107 lines
2.7 KiB
Plaintext
107 lines
2.7 KiB
Plaintext
// ribos2.60p - SixtyPical source for RIBOS2:
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// Demonstration of the VIC-II raster interrupt on the Commodore 64:
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// Alter the border colour in the middle part of the screen only,
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// Simplified (KERNAL IRQ vector) version.
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// SPDX-FileCopyrightText: Chris Pressey, the author of this work, has dedicated it to the public domain.
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// For more information, please refer to <https://unlicense.org/>
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// SPDX-License-Identifier: Unlicense
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// For comments, see ribos2.p65.
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// ----- Types -----
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typedef routine
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inputs border_color, vic_intr, scanline
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outputs border_color, vic_intr, scanline
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trashes a, z, n, c, vic_raster
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irq_handler
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// ----- Addresses -----
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// The CIA #1 chip.
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byte cia1 @ $dc00 // pp. 328-331
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byte intr_ctrl @ $dc0d // "CIA Interrupt Control Register
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// (Read IRQs/Write Mask)"
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// The VIC-II chip.
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byte vic @ $d000 // Appendix G:
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byte vic_ctrl @ $d011 // "Y SCROLL MODE"
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byte vic_raster @ $d012 // "RASTER"
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byte vic_intr @ $d019 // "Interrupt Request's" (sic)
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byte vic_intr_enable @ $d01a // "Interrupt Request MASKS"
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byte border_color @ $d020 // "BORDER COLOR"
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// The address at which the IRQ vector is stored.
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vector irq_handler cinv @ $314 // p. 319, "Vector: Hardware
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// IRQ Interrupt"
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// ----- Variables -----
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vector irq_handler saved_irq_vec
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byte scanline : 85 // %01010101
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// ----- Externals ------
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// An address in ROM which contains "PLA TAY PLA TAX RTI".
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// ribos2.p65 just contains these instructions itself, but
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// generating them as part of a SixtyPical program would not
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// be practical. So we just jump to this location instead.
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define pla_tay_pla_tax_pla_rti routine
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inputs border_color, vic_intr
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outputs border_color, vic_intr
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trashes a, z, n, c
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@ $EA81
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// ----- Interrupt Handler -----
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define our_service_routine irq_handler
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{
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ld a, vic_intr
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st a, vic_intr
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and a, 1
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cmp a, 1
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if not z {
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goto saved_irq_vec
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} else {
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ld a, border_color
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xor a, $ff
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st a, border_color
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ld a, scanline
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xor a, $ff
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st a, scanline
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st a, vic_raster
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trash vic_raster
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goto pla_tay_pla_tax_pla_rti
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}
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}
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// ----- Main Program -----
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define main routine
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inputs cinv, scanline, vic_ctrl, intr_ctrl
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outputs cinv, saved_irq_vec, vic_ctrl, vic_intr_enable
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trashes a, n, z, vic_raster
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{
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with interrupts off {
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copy cinv, saved_irq_vec
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copy our_service_routine, cinv
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ld a, scanline
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st a, vic_raster
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ld a, vic_ctrl
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and a, 127
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st a, vic_ctrl
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ld a, 1
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st a, vic_intr_enable
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ld a, intr_ctrl
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}
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}
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