pop ax ;restore registers
iret ;return to caller
new_int_9h endp
begin proc near
push es ;save psp base address
mov dx,seg msgs
mov ds,dx
mov dx,offset msg_0
mov ah,9
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int 21h
mov ax,3500h free_vector
int 21h
mov di,bx ;ES:DI ===> start of INT 0CDh ISR
mov si,offset copyright
mov ax,cs
mov ds,ax ;DS:SI ===> THIS code copyright notice
mov cx,cright_len
cld
repe cmpsb ;compare
je loaded ;if equal then already loaded
mov ax,2500h free_vector
mov dx,cs
mov ds,dx
mov dx,offset copyright
int 21h ;point free_vector INT vector to
;our copyright notice
mov ax,3509h
int 21h ;get pointer to INT 9 ISR
mov cs:old_int_9_ofs,bx
mov cs:old_int_9_seg,es ;put it IN the new INT 9 ISR
mov ax,2509h
mov dx,offset new_int_9h
push cs
pop ds
int 21h ;point INT 9 vector to our ISR
mov dx,seg msgs
mov ds,dx
mov dx,offset msg_1
mov ah,9
int 21h ;print loaded msg
pop ds ;get saved psp base address
mov es,ds:(2Ch)
mov ah,49h
int 21h ;free environment's memory
;assume no error
mov dx,offset begin ;everything up to BEGIN
add dx,10Fh ;and all the bytes needed to
mov cl,4 ;make a full paragraph ...
shr dx,cl
mov ax,3100h ;... stay resident
int 21h ;and return exit code = 0
loaded: pop ax ;get psp address out of stack
;any register will do
mov dx,seg msgs
mov ds,dx ;point DS to our data area
mov dx,offset msg_2
mov ah,9
int 21h ;print already loaded msg
mov ax,4C01h
int 21h ;terminate with exit code = 1
begin endp
nocad ends
msgs segment word 'DATA'
msg_0 db 10,13,'NOCAD: Prevent CTRL ALT DEL from restarting the '
db 'system',10,13,'Author: Antonio Quezada-Duarte',10,13,'$'
msg_1 db 10,13,'NOCAD Loaded OK.',10,13,'$'
msg_2 db 10,13,'NOCAD Already Loaded.',10,13,'$'
msgs ends
stack segment para stack 'STACK'
dw 1024 dup (?)
stack ends
end begin
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