28 lines
635 B
ArmAsm
28 lines
635 B
ArmAsm
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;;
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;; Official Kernal routine, described in:
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;;
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;; - [RG64] C64 Programmer's Reference Guide - page 299/300
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;; - [CM64] Compute's Mapping the Commodore 64 - page 232
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;;
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;; CPU registers that has to be preserved (see [RG64]): .A, .X, .Y
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;;
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settim:
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;; Disable interrupts for the duration of the routine, to prevent
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;; jiffy clock update while changing it's values
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sei
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;; Store the jiffy clock state
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sty TIME + 0
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stx TIME + 1
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sta TIME + 2
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;; Enable interrupts. More elegant solution would be pha + sei + ... + pla,
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;; but (checked by running a test program) original ROM routine always
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;; leaves IRQs enabled.
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cli
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rts
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