4cade/src/hw.vidhd.a
2019-10-12 13:10:58 -04:00

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;license:MIT
;(c) 2018-9 by 4am
;
; VidHD support functions
;
;------------------------------------------------------------------------------
; HasVidHDCard
; detect VidHD card by searching for magic bytes across all slots
;
; in: none
; out: C set if VidHD card found in any slot
; if card was found, X = #$Cn where n is the slot number of the card
; C clear if no VidHD card found
; other flags clobbered
; A/Y clobbered
;------------------------------------------------------------------------------
HasVidHDCard
ldx #$C7
@slotLoop
stx @byteLoop+2
ldy #$02
@byteLoop
lda $FD00, y ; SMC (high byte)
cmp @kVidHDMagicBytes, y
bne @nextSlot
dey
bpl @byteLoop
@found
sec ; found
rts
@nextSlot
dex
cpx #$C0
bne @slotLoop
clc ; not found
rts
@kVidHDMagicBytes
!byte $24, $EA, $4C