Writing to a file from a TSR (MASM16)
 

Hi,

I am having a hard time writing to a file from a TSR routine. The routine is supposed to write a line of text to a file when the F9 key is pressed. Instead it just prints the line to the screen. I am only posting the parts of the routine I having problems with. I thikn I setup the IVT table correctly.

Thanks,
Kevin

; --------------------------------------------------
; Example layout for interrupt handler.

.model tiny
.486
text segment public 'CODE'

; Note, must put start of program at 100 hex,

org 100h
start:
jmp init

; note, required to "start" just past the "org",
; so jump, not call, since we will not return.

myint proc far
pushf
call CS:oldn

push ax
push bx
push cx
push dx
push ds
push es

mov ax,cs
mov ds,ax

; Check for F9 down
cmp ax, 43h
je no_err

; Check for F9 up, file write
cmp ax, 0c3h
je filewrite

; If we see any other key, just beep
jmp err

; write the stars line to the file
filewrite:
mov ah, 40h
mov bx, es:fhand
mov cx, 82
lea dx, es:stars
int 21h
jc err

; Commit the line
mov ah, 68h
mov bx, es:fhand
int 21h
jmp no_err

As a new member, it would seem prudent to read the forum's rules/FAQ and a "How to Post...." thread, just to get in tune with this (and many similar) community(s), right? Attention to the part regarding code tags would certainly be in order.

Your problem might be that DOS is non-reentrant, and you're trying to call it from what appears to be an interrupt context. Without seeing exactly how you get those scancodes into AX, or under what conditions your TSR is invoked, I can't say for sure (since, according to the code, AX has your program's CS value).