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67 lines
1.4 KiB
NASM
67 lines
1.4 KiB
NASM
// A minimal working raster IRQ
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// Commodore 64 PRG executable file
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.file [name="irq-kernel.prg", type="prg", segments="Program"]
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.segmentdef Program [segments="Basic, Code, Data"]
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.segmentdef Basic [start=$0801]
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.segmentdef Code [start=$80d]
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.segmentdef Data [startAfter="Code"]
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.segment Basic
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:BasicUpstart(main)
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.const IRQ_RASTER = 1
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.const WHITE = 1
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.const BLACK = 0
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.const CIA_INTERRUPT_CLEAR = $7f
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.label KERNEL_IRQ = $314
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.label RASTER = $d012
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.label VICII_CONTROL = $d011
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.label IRQ_STATUS = $d019
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.label IRQ_ENABLE = $d01a
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.label BG_COLOR = $d020
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.label CIA1_INTERRUPT = $dc0d
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.segment Code
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// Interrupt Routine
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irq: {
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// *BG_COLOR = WHITE
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lda #WHITE
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sta BG_COLOR
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// *BG_COLOR = BLACK
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lda #BLACK
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sta BG_COLOR
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// *IRQ_STATUS = IRQ_RASTER
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// Acknowledge the IRQ
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lda #IRQ_RASTER
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sta IRQ_STATUS
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// }
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jmp $ea31
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}
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main: {
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// asm
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sei
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// *CIA1_INTERRUPT = CIA_INTERRUPT_CLEAR
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// Disable CIA 1 Timer IRQ
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lda #CIA_INTERRUPT_CLEAR
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sta CIA1_INTERRUPT
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// *VICII_CONTROL |=$80
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// Set raster line to $100
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lda #$80
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ora VICII_CONTROL
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sta VICII_CONTROL
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// *RASTER = $00
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lda #0
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sta RASTER
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// *IRQ_ENABLE = IRQ_RASTER
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// Enable Raster Interrupt
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lda #IRQ_RASTER
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sta IRQ_ENABLE
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// *KERNEL_IRQ = &irq
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// Set the IRQ routine
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lda #<irq
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sta KERNEL_IRQ
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lda #>irq
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sta KERNEL_IRQ+1
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// asm
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cli
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// }
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rts
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}
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