;===============================================================================
; Virtual Piano -- a virtual and playable piano
; By SirPython of Code Review and GitHub
;
; virtual_piano.asm
;===============================================================================

%define MIDI_CONTROL_PORT 0331h
%define MIDI_DATA_PORT 0330h
%define MIDI_UART_MODE 3Fh
%define MIDI_PIANO_INSTRUMENT 93h

start:
    call setup_midi
    mov ch, 60;             default octave(0)
    mov cl, 5;              used for making sure that the user does not go too low or too high with the octaves
.loop:
    call read_character
    call process_input

    cmp bh, 0;              if bad input OR octave change goes out of range
    je .loop

    call get_pitch

    cmp bh, 2;              if shouldn't play note (was an octave switch)
    je .loop

    call play_note

    jmp .loop

;--------------------------------------------------
; Plays a note
;
; IN: AL, CH = pitch, (octave * 12) + 60
; OUT: NONE
; ERR: NONE
; REG: AL

play_note:
    add al, ch;             apply the octave
    out dx, al;             DX will already contain MIDI_DATA_PORT from the setup_midi function

    mov al, 7Fh;            note duration
    out dx, al

    ret

;--------------------------------------------------
; Based on input, returns a pitch to be played
;
; IN: AL = key code
; OUT: AL, BH, CH = pitch, 2 if no pitch to be played, (octave * 12) + 60
; ERR: NONE
; REG: preserved

get_pitch:
    cmp al, 'a'
    je .a
    cmp al, 's'
    je .s
    cmp al, 'd'
    je .d
    cmp al, 'f'
    je .f
    cmp al, 'j'
    je .j
    cmp al, 'k'
    je .k
    cmp al, 'l'
    je .l
    cmp al, ';'
    je .sc

    cmp al, 'w'
    je .w
    cmp al, 'e'
    je .e
    cmp al, 'r'
    je .r
    cmp al, 't'
    je .t
    cmp al, 'i'
    je .i
    cmp al, 'o'
    je .o
    cmp al, 'p'
    je .p

    cmp al, 'z'
    je .z
    cmp al, 'x'
    je .x

.a: mov al, 0
    jmp .end
.s: mov al, 2
    jmp .end
.d: mov al, 4
    jmp .end
.f: mov al, 5
    jmp .end
.j: mov al, 7
    jmp .end
.k: mov al, 9
    jmp .end
.l: mov al, 11
    jmp .end
.sc: mov al, 12
    jmp .end

.w: mov al, 1
    jmp .end
.e: mov al, 3
    jmp .end
.r: jmp .f
    jmp .end
.t: mov al, 6
    jmp .end
.i: mov al, 8
    jmp .end
.o: mov al, 10
    jmp .end
.p: jmp .l
    jmp .end

.z: add ch, 12
    add cl, 1
    mov bh, 2
    jmp .end
.x: sub ch, 12
    sub cl, 1
    mov bh, 2
    jmp .end


.end:
    ret

;--------------------------------------------------
; Set's up the MIDI ports for use
;
; IN: NONE
; OUT: NONE
; ERR: NONE
; REG: DX

setup_midi:
    push ax

    mov dx, MIDI_CONTROL_PORT
    mov al, MIDI_UART_MODE; play notes as soon as they are recieved
    out dx, al

    mov dx, MIDI_DATA_PORT
    mov al, MIDI_PIANO_INSTRUMENT
    out dx, al

    pop ax
    ret

;--------------------------------------------------
; Checks to make sure that input is acceptable
;
; IN: AL = key code
; OUT: BH = 1 (accpetable) or 0 (not acceptable, or octave is trying to change too far)
; ERR: NONE
; REG: preserved

process_input:

.check_key_code:
    cmp al, 'a'
    je .safe
    cmp al, 's'
    je .safe
    cmp al, 'd'
    je .safe
    cmp al, 'f'
    je .safe
    cmp al, 'j'
    je .safe
    cmp al, 'k'
    je .safe
    cmp al, 'l'
    je .safe
    cmp al, ';'
    je .safe

    cmp al, 'w'
    je .safe
    cmp al, 'e'
    je .safe
    cmp al, 'r'
    je .safe
    cmp al, 't'
    je .safe
    cmp al, 'i'
    je .safe
    cmp al, 'o'
    je .safe
    cmp al, 'p'
    je .safe

.check_octave_code:
    cmp al, 'z'
    je .z
    cmp al, 'x'
    je .x

    jmp .err;               none of the keys pressed were valid keys

.z:
    cmp cl, 10;             if user is about to go out of octave range, then drop down to error
    jne .safe

.x:
    cmp cl, 1
    jne .safe

.err:
    xor bh, bh
    ret

.safe:
    mov bh, 1
    ret


;--------------------------------------------------
; Reads a single character from the user
;
; IN: NONE
; OUT: AL = key code
; ERR: NONE
; REG: preserved

read_character:
    xor ah, ah
    int 16h;                BIOS 16h 00h
    ret