So I have this book that has an example TSR written in MASM, al it doe sit look at the keyboard flags and if the user presses CTRL+ALT+DEL is if change turns off the CTRL bit. If the user pressss CTRL_ALT_Rgt Shift+DEL is will original handler.
I pretty much have it working except after it installs I can no longer type anything so I am guessing it's not calling the old handler. I am pretty sure I have the jump addresses incorrect but not sure how to get that working.
I had originally pasted int the MASM source but was concerned that it might be copyrighted so I removed it and I removed unrelated code from my version as I believe the issue is either setting the interrupt vector or the jumping to the original one. Perhaps I am not jumping correctly.
org 100h
main:
jmp setup
int9_handler:
sti ; enable hardware interupts
pushf ; save regs and flags
push es
push ax
push di
pop di
pop ax
pop es
popf
jmp [cs:old_interupt9]
old_interupt9 dw 2 dup (?)
end_isr: db 1 dup (?)
; ----------------------------------------------
; Save copy of original interrupt 9 vector, and setup
; the address of the program as the new vector, terminate
; this program and leave int9_handler procedure in memory.
setup:
mov ax, 0x3509 ; get int9 vector
int 0x21
mov word [old_interupt9], bx ; save int9 vector
mov word [old_interupt9+2], es
mov ax, 0x2509 ; set int9 vector
mov dx, int9_handler
int 0x21
mov ax, 0x3100 ; terminate and stay resident
mov dx, end_isr ; point to end of resident code
shr dx, 4 ; divide by 16
inc dx ; round forward one paragraph
int 0x21
What am I missing?
thanks,
Tyson
