I'm having some issues with my controller code.
Up, down, left and right all work as they should. Any combination of three buttons or more works as expected (opposite directions cancel each other out, up+down+left+right results in no movement). Down+left and down+right also work as expected.
Up+left, however, results in movement up, no left, and up+right results in movement up and double movement right.
Any ideas?
The exact same behavior is observed both in emu and on real hardware.
Up, down, left and right all work as they should. Any combination of three buttons or more works as expected (opposite directions cancel each other out, up+down+left+right results in no movement). Down+left and down+right also work as expected.
Up+left, however, results in movement up, no left, and up+right results in movement up and double movement right.
Any ideas?
Code:
readctrl:
lda #$01
sta $4016
lda #$00
sta $4016
; Read all 8 buttons
ldx #$08
loop:
pha
; Read next button state and mask off low 2 bits.
; Compare with $01, which will set carry flag if
; either or both bits are set.
lda $4016
and #$03
cmp #$01
; Now, rotate the carry flag into the top of A,
; land shift all the other buttons to the right
pla
ror a
dex
bne loop
tax
txa
and #$10 ; up
beq :+
lda #$ff
adc $0204
sta $0204
: txa
and #$20 ; down
beq :+
lda #$01
adc $0204
sta $0204
: txa
and #$40 ; left
beq :+
lda #$ff
adc $0207
sta $0207
: txa
and #$80 ; right
beq :+
lda #$01
adc $0207
sta $0207
lda #$02
sta $4014 ; OAM DMA from RAM page 2
lda #$01
sta $4016
lda #$00
sta $4016
; Read all 8 buttons
ldx #$08
loop:
pha
; Read next button state and mask off low 2 bits.
; Compare with $01, which will set carry flag if
; either or both bits are set.
lda $4016
and #$03
cmp #$01
; Now, rotate the carry flag into the top of A,
; land shift all the other buttons to the right
pla
ror a
dex
bne loop
tax
txa
and #$10 ; up
beq :+
lda #$ff
adc $0204
sta $0204
: txa
and #$20 ; down
beq :+
lda #$01
adc $0204
sta $0204
: txa
and #$40 ; left
beq :+
lda #$ff
adc $0207
sta $0207
: txa
and #$80 ; right
beq :+
lda #$01
adc $0207
sta $0207
lda #$02
sta $4014 ; OAM DMA from RAM page 2
The exact same behavior is observed both in emu and on real hardware.
