; ============================================================================
;
; LT-DOS - Int 21h program
;
; ============================================================================
PSPFILES EQU 20 ; maximum number of open files in PSP
DTASIZE EQU 128 ; DTA (Data Transfer Address) size
; ------------- Program Segment Prefix, PSP
struc PSP
PSP_Int20: resb 2 ; 0: Int 20h instruction for CALL 0
PSP_FreeMem: resw 1 ; 2: segment of first free memory
resb 1 ; 4: ...reserved (unused)
PSP_Call5: resb 5 ; 5: CP/M Call 5 service
; (far call 0000:00c0h instruction)
PSP_Int22: resd 1 ; 0Ah: Int 22h address (termination)
PSP_Int23: resd 1 ; 0Eh: Int 23h address (Ctrl+C)
PSP_Int24: resd 1 ; 12h: Int 24h address (error)
PSP_Parent: resw 1 ; 16h: segment of parent PSP
PSP_File: resb PSPFILES ; 18h: JFT (Job File Table),0ffh=closed
PSP_Env: resw 1 ; 2Ch: segment of environment
PSP_Stack: resd 1 ; 2Eh: last SS:SP on entry to Int 21h
PSP_Files: resw 1 ; 32h: number of entries in JFT (20)
PSP_FileTab: resd 1 ; 34h: pointer to JFT (PSP:0018h)
PSP_PrevPSP: resd 1 ; 38h: pointer to previous PSP (-1)
resb 20 ; 3Ch: ...reserved (unused)
PSP_Serv: resb 3 ; 50h: service request (Int 21h + retf)
resb 9 ; 53h: ...reserved (unused)
PSP_FCB1: resb UFCB_SIZE ; 5Ch: first default unopen FCB
; (filled from first argument)
PSP_FCB2: resb UFCB_SIZE ; 6Ch: second default unopen FCB
; (filled from second argument)
resb 4 ; 7Ch: ...reserved (unused)
PSP_DTA: resb DTASIZE ; 80h: commandline and default DTA
; contains byte with length of
; commandline and text of commandline
endstruc
PSP_SIZE EQU PSP_size ; 100h = 256 bytes
; ------------- Program environment
; - (x) first environment variable, ASCIIZ string in form "var=value"
; - (x) second environment variable, ASCIIZ string in form "var=value"
; ...
; - (x) last environment variable, ASCIIZ string in form "var=value"
; - (1) terminating byte 0
; - (2) number of strings following environment (normally 1)
; - (x) ASCIIZ full pathname of program owning this environment
; ... other strings
; ----------------------------------------------------------------------------
; Int 21h, function 50h - set segment of new current PSP
; ----------------------------------------------------------------------------
; INT21 INPUT: AH = 50h (function code)
; BX = segment of new current PSP
; ----------------------------------------------------------------------------
; NOTES: - does not use internal stack (may be called at any time)
; ----------------------------------------------------------------------------
Int2150: mov [cs:CurrentPSP],bx ; segment of new current PSP
ret
; ----------------------------------------------------------------------------
; Int 21h, function 51h - get segment of current PSP
; ----------------------------------------------------------------------------
; INT21 INPUT: AH = 51h (function code)
; INT21 OUTPUT: BX = segment of PSP for current process
; ----------------------------------------------------------------------------
; NOTES: - does not use internal stack (may be called at any time)
; ----------------------------------------------------------------------------
Int2151: mov bx,[cs:CurrentPSP] ; BX <- current PSP
call SetRegBX ; set output register BX
ret
; ----------------------------------------------------------------------------
; Data
; ----------------------------------------------------------------------------
; ------------- Current process
CurrentPSP: dw 0 ; segment of PSP for current process
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