_SMALLTALK AND EMBEDDED SYSTEMS_
by John Duimovich and Mike Milinkovich

Example 1

(a)


    checkSum
        "Answer a twos complement checksum of the receiver."

        <primitive: checkSum>
        ^ self primitiveFailed


(b)


    #include "userprim.h"
    DEFINE_USER_PRIMITIVE( checkSum )
    {
        char *buffer;
        unsigned int size;
        unsigned short chkSum;
        char *V_objectByteAddress();

        buffer = V_objectByteAddress(PARAM(1));
        size = V_objectSize (PARAM (1));
        for (i=0;i<size;i++) {
                chkSum += *buffer++;
        }
        SUCCEED (TO_SmallInteger(chkSum));
     }




Examplå 2

(a)


        while {1) {
            wait_for_data();
            if (enough_data) V_interruptVM (20);
        }


(b)

      Process 
          configureInterrupt: 20 
          withMessage: 
              (DirectedMessage
                  selector: #enoughDataHasArrived
                  arguments: #()
                  receiver: dataHandler).


(c)

    enoughDataHasArrived
        "Inform the process waiting for the data that the
             data has arrived."

         dataFullSemaphore signal


(d)

    [[true] whileTrue: [
        dataFullSemaphore wait.
        self processDataBuffer]] forkAt: 2




Examplå 3

    DEFINE_USER_PRIMITIVE(semaphoreSignal)
    {
        int semId; 
        IF ISNOT_SmallInteger (PARAM (1)) THEN FAIL; ENDIF
        semId = TO_long (PARAM (1));
        semGive (semId);
        SUCCEED (SELF);
     }