CODE_SEG SEGMENT
ASSUME CS:CODE_SEG,DS:code_seg

ORG 100H

START:
JMP BEGIN
;================================== data ====================================
int_2Fh_vector DD ?
old_09h DD ?

flag        DB  0
; window's coords
high_Y      DB  01
left_X      DB  01
low_Y       DB  15
right_X     DB  30
;
page_num    DB  0
;message's coords in window
coord_Y     DB  4
coord_X     DB  15

buffer      DB  ?
tail        DW 0
count       DB 0
;=============================================================================
new_09h proc far
    push AX
    push ES

    mov AX,40h
    mov ES,AX
    mov AX,ES:[1Ch]
    mov CS:tail,AX

    pop ES
    pop AX

    pushf
    call CS:old_09h

    push AX
    push BX
    push ES

    mov AX,40h
    mov ES,AX
    mov BX,CS:tail
    cmp BX,ES:[1Ch]
    je exit1
    jmp cont
exit1:
    pop ES
    pop BX
    pop AX
    iret
cont:
    pushf
    push    AX
    in      AL,60h    ; enter scan-code
    cmp     AL,58h      ; scan-code <F12>
    je      hotkey      ; Yes
    inc CS:count
    pop     AX    ; No. Restore AX
    popf
    jmp     dword ptr CS:[old_09h]
hotkey:
    sti
    in      AL,61h      ; Enter B port's content
    or      AL,80h      ; Set elder bit
    out     61h,AL      ; return to content to B port.
    and     AL,7Fh      ; Enable keyboard,
    out     61h,AL      ; Reset older bit from B port .
;
;-------------------- Window output by BIOS ---------------------------
;
    ;save used registers
            push    BX
            push    CX
            push    DX
            push    DS
    ;set our register to ds
            push    CS  ;
            pop     DS  ;
;----------------------------------------------------------------------------
        mov     AX, 0600h      ; Set window
        mov     BH, 70h        ; attribute Black on write
        ;window's coordinates
        mov     CH, high_Y
        mov     CL, left_X
        mov     DH, low_Y
        mov     DL, right_X
        int 10h
; ------------------------ Set cursors's position -----------------------------
        mov     AH,02h       ; Set position func
        mov     BH,page_num  ; Video
        mov     DH,coord_Y   ; string
        mov     DL,coord_X   ; row
        int 10h

    mov ah, 2
    mov dl, count
    int 21h
;return cursor
;        mov     AH,02h          ; Set position func
;        mov     BH,0;
;        mov     DH,24  ; string
;        mov     DL,12  ; row
;        int 10h

            pop     DS  ; Reset registers
            pop     DX
            pop     CX
            pop     BX
;---------------------------------------------------------------------------
    cli
    ;end of interrupt
    mov     AL, 20h
    out     20h,AL
;
    pop     AX
    popf

;============================
exit:
pop ES
pop BX
pop AX
iret
new_09h endp
;=============================================================================
;
;=============================================================================
int_2Fh proc far
    cmp     AH,0C7h         ; Is it our num?
    jne     Pass_2Fh        ; go exit
    cmp     AL,00h          ; Already installed?
    je      inst            ;
    cmp     AL,01h          ; Unload?
    je      unins           ; Yes, go to unload
    jmp     Pass_2Fh        ; Unknown command
inst:
    mov     AL,0FFh         ; Already installed
    iret
Pass_2Fh:
    jmp dword PTR CS:[int_2Fh_vector]
;
; -------------- Is unload possible ? ------
unins:
    push    BX
    push    CX
    push    DX
    push    ES
;
    mov     CX,CS   ; for compairing
    mov     AX,3509h    ; check 09h
    int     21h ; Return vector in ES:BX
;
    mov     DX,ES
    cmp     CX,DX
    jne     Not_remove
;
    cmp     BX, offset CS:new_09h
    jne     Not_remove
;
    mov     AX,352Fh    ; Check vector 2Fh
    int     21h
;
    mov     DX,ES
    cmp     CX,DX
    jne     Not_remove
;
    cmp     BX, offset CS:int_2Fh
    jne     Not_remove
    ; ---------------------- Unload from memory ---------------------
;
    push    DS
;
    lds     DX, CS:old_09h
    mov     AX,2509h        ; Fill vector by old content
    int     21h
;
    lds     DX, CS:int_2Fh_vector
    mov     AX,252Fh
    int     21h
;
    pop     DS
;
    mov     ES,CS:2Ch       ; ES -> enviroment
    mov     AH, 49h         ; Free memory function
    int     21h
;
    mov     AX, CS
    mov     ES, AX          ; ES -> PSP unload programm
    mov     AH, 49h         ; Free memory function
    int     21h
;
    mov     AL,0Fh          ; Successful uninstall
    jmp     pop_ret
Not_remove:
    mov     AL,0F0h          ; Can't unload
pop_ret:
    pop     ES
    pop     DX
    pop     CX
    pop     BX
;
    iret
int_2Fh endp
;=============================================================================
begin:
mov AX,0C700h
int 2Fh
cmp AL, 0
jz not_installed
lea DX,msg
call print
int 20h
msg DB 'Already installed',13,10,'$'
not_installed:
mov AX,352Fh
int 21h
mov word ptr int_2Fh_vector,BX
mov word ptr int_2Fh_vector+2,ES
mov DX,offset int_2Fh
mov AX,252Fh
int 21h
mov AX,3509h
int 21h
mov word ptr old_09h,BX
mov word ptr old_09h+2,ES
mov DX,offset new_09h
mov AX,2509h
int 21h
;------------------------------------------------------------------------------
mov DX,offset begin
int 27h
;=============================================================================
PRINT PROC NEAR
MOV AH,09H
INT 21H
RET
PRINT ENDP
;=============================================================================
CODE_SEG ENDS
END START