll up
	mov	ax, [bp+8]			; (Row, Col) of lower right
	push	ax
	cmp	[byte bp+3], 7			; Scroll down?
	jz	@@gfx_offset			;   skip if so
	mov	ax, [bp+6]			; (Row, Col) of upper left

@@gfx_offset:
	call	gfx_rc_col			; Convert (Row, Col) -> Chars
	mov	di, ax
	pop	dx
	sub	dx, [bp+6]			; Chars to copy over
	add	dx, 101h			;   width of one char
	shl	dh, 1
	shl	dh, 1
	mov	al, [bp+3]			; Get command type
	cmp	[byte ds:49h], 6		;   is this 640x200?
	jz	@@gfx_next			;   skip if so
	shl	dl, 1				; Else bigger characters
	shl	di, 1
	cmp	al, 7				; Is this scroll down?
	jnz	@@gfx_next			;   skip if not so
	inc	di

@@gfx_next:
	cmp	al, 7				; Is this scroll down?
	jnz	@@gfx_start			;   skip if not so
	add	di, 0F0h

@@gfx_start:
	mov	bl, [bp+2]			; Number of rows to blank
	shl	bl, 1
	shl	bl, 1
	push	bx
	sub	dh, bl				; Subtract from row count
	mov	al, 50h
	mul	bl
	mov	bx, 1FB0h
	cmp	[byte bp+3], 6			; Is this scroll up?
	jz	@@gfx_end			;   skip if so
	neg	ax				; Else do it
	mov	bx, 2050h
	std					;   in reverse

@@gfx_end:
	mov	si, di				; End of area
	add	si, ax				;   start
	pop	ax
	or	al, al
	mov	cx, [bp+0]
	mov	ds, cx
	mov	es, cx
	jz	@@gfx_attr			; No rows to scroll
	push	ax

@@gfx_scroll:
	mov	ch, 0				; Zero hi order byte count
	mov	cl, dl				;   bytes in row
	push	si
	push	di
	repz	movsb				; Copy one plane
	pop	di
	pop	si
	add	si, 2000h			; Load other graphics
	add	di, 2000h			;   video plane
	mov	cl, dl
	push	si
	push	di
	repz	movsb				; Copy other plane
	pop	di
	pop	si
	sub	si, bx
	sub	di, bx
	dec	dh				; One less row to scroll
	jnz	@@gfx_scroll			;   loop if more to do
	pop	ax
	mov	dh, al				; Load rows to blank

@@gfx_attr:
	mov	al, [bp+5]			; Get fill attribute
	mov	ch, 0

@@gfx_fill:
	mov	cl, dl				; Get bytes per row
	push	di
	repz	stosb				; Load row with fill attribute
	pop	di
	add	di, 2000h			; Do other graphics video plane
	mov	cl, dl
	push	di
	repz	stosb				; Load row with fill attribute
	pop	di
	sub	di, bx
	dec	dh				; Show one less row to blank
	jnz	@@gfx_fill			;   loop if more to do
	ret

endp	int_10_func_6_7


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Function 8: Read attribute/character
;                 Function 9: Write attribute/character
;                 Function 10: Write character only
;---------------------------------------------------------------------------------------------------
proc	int_10_func_8_9_10	near

	call	mode_check
	jb	@@graphics			; Graphics operation
	mov	bl, [bp+5]			; Get the display page
	mov	bh, 0
	push	bx
	call	text_rc_col			; Convert Row, Col, Page -> Col
	mov	di, ax				;   offset in di
	pop	ax
	mul	[word ds:4Ch]			; Page length X page number
	add	di, ax				;   current char position
	mov	si, di				;   move into si
	mov	dx, [ds:63h]			; Display port into dx
	add	dx, 6				;   get status port
	push	ds
	mov	bx, [bp+0]			; bx --> regen. buffer
	mov	ds, bx
	mov	es, bx
	mov	al, [bp+3]			; Get user (ah) function request
	cmp	al, 8
	jnz	@@write				;   skip if not read attribute

@@read:
	in	al, dx				; Read CRT display status
	test	al, 00000001b			;   test for horizontal retrace
	jnz	@@read				; Yes, wait for display on
	cli					;   no interrupts now

@@read_wait:
	in	al, dx				; Read CRT display status
	test	al, 00000001b			;   test for horizontal retrace
	jz	@@read_wait			;   not yet, wait for it

	lodsw					; Read character/attribute
	pop	ds
	mov	[bp+2], al			; Return character
	mov	[bp+3], ah			;   and attribute
	ret

@@write:
	mov	bl, [bp+2]			; Get character to write
	mov	bh, [bp+4]			;   attribute
	mov	cx, [bp+6]			;   character count
	cmp	al, 0Ah 			; Write character only?
	jz	@@char_write			;   skip if so

@@write_loop:
	in	al, dx				; Read CRT display status
	test	al, 00000001b			;   test for horizontal retrace
	jnz	@@write_loop			; Yes, wait for display on
	cli					;   no interrupts now

@@write_wait:
	in	al, dx				; Read CRT display status
	test	al, 00000001b			;   test for horizontal retrace
	jz	@@write_wait			;   not yet, wait for it

	mov	ax, bx				; Get char/attribute
	stosw					;   write it
	loop	@@write_loop			;   loop for character count
	pop	ds
	ret

@@char_write:
	in	al, dx				; Read CRT display status
	test	al, 00000001b			;   test for horizontal retrace
	jnz	@@char_write			;   not yet, wait for it
	cli					;   no interrupts now

@@char_wait:
	in	al, dx				; Read CRT display status
	test	al, 00000001b			;   test for horizontal retrace
	jz	@@char_wait			;   not yet, wait for it

	mov	al, bl				; Get character
	stosb					;   write it
	inc	di				;   skip attribute
	loop	@@char_write			;   loop for character count
	pop	ds
	ret

@@graphics:
	cmp	[byte bp+3], 8			; Read graphics char/attr?
	jnz	@@gfx_write			;   no, must be write
	jmp	@@gfx_read			; Else read char/attr

@@gfx_write:
	mov	ax, [ds:50h]			; Get cursor position
	call	gfx_rc_col			;   convert (row, col) -> col
	mov	di, ax				; Save in displacement register
	push	ds
	mov	al, [bp+2]			; Get character to write
	mov	ah, 0
	or	al, al				; Is it user character set?
	js	@@user_chars			;   skip if so
	mov	dx, cs				; Else use ROM character set
	mov	si, offset gfx_chars		;   offset gfx_chars into si
	jmp	short @@buffer

@@user_chars:
	and	al, 7Fh 			; Origin to zero
	xor	bx, bx				;   then go load
	mov	ds, bx				;   user graphics
	lds	si, [dword ds:7Ch]		;   vector, offset in si
	mov	dx, ds				;   segment into dx

@@buffer:
	pop	ds				; Restore data segment
	mov	cl, 3				;   char 8 pixels wide
	shl	ax, cl
	add	si, ax				; Add regen buffer base address
	mov	ax, [bp+0]			;   get regen buffer address
	mov	es, ax				;   into es
	mov	cx, [bp+6]			;   load character count
	cmp	[byte ds:49h], 6		; Is the mode 640x200 b/w?
	push	ds
	mov	ds, dx
	jz	@@write_640x200			;   skip if so
	shl	di, 1
	mov	al, [bp+4]			; Get character attribute
	and	ax, 3
	mov	bx, 5555h
	mul	bx
	mov	dx, ax
	mov	bl, [bp+4]

@@gfx_write_loop:
	mov	bh, 8				; Char 8 pixels wide
	push	di
	push	si

@@write_read:
	lodsb					; Read the screen
	push	cx
	push	bx
	xor	bx, bx
	mov	cx, 8

@@shift:
	shr	al, 1				; Shift bits through byte
	rcr	bx, 1
	sar	bx, 1
	loop	@@shift

	mov	ax, bx				; Result into ax
	pop	bx
	pop	cx
	and	ax, dx
	xchg	ah, al
	or	bl, bl
	jns	@@write_word
	xor	ax, [es:di]

@@write_word:
	mov	[es:di], ax			; Write new word
	xor	di, 2000h
	test	di, 2000h			; Is this other plane?
	jnz	@@write_next			;   nope
	add	di, 50h 			; Else advance character

@@write_next:
	dec	bh				; Show another char written
	jnz	@@write_read			;   more to go
	pop	si
	pop	di
	inc	di
	inc	di
	loop	@@gfx_write_loop
	pop	ds
	ret

@@write_640x200:
	mov	bl, [bp+4]			; Get display page
	mov	dx, 2000h			;   size of graphics plane

@@write_loop_640:
	mov	bh, 8				; Pixel count to write
	push	di
	push	si

@@write_read_640:
	lodsb					; Read from one plane
	or	bl, bl				;   done both planes?
	jns	@@write_byte_640		;   skip if not
	xor	al, [es:di]			; Else load attribute

@@write_byte_640:
	mov	[es:di], al			; Write out attribute
	xor	di, dx				;   get other plane
	test	di, dx				; Done both planes?
	jnz	@@write_next_640		;   skip if not
	add	di, 50h 			; Else position for now char

@@write_next_640:
	dec	bh				; Show row of pixels read
	jnz	@@write_read_640		;   not done all of them
	pop	si
	pop	di
	inc	di
	loop	@@write_loop_640
	pop	ds
	ret

@@gfx_read:
	cld					; Increment upwards
	mov	ax, [ds:50h]			;   get cursor position
	call	gfx_rc_col			; Convert (row, col) -> columns
	mov	si, ax				;   save in si
	sub	sp, 8				; Grab 8 bytes temp storage
	mov	di, sp				;   save base in di
	cmp	[byte ds:49h], 6		; Mode 640x200 b/w?
	mov	ax, [bp+0]			;   ax --> CRT regen buffer
	push	ds
	push	di
	mov	ds, ax
	jz	@@640x200			; Mode is 640x200 b/w - skip
	mov	dh, 8				; Eight pixels high/char
	shl	si, 1
	mov	bx, 2000h			; Bytes per video plane

@@read_loop:
	mov	ax, [si]			; Read existing word
	xchg	ah, al
	mov	cx, 0C000h			; Attributes to scan for
	mov	dl, 0

@@attr: test	ax, cx				; Look for attributes
	clc
	jz	@@skip				;   set, skip
	stc					; Else show not set

@@skip: rcl	dl, 1
	shr	cx, 1
	shr	cx, 1
	jnb	@@attr				;   more shifts to go
	mov	[ss:di], dl
	inc	di
	xor	si, bx				; Do other video plane
	test	si, bx				;   done both planes?
	jnz	@@row_done			;   no, skip
	add	si, 50h 			; Else advance pointer

@@row_done:
	dec	dh				; Show another pixel row done
	jnz	@@read_loop			;   more rows to do
	jmp	short @@load_chars

@@640x200:
	mov	dh, 4				; Mode 640x200 b/w - special

@@read_plane:
	mov	ah, [si]			; Read pixels from one plane
	mov	[ss:di], ah			;   save on stack
	inc	di				;   advance
	mov	ah, [si+2000h]			; Read pixels from other plane
	mov	[ss:di], ah			; Save pixels on stack
	inc	di				;   advance
	add	si, 50h 			; Total pixels in char
	dec	dh				;   another row processed
	jnz	@@read_plane			;   more to do

@@load_chars:
	mov	dx, cs				; Load segment of graphics char
	mov	di, offset gfx_chars		;   and offset
	mov	es, dx				;   save offset in es
	mov	dx, ss
	mov	ds, dx
	pop	si
	mov	al, 0

@@gfx_user_chars:
	mov	dx, 80h 			; Number of characters in graphics set

@@gfx_read_loop:
	push	si
	push	di
	mov	cx, 8				; Bytes to compare for char
	repz	cmpsb				;   do compare
	pop	di
	pop	si
	jz	@@read_done			; Found graphics character
	inc	al				;   else show another char
	add	di, 8				;   advance one row
	dec	dx				;   one less char to scan
	jnz	@@gfx_read_loop			; Loop if more char left

	or	al, al				; User graphics character set?
	jz	@@read_done			;   no, not found
	xor	bx, bx
	mov	ds, bx
	les	di, [dword ds:7Ch]		; Else load user graphics char
	mov	bx, es
	or	bx, di
	jz	@@read_done			;   not found
	jmp	@@gfx_user_chars		; Try using user graphics char

@@read_done:
	mov	[bp+2], al			; Return char in user al
	pop	ds
	add	sp, 8				;   return temp storage
	ret

endp	int_10_func_8_9_10


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Function 11: Set color
;---------------------------------------------------------------------------------------------------
proc	int_10_func_11	near

	mov	dx, [ds:63h]			; Set color, get CGA card port
	add	dx, 5				;   color select register
	mov	al, [ds:66h]			; Get CRT palette
	mov	ah, [bp+5]			;   new palette ID, user bh
	or	ah, ah
	mov	ah, [bp+4]			;   new palette color, user bl
	jnz	@@skip				; Palette ID specified, skip
	and	al, 0E0h
	and	ah, 1Fh 			; Null ID = ID 01Fh
	or	al, ah				;   set in color
	jmp	short @@new_palette

@@skip: and	al, 0DFh
	test	ah, 1
	jz	@@new_palette
	or	al, 20h

@@new_palette:
	mov	[ds:66h], al			; Save new palette
	out	dx, al				;   tell CGA about it
	ret

endp	int_10_func_11


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Function 12: Write pixel
;---------------------------------------------------------------------------------------------------
proc	int_10_func_12	near

	mov	ax, [bp+0]			; Write pixel
	mov	es, ax
	mov	dx, [bp+8]			; Load row from user dx
	mov	cx, [bp+6]			;   col from user cx
	call	dot_offset			; Find dot offset
	jnz	@@ok				;   valid
	mov	al, [bp+2]			; Load user color
	mov	bl, al
	and	al, 1
	ror	al, 1
	mov	ah, 7Fh
	jmp	short @@read

@@ok:	shl	cl, 1
	mov	al, [bp+2]
	mov	bl, al
	and	al, 3
	ror	al, 1
	ror	al, 1
	mov	ah, 3Fh

@@read:	ror	ah, cl
	shr	al, cl
	mov	cl, [es:si]			; Read the char with the dot
	or	bl, bl
	jns	@@color
	xor	cl, al				; Exclusive or existing color
	jmp	short @@write

@@color:
	and	cl, ah				; Set new color for dot
	or	cl, al

@@write:
	mov	[es:si], cl			; Write out char with the dot
	ret

endp	int_10_func_12


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Function 13: Read pixel
;---------------------------------------------------------------------------------------------------
proc	int_10_func_13	near

	mov	ax, [bp+0]			; ax --> video regen buffer
	mov	es, ax				;   into es segment
	mov	dx, [bp+8]			; Load row from user dx
	mov	cx, [bp+6]			;   col from user cx
	call	dot_offset			; Calculate dot offset
	mov	al, [es:si]			;   read dot
	jnz	@@offset			;   was there
	shl	al, cl
	rol	al, 1
	and	al, 1
	jmp	short @@done

@@offset:
	shl	cl, 1				; Calculate offset in char
	shl	al, cl
	rol	al, 1
	rol	al, 1
	and	al, 3

@@done:	mov	[bp+2], al			; Return dot pos in user al
	ret

endp	int_10_func_13


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Function 14: Write teletype
;---------------------------------------------------------------------------------------------------
proc	int_10_func_14	near

	mov	bl, [ds:62h]			; Get active video page (0-7)
	shl	bl, 1				;   as word index
	mov	bh, 0				;   clear high order
	mov	dx, [bx+50h]			; Index into cursor position

	mov	al, [bp+2]			; Get character to write
	cmp	al, 8				;   back space?
	jz	@@back_space			;   skip if so
	cmp	al, LF				; Is it a line feed?
	jz	@@line_feed			;   skip if so
	cmp	al, 7				; Print a bell?
	jz	@@beep				;   do beep
	cmp	al, CR				; Is it a carriage return?
	jz	@@carriage_return		;   skip if so
	mov	bl, [bp+4]			; Else write at cursor position
	mov	ah, 0Ah
	mov	cx, 1				;   one time
	int	10h
	inc	dl				; Advance cursor
	cmp	dl, [ds:4Ah]			;   check for line overflow
	jnz	@@position
	mov	dl, 0				; Overflowed, then fake
	jmp	short @@line_feed		;   new line

@@back_space:
	cmp	dl, 0				; At start of line?
	jz	@@position			;   skip if so
	dec	dl				; Else back up
	jmp	short @@position		;   join common code

@@beep:	mov	bl, 1				; Do a short
	call	beep				;   beep
	ret

@@carriage_return:
	mov	dl, 0				; Position to start of line

@@position:
	mov	bl, [ds:62h]			; Get active video page (0-7)
	shl	bl, 1				;   as word index
	mov	bh, 0				;   clear high order
	mov	[bx+50h], dx			; Remember the cursor position
	jmp	set_cursor			;   set 6845 cursor hardware

@@line_feed:
	cmp	dh, 18h 			; Done all 24 lines on page?
	jz	@@scroll			;   yes, scroll
	inc	dh				; Else advance line
	jnz	@@position

@@scroll:
	mov	ah, 2				; Position cursor at line start
	int	10h
	call	mode_check			; Is this text mode?
	mov	bh, 0
	jb	@@scroll_up			; Skip if text mode
	mov	ah, 8
	int	10h				;   else read attribute
	mov	bh, ah

@@scroll_up:
	mov	ah, 6				; Now prepare to
	mov	al, 1				;   scroll
	xor	cx, cx				;   the
	mov	dh, 18h 			;   page
	mov	dl, [ds:4Ah]			;   up
	dec	dl
	int	10h
	ret

endp	int_10_func_14


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Function 15: Return current video state
;---------------------------------------------------------------------------------------------------
proc	int_10_func_15	near

	mov	al, [ds:4Ah]			; Get current video state
	mov	[bp+3], al			;   columns
	mov	al, [ds:49h]
	mov	[bp+2], al			;   mode
	mov	al, [ds:62h]
	mov	[bp+5], al			;   page
	ret

endp	int_10_func_15


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Internal: Video mode check
;---------------------------------------------------------------------------------------------------
proc	mode_check	near

	push	ax				; Set flags to current mode
	mov	al, [ds:49h]			;   get mode
	cmp	al, 7				;   equal if mono
	jz	@@done
	cmp	al, 4
	cmc
	jnb	@@done				;   carry set on graphics
	sbb	al, al
	stc

@@done: pop	ax
	ret

endp	mode_check


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Internal: Calculate dot offset
;---------------------------------------------------------------------------------------------------
proc	dot_offset	near

	mov	al, 50h 			; Dots in character position
	xor	si, si
	shr	dl, 1				; Two bytes/char position
	jnb	@@calc				;   no overflow
	mov	si, 2000h			; Else on other video plane

@@calc: mul	dl				; Multiply position by row
	add	si, ax				;   add in column position
	mov	dx, cx				; Copy column position
	mov	cx, 302h			;   regular char size
	cmp	[byte ds:49h], 6		; Mode 640x200, b/w?
	pushf
	jnz	@@done				;   skip if not
	mov	cx, 703h			; Else special char size

@@done: and	ch, dl
	shr	dx, cl
	add	si, dx
	xchg	cl, ch
	popf
	ret

endp	dot_offset


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Internal: Read light pen position
;---------------------------------------------------------------------------------------------------
proc	pen_pos	near

	call	@@pen_xy			; Read light pen position high
	mov	ch, al				;   save in ch
	inc	ah
	call	@@pen_xy			; Read light pen position low
	mov	cl, al				;   save in cl
	ret

@@pen_xy:
	push	dx				; Read CRT register offset al
	mov	dx, [ds:63h]			;   get active CRT port
	xchg	al, ah
	out	dx, al				; Send initialization byte
	inc	dl				;   increment
	in	al, dx				; Read pen position byte back
	pop	dx
	ret

endp	pen_pos


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Internal: Convert (row, col) coordinates to column count for text modes
;---------------------------------------------------------------------------------------------------
proc	text_rc_col	near

	mov	bh, 0				; Convert Row, Col, Page -> Col
	shl	bx, 1				;   two bytes/column
	mov	ax, [bx+50h]			; Get page number in ax
						;   join common code
rc_to_col:
	push	bx				; Map (ah=row, al=col) to col
	mov	bl, al
	mov	al, ah
	mul	[byte ds:4Ah]			; Multiply Row x (Row/Column)
	mov	bh, 0
	add	ax, bx				;   add in existing col
	shl	ax, 1				;   times 2 because 2 bytes/col
	pop	bx
	ret

endp	text_rc_col


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Internal: Convert (row, col) coordinates to column count for graphics modes
;---------------------------------------------------------------------------------------------------
proc	gfx_rc_col	near

	push	bx				; Convert (row, col) -> col
	mov	bl, al				;   save column
	mov	al, ah				;   get row
	mul	[byte ds:4Ah]			; Multiply by columns/row
	shl	ax, 1
	shl	ax, 1
	mov	bh, 0
	add	ax, bx				; Add in columns
	pop	bx
	ret

endp	gfx_rc_col


;---------------------------------------------------------------------------------------------------
; Interrupt 10h - Internal: Set 6845 cursor position
;---------------------------------------------------------------------------------------------------
proc	set_cursor	near

	shr	bl, 1				; Sets 6845 cursor position
	cmp	[ds:62h], bl			;   is this page visible?
	jnz	@@done				; No, do nothing in hardware

move_cursor:
	call	text_rc_col			; Map row, col, page to col
	add	ax, [ds:4Eh]			;   + byte offset, regen register
	shr	ax, 1
	mov	cx, ax
	mov	ah, 0Eh 			; Tell 6845 video controller
						;   to position the cursor
out_6845:
	mov	al, ch				; Send ch, cl through CRT register ah
	call	send_ax				;   send ch
	inc	ah				;   increment
	mov	al, cl				;   send cl

send_ax:
	push	dx
	mov	dx, [ds:63h]			; Load active video port
	xchg	al, ah
	out	dx, al				; Send high order
	xchg	al, ah
	inc	dl
	out	dx, al				;   low order
	pop	dx

@@done: ret

endp	set_cursor


;--------------------------------------------------------------------------------------------------
; Slows the system clock rate while accessing the floppy drive
;--------------------------------------------------------------------------------------------------
ifdef	SLOW_FLOPPY				; Run floppy at SLOWEST speed
proc	floppy_speed	near

	in	al, 61h 			; Toggle speed on Floppy Disk
	push	ax				;   save old clock rate
	and	al, 11110011b			;   load slowest clock rate
	out	61h, al 			;   slow down to 4.77 mHz
	call	floppy_exec			; Execute the I/O request
	pop	ax				;   restore old clock rate
	out	61h, al 			;   from saved clock byte
	ret

endp	floppy_speed
endif


;--------------------------------------------------------------------------------------------------
; Give user option to boot ROM BASIC if present, otherwise display "No ROM BASIC" message
;--------------------------------------------------------------------------------------------------
proc	boot_basic	near

	xor	cx, cx
	mov	es, cx
	mov	cx, [es:62h]			; Get int 18h (BASIC) segment in cx

	xor	bl, bl
	add	bh, 3
	mov	ax, bx
	call	locate				; Locate cursor

	mov	si, offset str_no_basic		; Assume no BASIC
	xor	dl, dl

	cmp	cx, 0F600h			; If ROM BASIC is present segment will be F600h
	jne	@@skip				; No BASIC

	mov	si, offset str_boot_basic	; ROM BASIC present
	inc	dl

@@skip:
	call	print				; Display "No BASIC" or "Boot BASIC" message

	sti					; Enable interrupts so timer can run
	mov	bx, BOOT_DELAY * 18		; Get ticks to pause at 18.2 Hz
	add	bx, [es:46Ch]			; Get current timer ticks (0000:046C = 0040:006C)

@@delay:
	mov	ah, 01h
	int	16h				; Check for keypress
	jnz	@@keypress			; End pause if key pressed

	mov	cx, [es:46Ch]			; Get current ticks
	sub	cx, bx				; See if pause is up yet
	jc	@@delay				; Nope

@@done:
	cli					; Disable interrupts
	ret

@@keypress:
	xor	ah, ah
	int	16h				; Flush keystroke from buffer

	or	dl, dl				; Is ROM BASIC present?
	jz	@@done				; No so don't even try

	cmp	al, ' '				; Was the keystroke a space?
	je	@@basic				; Yes, boot BASIC
	jmp	short @@done			; Otherwise return

@@basic:
	int	18h				; Boot ROM BASIC

endp	boot_basic


str_system	db	'System ', 194, ' ', 0
str_8088	db	'8088 CPU (', 0
str_v20		db	'V20 CPU (', 0
str_no_fpu	db	'No FPU)', 0
str_8087	db	'8087 FPU)', 0
str_boot_basic	db	'Press SPACE to boot ROM BASIC...', 0


;---------------------------------------------------------------------------------------------------
; Interrupt 12h - Memory Size
;---------------------------------------------------------------------------------------------------
	entry	0F841h				; IBM entry for memory size
proc	int_12	far

	sti					; Kbytes of memory present
	push	ds
	mov	ax, 40h
	mov	ds, ax
	mov	ax, [ds:13h]			; ax = memory size, kilobytes
	pop	ds
	iret

endp	int_12


;---------------------------------------------------------------------------------------------------
; Interrupt 11h - Equipment Check
;---------------------------------------------------------------------------------------------------
	entry	0F84Dh				; IBM entry for equipment check
proc	int_11	far

	sti					; Equipment present
	push	ds
	mov	ax, 40h
	mov	ds, ax
	mov	ax, [ds:10h]			; ax = equipment byte contents
	pop	ds
	iret

endp	int_11


;---------------------------------------------------------------------------------------------------
; Interrupt 15h - Cassette
;---------------------------------------------------------------------------------------------------
	entry	0F859h				; IBM entry for cassette interrupt
proc	int_15	far

	stc					; Cassette service (error ret)
	mov	ah, 86h
	retf	2

endp	int_15


;---------------------------------------------------------------------------------------------------
; Interrupt 2h - Non-Maskable Interrupt
;---------------------------------------------------------------------------------------------------
	entry	0F85Fh				; IBM non-maskable interrupt entry
proc	int_2	far

	push	ax				; Non-maskable interrupt
	in	al, 62h
	test	al, 11000000b			; Get cause of interrupt
	jnz	@@parity			;   parity error
	jmp	@@end				;   math coprocessor (?)

@@parity:
	push	bx				; Parity error bomb
	push	cx
	push	dx
	push	si
	push	di
	push	bp
	push	ds
	push	es
	mov	ax, 40h 			; Load data segment
	mov	ds, ax
	call	video_init			;   clear/init screen
	push	ds
	push	cs				; Point ds at ROM
	pop	ds
	mov	si, offset str_parity_error	; si --> Parity message
	call	print				;   print
	pop	ds				;   restore ds
	mov	ax, 11h 			; Back cursor over ? marks
	call	locate				;   with call
	mov	al, 0
	out	0A0h, al			;   disable NMI interrupts
	mov	dx, 61h
	in	al, dx				; Get machine flags
	or	al, 00110000b			;   disable parity int
	out	dx, al				; Put out new flags
	and	al, 11001111b			;   enable parity int
	out	dx, al				; Put out new flags
	mov	cl, 6
	mov	bx, [ds:13h]			; Get memory size (K bytes)
	shl	bx, cl
	inc	dx				;   now paragraphs
	xor	ax, ax
	mov	ds, ax

@@next_para:
	mov	cx, 10h 			; Iterations to check
	xor	si, si

@@next_byte:
	mov	ah, [si]			; Read the byte (dummy)
	in	al, dx				;   and read status
	test	al, 11000000b			;   to see what happened
	jnz	@@display_addr			; Read caused parity error
	inc	si				;   else advance pointer
	loop	@@next_byte			;   and try next byte

	mov	ax, ds
	inc	ax				;   next paragraph
	mov	ds, ax
	cmp	ax, bx
	jnz	@@next_para			; More paragraphs to check
	jmp	short @@prompt			;   else flakey error

@@display_addr:
	mov	[si], ah			; Save offset in paragraph
	mov	ax, ds
	call	double_number			; Print segment
	mov	ax, si
	call	digit				; Print offset

@@prompt:
	mov	ax, 16h 			; Where to position cursor
	call	locate				;   position cursor
	push	ds
	push	cs
	pop	ds
	mov	si, offset str_continue		; Continue ?
	call	print				;   ask the user
	pop	ds
	in	al, 21h 			; Get interrupt masks
	push	ax				;   save them
	mov	al, 11111100b
	out	21h, al 			; Disable all but keyboard
	sti					;   enable interrupt system
	call	get_key				; Get keyboard character
	push	ax				;   save it
	call	out_char			; Print ascii character
	pop	ax				;   restore
	cmp	al, 'Y' 			; User wants to continue?
	jz	@@continue			;   continue
	cmp	al, 'y' 			; Look for little case "y"
	jz	@@continue			;   continue
	jmp	cold_boot			; Retry on cold reboot

@@continue:
	call	clear_screen			; Clear display
	pop	ax
	out	21h, al 			; Restore interrupt system state
	mov	dx, 61h 			; Dismiss the NMI interrupt
	in	al, dx				;   read in machine flags
	or	al, 00110000b
	out	dx, al				; Write out, parity disabled
	and	al, 11001111b			;   clears parity error
	out	dx, al				; Write out, parity enabled
	mov	al, 80h
	out	0A0h, al			; Enable NMI interrupts
	pop	es
	pop	ds
	pop	bp
	pop	di
	pop	si
	pop	dx
	pop	cx
	pop	bx

@@end:
	pop	ax
	iret

endp	int_2


lpt_ports	dw	03BCh, 0378h, 0278h	; Possible line printer ports

str_serial	db	195, ' Serial Port at ', 0

str_parity_error	db	'Parity error at: ?????', 0
str_continue		db	CR, LF, 'Continue? ', 0


;--------------------------------------------------------------------------------------------------
; Display al as hex digit in ASCII
;--------------------------------------------------------------------------------------------------
proc	digit	near

	push	ax				; Print hex digit in al
	and	al, 0Fh
	cmp	al, 9
	jbe	@@low
	add	al, 'A'-'9'-1
@@low:
	add	al, '0' 			; Make ascii digit
	call	out_char			;   print it
	pop	ax
	ret

endp	digit


;--------------------------------------------------------------------------------------------------
; Display value in al as 2-character ASCII hex number
;--------------------------------------------------------------------------------------------------
proc	number	near

	push	ax				; Save number
	mov	cl, 4
	shr	al, cl
	call	digit				; Out first digit
	pop	ax
	call	digit				; Out second digit
	ret

endp	number


;--------------------------------------------------------------------------------------------------
; Display value in ax as 3-character ASCII hex number
;--------------------------------------------------------------------------------------------------
proc	big_number	near

	push	ax				; Unsigned word
	mov	al, ah
	call	digit
big_number_entry:
	pop	ax
	call	number
	ret

endp	big_number


;--------------------------------------------------------------------------------------------------
; Display character
;--------------------------------------------------------------------------------------------------
proc	out_char	near

	push	bx
	push	ax
	mov	ah, 0Eh 			; Teletype print service
	mov	bl, 7				;   normal intensity
	int	10h
	pop	ax
	pop	bx
	ret

endp	out_char


;--------------------------------------------------------------------------------------------------
; Display null-terminated string (si)
;--------------------------------------------------------------------------------------------------
proc	print	near

@@loop:
	lodsb					; Print zero terminated string
	or	al, al				; Terminator in ax?
	jz	@@done
	call	out_char			; Print character in ax
	jmp	@@loop				;   back for more
@@done:
	ret

endp	print


;--------------------------------------------------------------------------------------------------
; Positions display cursor
;--------------------------------------------------------------------------------------------------
proc	locate	near

	push	dx
	push	bx
	mov	dx, ax				; Get position for cursor
	mov	ah, 2
	mov	bh, 0				;   page 0
	int	10h
	pop	bx
	pop	dx
	ret

endp	locate


;--------------------------------------------------------------------------------------------------
; Display null-terminated string (si) in color for BIOS title bar
;--------------------------------------------------------------------------------------------------
proc	color_print	near

	mov	bx, 0070h			; Mono uses inverse attribute
	cmp	[byte es:49h], 7		; Get CRT mode
	je	@@loop				;   monochrome
	mov	bx, 001Fh			; Color uses white on blue

@@loop:
	mov	cx, 1
	lodsb					; Print zero terminated string
	or	al, al
	jz	@@done				; Terminator in ax?
	call	color_out_char			; Print character in ax
	jmp	@@loop				;   back for more

@@done:
	mov	cx, 81 - (offset str_banner_end - offset str_banner)	; Extend color bar

color_out_char:
	mov	ah, 09h 			; Write character and attribute
	int	10h

	mov	ah, 03h				; Get cursor position
	int	10h

	mov	ah, 02h				; Set cursor position
	inc	dl				; Advance cursor 1 space
	int	10h

	ret

endp	color_print


;--------------------------------------------------------------------------------------------------
; Initialize video card
;--------------------------------------------------------------------------------------------------
proc	video_init	near

	mov	ah, [ds:10h]			; Get equipment byte
	and	ah, 00110000b			;   extract CRT
	mov	al, 0				;   null low
	cmp	ah, 00110000b			; Monochrome?
	jz	@@init				;   yes
	mov	al, 1				; CGA 40 x 25?
	cmp	ah, 00010000b			;   yes
	jz	@@init				; CGA 80 x 25?
	mov	al, 3				;   yes
@@init:
	mov	ah, 0				; Setup subfunction
	int	10h				;   to video
	ret

endp	video_init


;--------------------------------------------------------------------------------------------------
; Waits for a keypress and then returns it (ah=scan code, al=ASCII)
;--------------------------------------------------------------------------------------------------
proc	get_key	near

	mov	ah, 0				; Read keyboard key
	int	16h
	ret

endp	get_key


;--------------------------------------------------------------------------------------------------
; PC speaker beep (length in bl)
;--------------------------------------------------------------------------------------------------
proc	beep	near

	push	ax
	push	cx
	mov	al, 10110110b			; Timer IC 8253 square waves
	out	43h, al 			;   channel 2, speaker
	mov	ax, 528h			; Get countdown constant word
	out	42h, al 			;   send low order
	mov	al, ah				;   load high order
	out	42h, al 			;   send high order
	in	al, 61h 			; Read IC 8255 machine status
	push	ax
	or	al, 00000011b
	out	61h, al 			; Turn speaker on
	xor	cx, cx
@@delay:
	loop	@@delay
	dec	bl
	jnz	@@delay
	pop	ax
	out	61h, al 			; Turn speaker off
	pop	cx
	pop	ax
	ret

endp	beep


;--------------------------------------------------------------------------------------------------
; 8-bit checksum
;--------------------------------------------------------------------------------------------------
proc	checksum	near

	mov	cx, 2000h			; Bytes in 2764 eprom

checksum_entry:
	mov	al, 0				;   zero checksum
@@loop:
	add	al, [bx]			; Add byte to checksum
	inc	bx				;   bx --> next byte
	loop	@@loop				;   loop until done
	or	al, al				; Set condition codes
	ret					;   and return

endp	checksum


;--------------------------------------------------------------------------------------------------
; Tests 1K of memory at es:0000 and increments es
;--------------------------------------------------------------------------------------------------
proc	mem_test	near

	mov	bx, 0400h			; Load bytes to test
	mov	al, 55h

ifndef	NO_MEM_CHECK
ifndef	FAST_MEM_CHECK
@@pattern_1:
	xor	di, di				; Pattern #1 - 55h bytes
	mov	cx, bx
	repz	stosb				; Fill memory,	pattern #1
	xor	di, di
	mov	cx, bx
	repz	scasb				; Scan memory for not pattern #1
	jcxz	@@pattern_2
	stc					; Flunked
	ret

@@pattern_2:
	xor	di, di				; Pattern #2 - AAh bytes
	mov	cx, bx
	not	al
	repz	stosb				; Fill memory,	pattern #2
	xor	di, di
	mov	cx, bx
	repz	scasb				; Scan memory for not pattern #2
	jcxz	@@pattern_3
	stc					; Flunked
	ret
endif

@@pattern_3:
	xor	di, di				; Pattern #3 - FFh bytes
	mov	cx, bx
	xor	al, al
	not	al
	repz	stosb				; Fill memory,	pattern #3
	xor	di, di
	mov	cx, bx
	repz	scasb				; Scan memory for not pattern #3
	jcxz	@@pattern_4
	stc					; Flunked
	ret
endif

@@pattern_4:
	xor	di, di				; Pattern #4 - 00h bytes
	mov	cx, bx
	xor	al, al
	repz	stosb				; Fill memory,pattern #4

ifndef	NO_MEM_CHECK
	xor	di, di
	mov	cx, bx
	repz	scasb				; Scan memory for not pattern #4
	jcxz	@@done
	stc					; Flunked
	ret
endif

@@done:
	mov	ax, es
	add	ax, 40h 			; Add 40h to segment number
	mov	es, ax
	ret					; Passed

endp	mem_test


;---------------------------------------------------------------------------------------------------
; 8x8 Graphics Character Set (chars 0-127)
;---------------------------------------------------------------------------------------------------
	entry	0FA6Eh				; IBM graphics character set entry

gfx_chars	db	000h, 000h, 000h, 000h, 000h, 000h, 000h, 000h		;   0  nul
		db	07Eh, 081h, 0A5h, 081h, 0BDh, 099h, 081h, 07Eh		;   1  soh
		db	07Eh, 0FFh, 0DBh, 0FFh, 0C3h, 0E7h, 0FFh, 07Eh		;   2  stx
		db	06Ch, 0FEh, 0FEh, 0FEh, 07Ch, 038h, 010h, 000h		;   3  etx
		db	010h, 038h, 07Ch, 0FEh,	07Ch, 038h, 010h, 000h		;   4  eot
		db	038h, 07Ch, 038h, 0FEh,	0FEh, 07Ch, 038h, 07Ch		;   5  enq
		db	010h, 010h, 038h, 07Ch,	0FEh, 07Ch, 038h, 07Ch		;   6  ack
		db	000h, 000h, 018h, 03Ch,	03Ch, 018h, 000h, 000h		;   7  bel
		db	0FFh, 0FFh, 0E7h, 0C3h, 0C3h, 0E7h, 0FFh, 0FFh		;   8  bs
		db	000h, 03Ch, 066h, 042h, 042h, 066h, 03Ch, 000h		;   9  ht
		db	0FFh, 0C3h, 099h, 0BDh, 0BDh, 099h, 0C3h, 0FFh		;  10  lf
		db	00Fh, 007h, 00Fh, 07Dh, 0CCh, 0CCh, 0CCh, 078h		;  11  vt
		db	03Ch, 066h, 066h, 066h, 03Ch, 018h, 07Eh, 018h		;  12  ff
		db	03Fh, 033h, 03Fh, 030h, 030h, 070h, 0F0h, 0E0h		;  13  cr
		db	07Fh, 063h, 07Fh, 063h, 063h, 067h, 0E6h, 0C0h		;  14  so
		db	099h, 05Ah, 03Ch, 0E7h, 0E7h, 03Ch, 05Ah, 099h		;  15  si
		db	080h, 0E0h, 0F8h, 0FEh, 0F8h, 0E0h, 080h, 000h		;  16  dle
		db	002h, 00Eh, 03Eh, 0FEh,	03Eh, 00Eh, 002h, 000h		;  17  dc1
		db	018h, 03Ch, 07Eh, 018h, 018h, 07Eh, 03Ch, 018h		;  18  dc2
		db	066h, 066h, 066h, 066h,	066h, 000h, 066h, 000h		;  19  dc3
		db	07Fh, 0DBh, 0DBh, 07Bh,	01Bh, 01Bh, 01Bh, 000h		;  20  dc4
		db	03Eh, 063h, 038h, 06Ch,	06Ch, 038h, 0CCh, 078h		;  21  nak
		db	000h, 000h, 000h, 000h,	07Eh, 07Eh, 07Eh, 000h		;  22  syn
		db	018h, 03Ch, 07Eh, 018h, 07Eh, 03Ch, 018h, 0FFh		;  23  etb
		db	018h, 03Ch, 07Eh, 018h, 018h, 018h, 018h, 000h		;  24  can
		db	018h, 018h, 018h, 018h, 07Eh, 03Ch, 018h, 000h		;  25  em
		db	000h, 018h, 00Ch, 0FEh, 00Ch, 018h, 000h, 000h		;  26  sub
		db	000h, 030h, 060h, 0FEh,	060h, 030h, 000h, 000h		;  27  esc
		db	000h, 000h, 0C0h, 0C0h,	0C0h, 0FEh, 000h, 000h		;  28  fs
		db	000h, 024h, 066h, 0FFh,	066h, 024h, 000h, 000h		;  29  gs
		db	000h, 018h, 03Ch, 07Eh,	0FFh, 0FFh, 000h, 000h		;  30  rs
		db	000h, 0FFh, 0FFh, 07Eh, 03Ch, 018h, 000h, 000h		;  31  us
		db	000h, 000h, 000h, 000h, 000h, 000h, 000h, 000h		;  32  space
		db	030h, 078h, 078h, 030h,	030h, 000h, 030h, 000h		;  33  !
		db	06Ch, 06Ch, 06Ch, 000h,	000h, 000h, 000h, 000h		;  34  "
		db	06Ch, 06Ch, 0FEh, 06Ch,	0FEh, 06Ch, 06Ch, 000h		;  35  #
		db	030h, 07Ch, 0C0h, 078h, 00Ch, 0F8h, 030h, 000h		;  36  $
		db	000h, 0C6h, 0CCh, 018h, 030h, 066h, 0C6h, 000h		;  37  %
		db	038h, 06Ch, 038h, 076h,	0DCh, 0CCh, 076h, 000h		;  38  &
		db	060h, 060h, 0C0h, 000h,	000h, 000h, 000h, 000h		;  39  '
		db	018h, 030h, 060h, 060h,	060h, 030h, 018h, 000h		;  40  (
		db	060h, 030h, 018h, 018h,	018h, 030h, 060h, 000h		;  41  )
		db	000h, 066h, 03Ch, 0FFh,	03Ch, 066h, 000h, 000h		;  42  *
		db	000h, 030h, 030h, 0FCh,	030h, 030h, 000h, 000h		;  43  +
		db	000h, 000h, 000h, 000h,	000h, 030h, 030h, 060h		;  44  ,
		db	000h, 000h, 000h, 0FCh,	000h, 000h, 000h, 000h		;  45  -
		db	000h, 000h, 000h, 000h,	000h, 030h, 030h, 000h		;  46  .
		db	006h, 00Ch, 018h, 030h,	060h, 0C0h, 080h, 000h		;  47  /
		db	07Ch, 0C6h, 0CEh, 0DEh,	0F6h, 0E6h, 07Ch, 000h		;  48  0
		db	030h, 070h, 030h, 030h,	030h, 030h, 0FCh, 000h		;  49  1
		db	078h, 0CCh, 00Ch, 038h,	060h, 0CCh, 0FCh, 000h		;  50  2
		db	078h, 0CCh, 00Ch, 038h,	00Ch, 0CCh, 078h, 000h		;  51  3
		db	01Ch, 03Ch, 06Ch, 0CCh,	0FEh, 00Ch, 01Eh, 000h		;  52  4
		db	0FCh, 0C0h, 0F8h, 00Ch,	00Ch, 0CCh, 078h, 000h		;  53  5
		db	038h, 060h, 0C0h, 0F8h, 0CCh, 0CCh, 078h, 000h		;  54  6
		db	0FCh, 0CCh, 00Ch, 018h,	030h, 030h, 030h, 000h		;  55  7
		db	078h, 0CCh, 0CCh, 078h,	0CCh, 0CCh, 078h, 000h		;  56  8
		db	078h, 0CCh, 0CCh, 07Ch,	00Ch, 018h, 070h, 000h		;  57  9
		db	000h, 030h, 030h, 000h,	000h, 030h, 030h, 000h		;  58  :
		db	000h, 030h, 030h, 000h,	000h, 030h, 030h, 060h		;  59  ;
		db	018h, 030h, 060h, 0C0h,	060h, 030h, 018h, 000h		;  60  <
		db	000h, 000h, 0FCh, 000h,	000h, 0FCh, 000h, 000h		;  61  =
		db	060h, 030h, 018h, 00Ch, 018h, 030h, 060h, 000h		;  62  >
		db	078h, 0CCh, 00Ch, 018h,	030h, 000h, 030h, 000h		;  63  ?
		db	07Ch, 0C6h, 0DEh, 0DEh,	0DEh, 0C0h, 078h, 000h		;  64  @
		db	030h, 078h, 0CCh, 0CCh, 0FCh, 0CCh, 0CCh, 000h		;  65  A
		db	0FCh, 066h, 066h, 07Ch, 066h, 066h, 0FCh, 000h		;  66  B
		db	03Ch, 066h, 0C0h, 0C0h, 0C0h, 066h, 03Ch, 000h		;  67  C
		db	0F8h, 06Ch, 066h, 066h, 066h, 06Ch, 0F8h, 000h		;  68  D
		db	0FEh, 062h, 068h, 078h,	068h, 062h, 0FEh, 000h		;  69  E
		db	0FEh, 062h, 068h, 078h,	068h, 060h, 0F0h, 000h		;  70  F
		db	03Ch, 066h, 0C0h, 0C0h, 0CEh, 066h, 03Eh, 000h		;  71  G
		db	0CCh, 0CCh, 0CCh, 0FCh,	0CCh, 0CCh, 0CCh, 000h		;  72  H
		db	078h, 030h, 030h, 030h,	030h, 030h, 078h, 000h		;  73  I
		db	01Eh, 00Ch, 00Ch, 00Ch,	0CCh, 0CCh, 078h, 000h		;  74  J
		db	0E6h, 066h, 06Ch, 078h,	06Ch, 066h, 0E6h, 000h		;  75  K
		db	0F0h, 060h, 060h, 060h,	062h, 066h, 0FEh, 000h		;  76  L
		db	0C6h, 0EEh, 0FEh, 0FEh,	0D6h, 0C6h, 0C6h, 000h		;  77  M
		db	0C6h, 0E6h, 0F6h, 0DEh,	0CEh, 0C6h, 0C6h, 000h		;  78  N
		db	038h, 06Ch, 0C6h, 0C6h,	0C6h, 06Ch, 038h, 000h		;  79  O
		db	0FCh, 066h, 066h, 07Ch,	060h, 060h, 0F0h, 000h		;  80  P
		db	078h, 0CCh, 0CCh, 0CCh,	0DCh, 078h, 01Ch, 000h		;  81  Q
		db	0FCh, 066h, 066h, 07Ch,	06Ch, 066h, 0E6h, 000h		;  82  R
		db	078h, 0CCh, 0E0h, 070h,	01Ch, 0CCh, 078h, 000h		;  83  S
		db	0FCh, 0B4h, 030h, 030h,	030h, 030h, 078h, 000h		;  84  T
		db	0CCh, 0CCh, 0CCh, 0CCh,	0CCh, 0CCh, 0FCh, 000h		;  85  U
		db	0CCh, 0CCh, 0CCh, 0CCh,	0CCH, 078h, 030h, 000h		;  86  V
		db	0C6h, 0C6h, 0C6h, 0D6h,	0FEh, 0EEh, 0C6h, 000h		;  87  W
		db	0C6h, 0C6h, 06Ch, 038h,	038h, 06Ch, 0C6h, 000h		;  88  X
		db	0CCh, 0CCh, 0CCh, 078h,	030h, 030h, 078h, 000h		;  89  Y
		db	0FEh, 0C6h, 08Ch, 018h,	032h, 066h, 0FEh, 000h		;  90  Z
		db	078h, 060h, 060h, 060h,	060h, 060h, 078h, 000h		;  91  [
		db	0C0h, 060h, 030h, 018h,	00Ch, 006h, 002h, 000h		;  92  backslash
		db	078h, 018h, 018h, 018h,	018h, 018h, 078h, 000h		;  93  ]
		db	010h, 038h, 06Ch, 0C6h,	000h, 000h, 000h, 000h		;  94  ^
		db	000h, 000h, 000h, 000h,	000h, 000h, 000h, 0FFh		;  95  _
		db	030h, 030h, 018h, 000h,	000h, 000h, 000h, 000h		;  96  `
		db	000h, 000h, 078h, 00Ch,	07Ch, 0CCh, 076h, 000h		;  97  a
		db	0E0h, 060h, 060h, 07Ch,	066h, 066h, 0DCh, 000h		;  98  b
		db	000h, 000h, 078h, 0CCh,	0C0h, 0CCh, 078h, 000h		;  99  c
		db	01Ch, 00Ch, 00Ch, 07Ch,	0CCh, 0CCh, 076h, 000h		; 100  d
		db	000h, 000h, 078h, 0CCh,	0FCh, 0C0h, 078h, 000h		; 101  e
		db	038h, 06Ch, 060h, 0F0h,	060h, 060h, 0F0h, 000h		; 102  f
		db	000h, 000h, 076h, 0CCh,	0CCh, 07Ch, 00Ch, 0F8h		; 103  g
		db	0E0h, 060h, 06Ch, 076h,	066h, 066h, 0E6h, 000h		; 104  h
		db	030h, 000h, 070h, 030h,	030h, 030h, 078h, 000h		; 105  i
		db	00Ch, 000h, 00Ch, 00Ch,	00Ch, 0CCh, 0CCh, 078h		; 106  j
		db	0E0h, 060h, 066h, 06Ch,	078h, 06Ch, 0E6h, 000h		; 107  k
		db	070h, 030h, 030h, 030h,	030h, 030h, 078h, 000h		; 108  l
		db	000h, 000h, 0CCh, 0FEh,	0FEh, 0D6h, 0C6h, 000h		; 109  m
		db	000h, 000h, 0F8h, 0CCh,	0CCh, 0CCh, 0CCh, 000h		; 110  n
		db	000h, 000h, 078h, 0CCh,	0CCh, 0CCh, 078h, 000h		; 111  o
		db	000h, 000h, 0DCh, 066h,	066h, 07Ch, 060h, 0F0h		; 112  p
		db	000h, 000h, 076h, 0CCh,	0CCh, 07Ch, 00Ch, 01Eh		; 113  q
		db	000h, 000h, 0DCh, 076h,	066h, 060h, 0F0h, 000h		; 114  r
		db	000h, 000h, 07Ch, 0C0h,	078h, 00Ch, 0F8h, 000h		; 115  s
		db	010h, 030h, 07Ch, 030h,	030h, 034h, 018h, 000h		; 116  t
		db	000h, 000h, 0CCh, 0CCh,	0CCh, 0CCh, 076h, 000h		; 117  u
		db	000h, 000h, 0CCh, 0CCh,	0CCh, 078h, 030h, 000h		; 118  v
		db	000h, 000h, 0C6h, 0D6h, 0FEh, 0FEh, 06Ch, 000h		; 119  w
		db	000h, 000h, 0C6h, 06Ch,	038h, 06Ch, 0C6h, 000h		; 120  x
		db	000h, 000h, 0CCh, 0CCh,	0CCh, 07Ch, 00Ch, 0F8h		; 121  y
		db	000h, 000h, 0FCh, 098h,	030h, 064h, 0FCh, 000h		; 122  z
		db	01Ch, 030h, 030h, 0E0h,	030h, 030h, 01Ch, 000h		; 123  {
		db	018h, 018h, 018h, 000h,	018h, 018h, 018h, 000h		; 124  |
		db	0E0h, 030h, 030h, 01Ch,	030h, 030h, 0E0h, 000h		; 125  }
		db	076h, 0DCh, 000h, 000h,	000h, 000h, 000h, 000h		; 126  ~
		db	000h, 010h, 038h, 06Ch,	0C6h, 0C6h, 0FEh, 000h		; 127  del


;---------------------------------------------------------------------------------------------------
; Interrupt 1Ah - Time Of Day Clock
;---------------------------------------------------------------------------------------------------
	entry	0FE6Eh				; IBM entry, time_of_day clock
proc	int_1A	far

	sti					; User time_of_day BIOS service
	push	ds
	push	ax
	mov	ax, 40h
	mov	ds, ax
	pop	ax				; Get request type
	cli					;   pause clock
	or	ah, ah
	jz	@@read				; Read time, ah=0
	dec	ah
	jnz	@@end				;   invalid request

@@set:
	mov	[ds:6Ch], dx			; Set time, ah=1
	mov	[ds:6Eh], cx			;   set time high
	mov	[byte ds:70h], 0		;   not a new day
	jmp	short @@end

@@read:
	mov	cx, [ds:6Eh]			; Read low order time
	mov	dx, [ds:6Ch]			;   high order time
	call	@@reset				; Read resets overflow

@@end:	sti					; Resume clock
	pop	ds
	iret

@@reset:
	mov	al, [ds:70h]			; Zero the overflow and return
	xor	[ds:70h], al			;   previous status in flags
	retn

endp	int_1A


;---------------------------------------------------------------------------------------------------
; Interrupt 8h - Hardware Clock
;---------------------------------------------------------------------------------------------------
	entry	0FEA5h				; IBM entry, hardware clock
proc	int_8	far

	sti					; Routine services clock tick
	push	ds
	push	dx
	push	ax
	mov	ax, 40h
	mov	ds, ax
	dec	[byte ds:40h]			; Decrement motor count
	jnz	@@increment			;   not time to shut off
	and	[byte ds:3Fh], 11110000b	; Else show motor off
	mov	al, 0Ch 			;   send motor off
	mov	dx, 3F2h			;   to the floppy
	out	dx, al				;   disk controller

@@increment:
	inc	[word ds:6Ch]			; Bump low order time of day
	jnz	@@check_midnight		;   no carry
	inc	[word ds:6Eh]			; Bump high order time of day

@@check_midnight:
	cmp	[word ds:6Eh], 18h		; Is it midnight yet?
	jnz	@@user				;   no
	cmp	[word ds:6Ch], 0B0h		; Possibly, check low order
	jnz	@@user				;   not midnight
	mov	[word ds:6Eh], 0		; Midnight, reset high order
	mov	[word ds:6Ch], 0		;   low order ticks
	mov	[byte ds:70h], 1		; Show new day since last read

@@user:
	int	1Ch				; Execute user clock service
	mov	al, 20h 			;   send end_of_interrupt
	out	20h, al 			;   to 8259 interrupt chip
	pop	ax
	pop	dx
	pop	ds
	iret

endp	int_8


;---------------------------------------------------------------------------------------------------
; Interrupt Vectors
;---------------------------------------------------------------------------------------------------
	entry	0FEF3h				; IBM entry, interrupt vector table

vectors dw	int_8				; Timer tick
	dw	int_9				; Keyboard attention
	dw	ignore_int			; Reserved
	dw	ignore_int			; Reserved for COM2 serial I/O
	dw	ignore_int			; Reserved for COM1 serial I/O
	dw	ignore_int			; Reserved for hard disk attention
	dw	int_E				; Floppy disk attention
	dw	ignore_int			; Reserved for parallel printer
	dw	int_10				; Video BIOS services
	dw	int_11				; Equipment present
	dw	int_12				; Memory present
	dw	int_13				; Disk BIOS services
	dw	int_14				; Serial communication services
	dw	int_15				; Cassette BIOS services
	dw	int_16_entry			; Keyboard BIOS services
	dw	int_17				; Parallel printer services
	dw	ignore_int			; ROM Basic (setup later)
	dw	int_19				; Bootstrap
	dw	int_1A				; Timer BIOS services
	dw	dummy_int			; Keyboard break user service
	dw	dummy_int			; System tick user service
	dw	int_1D				; Video parameter table
	dw	int_1E				; Disk parameter table
	dw	?				; Graphic character table pointer


;---------------------------------------------------------------------------------------------------
; Unexpected Interrupt
;---------------------------------------------------------------------------------------------------
	entry	0FF23h				; IBM entry, nonsense interrupt
proc	ignore_int	far

	push	ds				; Unexpected interrupts go here
	push	dx
	push	ax
	mov	ax, 40h
	mov	ds, ax
	mov	al, 0Bh 			; What IRQ caused this?
	out	20h, al
	nop
	in	al, 20h 			;   (read IRQ level)
	mov	ah, al
	or	al, al
	jnz	@@hardware
	mov	al, 0FFh			; Not hardware, say 0FFh IRQ
	jmp	short @@done

@@hardware:
	in	al, 21h 			; Clear the IRQ
	or	al, ah
	out	21h, al
	mov	al, 20h 			; Send end_of_interrupt code
	out	20h, al 			;   to 8259 interrupt chip

@@done:
	mov	[ds:6Bh], ah			; Save last nonsense interrupt
	pop	ax
	pop	dx
	pop	ds
	iret

endp	ignore_int


str_h		db	'h', 0


;---------------------------------------------------------------------------------------------------
; Dummy Interrupt
;---------------------------------------------------------------------------------------------------
	entry	0FF53h				; IBM entry, dummy interrupts
proc	dummy_int	far
;int_1B:					; Keyboard break user service
;int_1C:					; Clock    tick  user service
	iret

endp	dummy_int


;---------------------------------------------------------------------------------------------------
; Interrupt 5h - Print Screen
;---------------------------------------------------------------------------------------------------
	entry	0FF54h				; IBM entry, print screen
proc	int_5	far				; Print screen service

	sti
	push	ds
	push	ax
	push	bx
	push	cx
	push	dx
	mov	ax, 40h
	mov	ds, ax
	cmp	[byte ds:100h], 1		; Print screen in progress?
	jz	@@done				;   yes, ignore
	mov	[byte ds:100h], 1		; Flag print screen in progress
	call	print_cr_lf			;   begin new line
	mov	ah, 0Fh
	int	10h				; Get current video state
	push	ax				;   save it
	mov	ah, 3
	int	10h				; Read cursor position
	pop	ax				;   retrieve video state
	push	dx				;   save cursor position
	mov	ch, 19h 			; Do 25 rows
	mov	cl, ah				;   columns in current mode
	xor	dx, dx				; Start printing from (0, 0)

@@loop:
	mov	ah, 2				; Set cursor to position
	int	10h
	mov	ah, 8				;   and read character
	int	10h
	or	al, al				; Nulls are special case
	jnz	@@print_char
	mov	al, ' ' 			;   convert to spaces

@@print_char:
	push	dx
	xor	dx, dx
	mov	ah, dl				; Function = Print character
	int	17h
	pop	dx
	test	ah, 00100101b			; Successful print
	jz	@@next_char
	mov	[byte ds:100h], 0FFh		; No, error in Print Screen
	jmp	short @@restore_cursor

@@next_char:
	inc	dl				; Increment column count
	cmp	cl, dl
	jnz	@@loop				;   in range, continue
	mov	dl, 0
	call	print_cr_lf			; Else print new line
	inc	dh				;   add another row
	cmp	dh, ch				; Done all 25 rows?
	jnz	@@loop				;   no, continue
	mov	[byte ds:100h], 0		; Show done Print Screen OK

@@restore_cursor:
	pop	dx				; Get saved cursor position
	mov	ah, 2
	int	10h				;   restore it

@@done:
	pop	dx
	pop	cx
	pop	bx
	pop	ax
	pop	ds
	iret

endp	int_5


str_timer	db	195, ' Timer', 0


;--------------------------------------------------------------------------------------------------
; Prints CR+LF on the printer
;--------------------------------------------------------------------------------------------------
	entry	0FFCBh				; IBM entry, print CR+LF
proc	print_cr_lf	near

	push	dx				; Print CR+LF, on line printer
	xor	dx, dx
	mov	ah, dl				; Function = print
	mov	al, LF				; LF
	int	17h
	mov	ah, 0
	mov	al, CR				; CR
	int	17h
	pop	dx
	ret

endp	print_cr_lf


;--------------------------------------------------------------------------------------------------
; Sets proper underline cursor shape
;--------------------------------------------------------------------------------------------------
proc	set_cursor_size	near

	mov	[word ds:60h], 0607h		; Assume color cursor (line 6-7)
	cmp	[byte ds:49h], 7		; Mono video?
	jne	@@done				; Nope, done
	mov	[word ds:60h], 0B0Ch		; Otherwise use mono cursor (line B-C)
@@done:
	ret

endp	set_cursor_size


;--------------------------------------------------------------------------------------------------
; Power-On Entry Point
;--------------------------------------------------------------------------------------------------
	entry	0FFF0h				; Hardware power reset entry
proc	power	far				;   CPU begins here on power up

	jmpf	0F000h, cold_boot

endp	power


;--------------------------------------------------------------------------------------------------
; BIOS Release Date and Signature
;--------------------------------------------------------------------------------------------------
	entry	0FFF5h
	db	"05/02/12"			; Release date (MM/DD/YY)
						;   originally 08/23/87
	entry	0FFFEh
ifdef	IBM_PC
	db	0FFh				; Computer type (PC)
else
	db	0FEh				; Computer type (XT)
endif
;	db	0				; Checksum byte (8K ROM must sum to 0 mod 256)

ends	code

end
