Question: What do the environment variables do ?

Answer:

The D_DIR environment variable is used to tell the Debugger which directory contains the files emuinit.cmd, init.clr, c4x510ws.out, are init.pdm.

The D_SRC environment variable is used to tell the Debugger which directories contain source files (*.asm and *.c files).

The D_OPTIONS environment variable is used to tell the Debugger to always use specific command line options.