28 lines
857 B
ArmAsm
28 lines
857 B
ArmAsm
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irq_handler:
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;; The IRQ is a commonly messed with thing on the C64,
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;; so we need to handle entry points that are commonly
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;; relied upon, including:
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;; $EA31 - Standard IRQ routine
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;; $EA61 - Check keyboard, but don't update timer? https://github.com/cc65/cc65/issues/324
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;; $EA81 - https://www.lemon64.com/forum/viewtopic.php?t=2112&sid=6ea01982b26da69783120a7923ca46fb
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;; Also the $0314 vector is widely used (e.g., https://www.lemon64.com/forum/viewtopic.php?t=2112&sid=6ea01982b26da69783120a7923ca46fb)
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;; Save registers, sequence according to Compute's Mapping the Commodore 64, page 73
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pha
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txa
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pha
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tya
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pha
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;; XXX check if caused by BRK, react accordingly
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;; Call interrupt routine (only if initialised)
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lda CINV
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ora CINV+1
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bne +
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jmp (CINV)
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*
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;; Vector not initialized - call default interrupt routine
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jmp default_irq_handler
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