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