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mockingboard: add interrupt handlre for parts w/o cycle count

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Vince Weaver 2018-10-28 20:30:30 -04:00
parent 4f5b214f60
commit 4767e7e5c5
1 changed files with 52 additions and 0 deletions
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52
megademo/mockingboard.s
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@ -108,8 +108,60 @@ reset_ay_right:
sta MB_VALUE
jsr write_ay_both
;=========================
; Setup Interrupt Handler
;=========================
; Vector address goes to 0x3fe/0x3ff
; FIXME: should chain any existing handler
lda #<interrupt_handler
sta $03fe
lda #>interrupt_handler
sta $03ff
;============================
; Enable 50Hz clock on 6522
;============================
sei ; disable interrupts just in case
lda #$40 ; Continuous interrupts, don't touch PB7
sta $C40B ; ACR register
lda #$7F ; clear all interrupt flags
sta $C40E ; IER register (interrupt enable)
lda #$C0
sta $C40D ; IFR: 1100, enable interrupt on timer one oflow
sta $C40E ; IER: 1100, enable timer one interrupt
lda #$1A
sta $C404 ; write into low-order latch
lda #$41
sta $C405 ; write into high-order latch,
; load both values into counter
; clear interrupt and start counting
; 4fe7 / 1e6 = .020s, 50Hz
; 411a / 1e6 = .016s, 60Hz
rts
interrupt_handler:
; A saved by firmware in $45
txa
pha ; save X
tya
pha ; save Y
jsr play_music
pla
tay ; restore Y
pla
tax ; restore X
lda $45 ; restore A
rti ; return from interrupt ; 6
;=========================================