24 lines
734 B
ArmAsm
24 lines
734 B
ArmAsm
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
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;; Sequence according to Compute's Mapping the 64 p73
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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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;; Call interrupt routine
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;; (but only if initialised)
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lda $0314
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ora $0315
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beq default_irq_handler
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jmp ($0314)
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