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95 lines
2.3 KiB
NASM
95 lines
2.3 KiB
NASM
// A minimal working raster hardware IRQ with clobber-based register savings
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.pc = $801 "Basic"
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:BasicUpstart(main)
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.pc = $80d "Program"
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// Processor port data direction register
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.label PROCPORT_DDR = 0
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// Mask for PROCESSOR_PORT_DDR which allows only memory configuration to be written
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.const PROCPORT_DDR_MEMORY_MASK = 7
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// Processor Port Register controlling RAM/ROM configuration and the datasette
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.label PROCPORT = 1
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// RAM in $A000, $E000 I/O in $D000
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.const PROCPORT_RAM_IO = 5
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.label RASTER = $d012
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.label BORDERCOL = $d020
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.label BGCOL = $d021
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.label VIC_CONTROL = $d011
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// VIC II IRQ Status Register
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.label IRQ_STATUS = $d019
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// VIC II IRQ Enable Register
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.label IRQ_ENABLE = $d01a
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// Bits for the IRQ Status/Enable Registers
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.const IRQ_RASTER = 1
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// CIA#1 Interrupt Status & Control Register
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.label CIA1_INTERRUPT = $dc0d
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// Value that disables all CIA interrupts when stored to the CIA Interrupt registers
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.const CIA_INTERRUPT_CLEAR = $7f
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// The vector used when the HARDWARE serves IRQ interrupts
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.label HARDWARE_IRQ = $fffe
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// The colors of the C64
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.const BLACK = 0
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.const WHITE = 1
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main: {
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// asm
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sei
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// *PROCPORT_DDR = PROCPORT_DDR_MEMORY_MASK
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// Disable kernal & basic
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lda #PROCPORT_DDR_MEMORY_MASK
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sta PROCPORT_DDR
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// *PROCPORT = PROCPORT_RAM_IO
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lda #PROCPORT_RAM_IO
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sta PROCPORT
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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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// *VIC_CONTROL |=$80
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// Set raster line to $100
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lda #$80
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ora VIC_CONTROL
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sta VIC_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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// *HARDWARE_IRQ = &irq
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// Set the IRQ routine
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lda #<irq
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sta HARDWARE_IRQ
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lda #>irq
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sta HARDWARE_IRQ+1
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// asm
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cli
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__b1:
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// (*BORDERCOL)++;
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inc BORDERCOL
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jmp __b1
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}
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// Interrupt Routine
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irq: {
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sta rega+1
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// do_irq()
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jsr do_irq
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// }
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rega:
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lda #00
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rti
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}
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do_irq: {
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// *BGCOL = WHITE
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lda #WHITE
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sta BGCOL
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// *BGCOL = BLACK
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lda #BLACK
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sta BGCOL
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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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rts
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}
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