42 lines
847 B
ArmAsm
42 lines
847 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 303
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// - [CM64] Compute's Mapping the Commodore 64 - pages 27, 232
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//
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// CPU registers that has to be preserved (see [RG64]): .Y
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//
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UDTIM:
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// Update jiffy clock. The whole day is $4F1A00 jiffies
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// (24 hours * 60 minutes * 60 seconds * 60 jiffies),
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// after this time we have to reset the clock.
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inc TIME+0
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bne udtim_time_done // done with clock
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inc TIME+1
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bne udtim_clock_rollover
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inc TIME+2
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// FALLTROUGH
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udtim_time_done:
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jmp udtim_keyboard
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udtim_clock_rollover:
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// At this point TIME+0 contains 0
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lda TIME+1
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cmp #$1A
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bne udtim_time_done // done with clock
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lda TIME+2
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cmp #$4F
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bne udtim_time_done // done with clock
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lda #$00
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sta TIME+2
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sta TIME+1
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beq udtim_time_done // done with clock - will always jump
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