The program seems to be running, and it looks like it is returning control to DOS. I can run it as many times as I want, the only problem is when I try to run anything else. My computer seems to hang (for some commands, such as dir, it just waits a long time, then finally shows me the contents of the current directory, but then a message is output on the screen: Cannot read from drive C).
;*************************************************************
;ISRSETUP.ASM - A program setting up an interrupt servive routine
; as a Teminate-and-Stay-Resident (TSR) Program, which
; can be called using Interrupt Request 72h
;*************************************************************
.MODEL small
.STACK 200h
.DATA
MASTR0 equ 20h
MASTR1 equ 21h
SLAVE0 equ 0A0h
SLAVE1 equ 0A1h
.CODE
main:
jmp start
ToBeExec Proc Far
Pushf
Push dx ;places (pushes) content of register ax onto stack
push ax ;places (pushes) content of register dx onto stack
push bx
push cx
sti
mov cx,2000 ;1st beep tone frequency
;call beep ;go sound the beep
;beep:
mov al,10110110b ;load control word
out 43h,al ;send it
mov ax,cx ;tone frequency into AX
out 42h,al ;send LSB
mov al,ah ;move MSB to AL
out 42h,al ;send it
in al,61h ;get port 61 state
or al,00000011b ;turn on speaker
out 61h,al ;speaker on now
mov bx, 600
pause1:
mov cx, 65535
pause2:
dec cx
jne pause2
dec bx
jne pause1
in al,61h
and al,11111100b
out 61h,al
;end_beep:
mov cx,2500 ;2nd beep tone frequencybeep1:
; call beep ;go sound the beep
;beep:
mov al,10110110b ;load control word
out 43h,al ;send it
mov ax,cx ;tone frequency into AX
out 42h,al ;send LSB
mov al,ah ;move MSB to AL
out 42h,al ;send it
in al,61h ;get port 61 state
or al,00000011b ;turn on speaker
out 61h,al ;speaker on now
mov bx, 600
pause3:
mov cx, 65535
pause4:
dec cx
jne pause4
dec bx
jne pause3
in al,61h
and al,11111100b
out 61h,al
;end_beep:
;jmp end_beep ;we're done
pop cx
pop bx
pop ax ;retrieves (pops) content of register ax from stack
pop dx ;retrieves (pops) content of register dx from stack
popf
IRET
ToBeExec Endp
start:
init_intctrl:
mov al,11h
out MASTR0,al
mov al,8
out MASTR1,al
mov al,4
out MASTR1,al
mov al,1
out MASTR1,al
mov al,11h
out SLAVE0,al
mov al,70h
out SLAVE1,al
mov al,2
out SLAVE1,al
mov al,1
out SLAVE1,al
;Install the new interrupt vector 72h
mov ax, cs ; get the code segment
mov ds, ax
mov dx, offset ToBeExec
mov ah, 25h ; sets the interrupt vector
; DS:DX holds the address of the new interrupt procedure
mov al, 72h ; defines the interrupt
int 21h
mov dx,00a0h ; this number indicates how many "paragraphs"
; of 16 bytes each will be reserved in memory
; for the TSR program
mov ax, 3100h ; Program Terminates and Stays Resident in memory
int 21h
mov ax,4c00h
int 21h
END main
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