extrn	$$main:far

cseg	segment para public 'code'





; This program is used to set the PSP address for a compiled BASIC program.

; The PSP segment is saved at 0:4F2H.



; It can also be used to limit the maximum memory available to a compiled

; BASIC program. The option '/M:nnn' is used on the command line, where

; nnn is the number of K-bytes the program is limited to. If no, /M option

; is specified, no memory limitation takes place. For example, '/M:64' would

; limit the program to 64*1024 bytes. The range for nnn is 64 to 1024.



; This routine gets control before BASIC, does its handiwork, and then

; passes control to the BASIC program. It must be linked as follows:

; LINK BASMAIN yourprog,yourprog,NUL.MAP,BASCOM



; If BASMAIN is unable to limit memory as requested, a message is displayed

; and the execution of the program is continued.



public	basmain

basmain proc far

	assume cs:cseg,ds:cseg,ss:nothing,es:nothing



	push ds 		; save ds

	xor ax,ax

	mov ds,ax		; ds=0

	mov si,4f2h		; dos communications area

	mov ax,es		; get psp seg

	mov [si],ax		; save psp in dos comm area

	pop ds			; restore ds

	mov si,80h		; point to command line

	mov ch,0

	mov cl,[si]		; get length of command line

	jcxz p025		; it's zero



p010:	inc si

	mov al,[si]		; get char from command line

	cmp al,'/'              ; is it a slash?

	jnz p020		; no

	mov ax,[si 1]		; get next 2 chars

	cmp ax,':M'             ; is it M: ?

	jz p030 		; yes

	cmp ax,':m'             ; is it m: ?

	jz p030 		; yes



p020:	loop p010		; check next char

p025:	jmp p080		; no /m: or /M: found



p030:				; found /m: or /M:

	add si,3		; point to first number

	mov ax,0

	mov bx,0

	mov cx,10

p040:	mov bl,[si]		; get character

	cmp bl,'0'              ; out of range?

	jb p050 		; yes

	cmp bl,'9'              ; out of range?

	ja p050 		; yes

	sub bl,'0'              ; convert to binary

	mul cx			; multiply ax by 10

	add ax,bx		; add new digit

	inc si			; point to next char

	jmp p040		; continue



p050:				; got value in ax

	cmp ax,64		; less than 64K?

	jb p060 		; yes - print msg

	cmp ax,1024		; greater than 1024K?

	ja p060 		; yes - print msg

	mov cl,6

	sal ax,cl		; convert from KB to paragraphs (*64)

	mov bx,es		; get psp

	add bx,ax		; new top of memory

	mov si,2		; point to top of memory in psp

	mov ax,[si]		; get current top of memory

	cmp ax,bx		; is new setting larger?

	jae p055		; no

	mov dx,offset msg2	; yes - print msg

	jmp p065



p055:	mov [si],bx		; save new top of memory

	jmp p080



p060:	mov dx,offset msg1	; print the message

p065:	add dx,100h		; fudge for the psp

	mov ah,9

	int 21h



p080:	jmp $$main		; jump to BASIC's start point



msg1	db 'Memory specification must be from 64 to 1024',7,10,13,'$'

msg2	db 'Unable to limit memory',7,10,13,'$'



basmain endp

cseg	ends

end	basmain 		; must be a main program!