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70 lines
1.7 KiB
ArmAsm
70 lines
1.7 KiB
ArmAsm
;
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; 2022-03-15, Karri Kaksonen
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;
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; clock_t clock (void);
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;
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.export _clock, clock_count
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.interruptor update_clock, 2 ; (low priority)
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.constructor init_clock
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.import sreg: zp
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.import _zonecounter
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.include "atari7800.inc"
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.macpack generic
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.code
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;-----------------------------------------------------------------------------
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; Read the clock counter.
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;
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.proc _clock
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lda #0
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sta sreg+1 ; Promote 24 bits up to 32 bits
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lda clock_count+2
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sta sreg
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ldx clock_count+1
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lda clock_count
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rts
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.endproc
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;-----------------------------------------------------------------------------
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; This interrupt handler increments a 24-bit counter at every video
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; vertical-blanking time.
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; Update the clock only on interrupt while the drawing on screen is on
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; _zonecounter == 1 (from 1st visible scanline to last visible scanline)
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;
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update_clock:
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lda _zonecounter
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and #01
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beq @L1
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inc clock_count
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bne @L1
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inc clock_count+1
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bne @L1
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inc clock_count+2
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@L1: ;clc ; General interrupt was not reset
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rts
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;-----------------------------------------------------------------------------
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; Set time to zero at startup
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;
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.segment "ONCE"
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init_clock:
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lda #0
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sta clock_count+2
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sta clock_count+1
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sta clock_count
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rts
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;-----------------------------------------------------------------------------
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; Store time in 3 bytes
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;
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.bss
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clock_count:
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.res 3
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