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95 lines
2.6 KiB
NASM
95 lines
2.6 KiB
NASM
4 years ago
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extrn $$main:far
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cseg segment para public 'code'
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; It can also be used to limit the maximum memory available to a compiled
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; BASIC program. The option '/M:nnn' is used on the command line, where
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; nnn is the number of K-bytes the program is limited to. If no, /M option
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; is specified, no memory limitation takes place. For example, '/M:64' would
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; limit the program to 64*1024 bytes. The range for nnn is 64 to 1024.
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; This routine gets control before BASIC, does its handiwork, and then
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; passes control to the BASIC program. It must be linked as follows:
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; LINK BASMAIN+yourprog,yourprog,NUL.MAP,BASCOM
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; If BASMAIN is unable to limit memory as requested, a message is displayed
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; and the execution of the program is continued.
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public basmain
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basmain proc far
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assume cs:cseg,ds:cseg,ss:nothing,es:nothing
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push ds ; save ds
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xor ax,ax
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mov ds,ax ; ds=0
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mov si,4f2h ; dos communications area
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mov ax,es ; get psp seg
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mov [si],ax ; save psp in dos comm area
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pop ds ; restore ds
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mov si,80h ; point to command line
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mov ch,0
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mov cl,[si] ; get length of command line
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jcxz p025 ; it's zero
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p010: inc si
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mov al,[si] ; get char from command line
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cmp al,'/' ; is it a slash?
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jnz p020 ; no
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mov ax,[si+1] ; get next 2 chars
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cmp ax,':M' ; is it M: ?
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jz p030 ; yes
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cmp ax,':m' ; is it m: ?
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jz p030 ; yes
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p020: loop p010 ; check next char
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p025: jmp p080 ; no /m: or /M: found
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p030: ; found /m: or /M:
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add si,3 ; point to first number
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mov ax,0
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mov bx,0
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mov cx,10
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p040: mov bl,[si] ; get character
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cmp bl,'0' ; out of range?
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jb p050 ; yes
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cmp bl,'9' ; out of range?
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ja p050 ; yes
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sub bl,'0' ; convert to binary
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mul cx ; multiply ax by 10
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add ax,bx ; add new digit
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inc si ; point to next char
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jmp p040 ; continue
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p050: ; got value in ax
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cmp ax,64 ; less than 64K?
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jb p060 ; yes - print msg
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cmp ax,1024 ; greater than 1024K?
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ja p060 ; yes - print msg
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mov cl,6
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sal ax,cl ; convert from KB to paragraphs (*64)
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mov bx,es ; get psp
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add bx,ax ; new top of memory
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mov si,2 ; point to top of memory in psp
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mov ax,[si] ; get current top of memory
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cmp ax,bx ; is new setting larger?
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jae p055 ; no
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mov dx,offset msg2 ; yes - print msg
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jmp p065
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p055: mov [si],bx ; save new top of memory
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jmp p080
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p060: mov dx,offset msg1 ; print the message
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p065: add dx,100h ; fudge for the psp
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mov ah,9
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int 21h
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p080: jmp $$main ; jump to BASIC's start point
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msg1 db 'Memory specification must be from 64 to 1024',7,10,13,'$'
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msg2 db 'Unable to limit memory',7,10,13,'$'
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basmain endp
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cseg ends
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end basmain ; must be a main program!
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