Category : Assembly Language Source Code
Archive   : TASMSWAN.ZIP
Filename : SINGLE.ASM

%TITLE "Single-step (trap) demo"

IDEAL
DOSSEG
MODEL small
STACK 256


cr EQU 13
lf EQU 10
Trapping EQU 0
TurnOnTrap EQU 1
TurnOffTrap EQU 2


DATASEG

exitCode db 0
spaces db ' ',0
offMsg db cr,lf,'Single-step trap is off',cr,lf,0
onMsg db cr,lf,'Single-step trap is on',cr,lf,0
pauseMsg db cr,lf,'Press any key to continue ...',0
countMsg db cr,lf,lf,'Count = 50!',cr,lf,0
trapSwitch db 0
string db 40 DUP (?)
count dw ?
trapSeg dw ?
trapOfs dw ?


CODESEG

;--------- from STRIO.obj, BINASC.obj, KEYBOARD.obj
EXTRN StrWrite:proc, NewLine:proc, BinToAscDec:proc
EXTRN BinToAscHex:proc, GetCh:proc

Start:
mov ax,@data
mov ds,ax
mov es,ax
mov ax,3501h
mov [trapSeg],es
mov [trapOfs],bx
push ds
mov ax,2501h
push cs
pop ds
mov dx, offset Stepper
int 21h
pop ds
mov di, offset offMsg
call Counter
mov di, offset onMsg
mov [trapSwitch], TurnOnTrap
int 1
call Counter
mov [trapSwitch],TurnOffTrap

mov di, offset offMsg
call Counter
Exit:
push ds
mov ax,2501h
mov ds,[trapSeg]
mov dx,[trapOfs]
int 21h
pop ds
mov ah,04Ch
mov al,[exitCode]
int 21h

PROC Counter
call StrWrite
call Pause
mov [count],0
@@10:
inc [count]
mov ax,[count]
mov cx,4
mov di, offset string
call BinToAscDec
call StrWrite
mov di, offset spaces
call StrWrite
cmp [count],100
jb @@10
ret
ENDP Counter

PROC Pause
mov di, offset pauseMsg
call StrWrite
call GetCh
call NewLine
ret
ENDP Pause

%NEWPAGE
;------------------------------------------------------------------------
; Stepper - Single-step trap ISR
;------------------------------------------------------------------------
; Input: [trapSwitch] = TurnOnTrap -> Single-step mode enabled
; [trapSwitch] = TurnOffTrap -> Single-step mode disabled
; [trapSwitch] = ??? -> NO action
; Output: none
; Registers: none
;------------------------------------------------------------------------
PROC Stepper
sti
push bp
mov bp,sp
push ax
push bx
push cx
push dx
push di
push si
push ds
push es
mov ax,@data
mov ds,ax
mov es,ax
cmp [trapSwitch], TurnOnTrap
jne @@10
or [word bp + 6], 0100h
mov [trapSwitch], Trapping
jmp @@99
@@10:
cmp [trapSwitch], TurnOffTrap
jne @@20
and [word bp + 6], 0FEFFh
jmp @@99
@@20:
cmp [count], 50
jne @@99
mov di,offset countMsg
call StrWrite
call Pause
inc [count]
call NewLine
@@99:
pop es
pop ds
pop si
pop di
pop dx
pop cx
pop bx
pop ax
pop bp
iret
ENDP Stepper

END Start