;INT 1H SINGLE STEPPING DEMO BY MBR_TSR
;This will be in future Versions of my Cone-Head OS

;int F9 = When Single Step mode is on Calls this int EVERY CPU instruction
;int F9 = Called by int 1 Single Step Mode DS:SI=current instruction

Org 0x0100

push cs
push cs
pop ds
pop es

mov si, Msg
call Show

mov  dx, MyInt1
mov  al, 1
call SetV

mov  dx, IntF9 ;Calls this int every CPU instruction
mov  al, 0xF9
call SetV

mov byte [cs:Int1Status], 1
int 1 ;call once to start

;Few Sample Runs...
;Some Stuff to See as CPU Instructions
mov ah, 0x0E   
mov al, 0x03
int 0x10
nop
nop
nop
mov ah, 0
mov ah, 1
mov ah, 2
mov ah, 3
mov ah, 0x4c ;WE ARE DONE!
int 0x21

SetV:
pusha
push ds
push es
cli
xor  bx, bx
mov  es, bx
mov  bl, 4
mul  bl
mov  bx, ax
mov  word [es:bx], dx
add  bx, 2
mov  word [es:bx], ds
sti
pop es
pop ds
popa
ret

MyInt1:
pop word [cs:SSOff]
pop word [cs:SSSeg]
push word [cs:SSSeg]
push word [cs:SSOff]
push bp
mov bp, sp
push ax
push ds
push cs
pop ds
mov al, byte [cs:Int1Status]
cmp al, 1
jne Not1Honey
or WORD [bp + 6], 0100h
mov al, 3
mov byte [cs:Int1Status], al
jmp NoneBaby
Not1Honey:
mov al, byte [cs:Int1Status]
cmp al, 0
jne Routine
and WORD [bp + 6], 0feffh
jmp NoneBaby
Routine:
push ds
push si
mov si, word [cs:SSOff]
mov ds, word [cs:SSSeg]
int 0xF9
pop si
pop ds
NoneBaby:
pop ds
pop ax
pop bp
iret

;Dump ds:si as hex call with cx=count
DumpHex:
push ax
push bx
push cx
push si
Dumper:
lodsb
push cx
MOV  CL,10h
MOV  AH,0
DIV  CL
ADD  AL,30h
ADD  AH,30h
CMP  AL,'9'
JBE  zCA4B
ADD  AL,7
zCA4B:
CMP  AH,'9'
JBE  zCA5B
ADD  AH,7
zCA5B:
mov  CX, AX
mov  al, CL
mov  ah, 0eh
mov  bh, 0
mov  bl, 1
int  10h
mov  al,CH
mov  ah, 0eh
mov  bh, 0
int  10h
mov  ah, 0x0e
mov  al, ' '
mov  bx, 0x000f
int  0x10
pop  cx
loop Dumper
pop  si
pop  cx
pop  bx
pop  ax
ret

;Called by Int 1h Every Instruction
;DS:SI=CS:IP
IntF9:
mov  cx, 8    ;How many Bytes to Show
call DumpHex
call PrintCRLF
iret

PrintCRLF:
mov ah, 0x0E
mov al, 0x0D
int 0x10
mov al, 0x0A
int 0x10
ret

Show:
push ax
push bx
push si
Show1:
lodsb
cmp  al, 0
je   Okay
mov  ah, 0x0E
mov  bh, 0x00
mov  bl, 0x07
int  0x10
jmp  Show1
Okay:
pop  si
pop  bx
pop  ax
ret

Msg db "Int1 Single Step Demo Dump CS:IP as Hex", 13,10, 0

Int1Status db 0         ;Int 1 Single Step 0=OFF 1=ON
SSSeg dw 0x0000
SSOff dw 0x0000

;Thats All!