[6502] - Simple game

define player $06
define key $ff
define up $77
define down $73
define left $61
define right $64
define scr $0200
define pos $11
define ppos $12

init:
  lda #$00
  sta $11
  lda #$03
  sta $12

jsr draw
jmp loop

getax:
    lda ppos
rts

getay:
    lda pos
rts

loadp:
    ldx #$00
    sta (pos, X)
rts

undraw:
   lda #$00
   ldx #$00
   sta (pos, X)
rts

negk:
   lda #$00
   sta key
rts

draw:
   lda #player
   jsr loadp
rts

game:
    lda key
    cmp #up
    beq mu
    cmp #down
    beq md
    cmp #left
    beq ml
    cmp #right
    beq mr
    rts
    mu:
        jsr undraw
        ;load y postion into a
        ; adds 1 to screen y
        jsr getay
        sec
        sbc #$20
        sta $11
        ; move if larger than 1 byte
        bcc mua
         jsr negk
         jsr draw
    rts
    mua:
        dec $12
        jsr negk
        jsr draw
    rts
    md:
        jsr undraw
        jsr getay
        clc
        adc #$20
        sta $11
        bcs mda
        jsr negk
        jsr draw
     rts
    mda:
        inc $12
        jsr negk
        jsr draw
    rts
    ml:
       jsr undraw
       dec $11
       jsr negk
       jsr draw
    rts
    mr:
       jsr undraw
       inc $11
       jsr negk
       jsr draw
    rts
rts

loop:
  jsr game
jmp loop