; to assemble use the following command line:
; nasm.exe -f bin kbd.asm -o kbd.com

bits 16
org 0x100

    xor     ax, ax
    mov     es, ax

	; set our ISR
    cli
    push    word [es:9*4+2]
    push    word [es:9*4]
    mov     word [es:9*4], kbdIRQ1
    mov     [es:9*4+2],cs
    sti

    call    main

    cli
    pop     word [es:9*4]
    pop     word [es:9*4+2]
    sti

    ret

main:
    mov     ah, 9
    mov     dx, msg
    int     0x21

keylookup:

	mov 	bx, kbdbuf
	xor		cx, cx
search:
	mov 	al, [bx] ; take key status

	test 	al, al
	jnz  	found ; key was pressed

	inc     bx
	inc 	cx
	cmp 	cx, 0x32 ; search until key scan code 'M' is reached (last letter)
	jbe		search

	jmp 	keylookup

found:
	cmp		cx, 1 ; Escape was pressed
	je		finished

	; convert to corresponding ascii code using ascii table
	sub 	cx, 0x10
	mov     bx, ascii
	add		bx, cx
	mov		al, [bx]

	mov		bx, letter
	mov		[bx], al

	mov 	dx, bx
	mov 	ah, 9
	int 	0x21

	; convert to binary
	mov		al, [bx]
	mov 	bx, bincode
	add		bx, 8
convert:
	dec     bx
	mov     cl, al
	and     cl, 1
	add     cl, 0x30
	mov     [bx], cl

	shr     al, 1
	cmp     bx, bincode
	jnz     convert

	mov 	dx, bx
	mov 	ah, 9
	int 	0x21

	; reverse the binary code
reverse:
	mov		bl, [letter]
	xor		al, al
	mov		cl, 8

reverseloop:
	mov		dl, bl
	and		dl, 1
	shl		al, 1
	or		al, dl
	shr		bl, 1
	dec		cl
	jnz		reverseloop

	; save the value in letter
	mov		[letter], al

	; print the reversed binary
	mov 	bx, bincode
	add		bx, 8
convert2:
	dec     bx
	mov     cl, al
	and     cl, 1
	add     cl, 0x30
	mov     [bx], cl

	shr     al, 1
	cmp     bx, bincode
	jnz     convert2

	mov 	dx, bx
	mov 	ah, 9
	int 	0x21

	; output the key to parallel port
	mov		dx, letter
	mov 	ah, 9
	int 	0x21

jmp keylookup

finished:
    ret

kbdIRQ1:
    pusha

    ; read keyboard scan code
    in      al, 0x60

    ; bx = keyboard scan code
    xor     bh, bh
    mov     bl, al
    and     bl, 0x7F
    shr     al, 7
    xor     al, 1 ; al = 1 if pressed, 0 if released
    mov     [cs:bx+kbdbuf], al

    ; send EOI to XT keyboard and PCI master
    in      al, 0x61
    mov     ah, al
    or      al, 0x80
    out     0x61, al
    mov     al, ah
    out     0x61, al
    mov     al, 0x20
    out     0x20, al

    popa
    iret

kbdbuf:
    times   128 db 0

msg db "Press any letter on your keyboard (press esc to exit)", 13, 10, "$"
bin db "        ", 13, 10, "$"
letter db " ", 13, 10, "$"
bincode db "        ", 13, 10, "$"
ascii db "qwertyuiop    asdfghjkl     zxcvbnm", "$"