Обработчик прерываний

.model small
.stack 100h
.code
.186 
start:
    jmp init
    
int09h_handler proc  far
    jmp work
    
    old_int09h dd 0
 
work:
    pusha
    push ds
    push es
 
    pushf
    mov ax, cs:trigger
    not ax
    mov trigger, ax
    cmp ax, 0
    je label12
    call dword ptr cs:old_int09h
label12:
    cld
    push 0B800h
    pop es
    push 0040h
    pop ds
    
    
    mov di, word ptr ds:001Ah
 
    cmp di, word ptr ds:001Ch
    je exit_09handler
 
    mov ax,word ptr [di]
    
exit_09handler:
    pop es
    pop ds
    popa
    iret
int09h_handler  endp
 
int21h_handler proc far
    cmp ax, 7200h
    jne default21h
    mov ah, 123
    iret
    default21h:
        jmp cs:old_int21h
    old_int21h dd 0
int21h_handler  endp    
 
init proc
    ;check if handler has already installed
    mov ah, 72h
    int 21h
    cmp ah, 123
    je installed 
    ;if not installed
    ;install 09h handler
    push cs
    pop ds 
    mov ax, 3509h                   
    int 21h
    mov word ptr old_int09h,  bx     
    mov word ptr old_int09h + 2,  es 
    mov ax, 2509h 
    mov dx, offset int09h_handler
    int 21h
    ;install 21h handler
    mov ax, 3521h                   
    int 21h
    mov word ptr old_int21h,  bx     
    mov word ptr old_int21h + 2,  es 
    mov ax, 2521h 
    mov dx, offset int21h_handler
    int 21h
    ;print message
    mov ax, @data
    mov ds, ax
    lea dx, msg_ready
    mov ah, 9
    int 21h
    ;keep code in memory
    mov dx, (init - start + 10Fh)/16
    mov ax, 3100h
    int 21h
;===================================
    ;if handler already installed
    installed:
    cmp byte ptr ds:[80h], 3
    jne print_already
    cmp byte ptr ds:[82h], '\'
    jne print_already
    cmp byte ptr ds:[83h], 'q'
    jne print_already
    ;delete handlers
    mov ax, 3509h
    int 21h
    cli
    mov dx, word ptr es:old_int09h + 2
    mov ds, dx
    mov dx, word ptr es:old_int09h
    mov ah, 25h
    int 21h
    mov al, 21h
    mov dx, word ptr es:old_int21h + 2 
    mov ds, dx
    mov dx, word ptr es:old_int21h
    int 21h 
    sti
    mov ah, 49h
    int 21h
    jmp print_deleted
;=======================
    print_already:
    mov ax, @data
    mov ds, ax
    lea dx, msg_already
    mov ah, 9h
    int 21h
    mov ax, 4C00h
    int 21h
    
    print_deleted:
    mov ax, @data
    mov ds, ax
    lea dx, msg_deleted
    mov ah, 9h
    int 21h
    mov ax, 4C00h
    int 21h
init endp   
.data
    trigger dw 1
    msg_ready db "Resident is in the memory", 24h
    msg_already db "Resident already is in the memory", 24h
    msg_deleted db "Resident deleted from memory", 24h
end start