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.include "atari.inc"
.export _keyclick
; keyclick.s - just what you think it is.
; How do you make it possible to disable the keyclick on the 400/800?
; Don't use the OS K: handler.
;.ifdef REAL_KEYCLICK
.if 1
; Copied from OS ROM source, 12 bytes of code. Because of the repeated
; stx WSYNC, you don't want to use this if you're using DLIs.
; Preserves A and Y, returns with X=$ff, N set, Z clear.
_keyclick:
ldx #$7f
@rc1:
stx CONSOL
stx WSYNC
dex
bpl @rc1
rts
.else
; Fake keyclick. 25 bytes of code. Sounds just like the real one, but
; it won't mess up your DLIs because it's interruptible (though DLIs
; might mess it up). Loop timing assumes a GR.0 type display list
; with playfield DMA enabled and P/M DMA disabled.
; Preserves A, returns with X=$ff, Y=0, N set, Z clear.
_keyclick:
@wcount:
ldx VCOUNT ; To make the timing consistent, wait until we're sure
cpx #$10 ; that ANTIC is doing DMA.
bne @wcount
ldx #$7f
@click: ; I tuned this by ear, then cycle-counted afterward.
stx CONSOL ; 4
ldy #$07 ; 2
;lda #0 ; 2
nop
@c1:
dey ; inner: 2
nop ; 2
bne @c1 ; 3
; 7 cycles/loop, *7 = 49, -1 for failed BNE
; 48
dex ; 2
bpl @click ; 3 = 61
rts
.endif
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