mirror of https://github.com/cc65/cc65.git
88 lines
2.2 KiB
ArmAsm
88 lines
2.2 KiB
ArmAsm
;
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; 2003-04-13, Ullrich von Bassewitz
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; 2012-02-06, Greg King
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;
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; clock_t clock (void);
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; clock_t __clocks_per_sec (void);
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;
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; clocks_per_sec()'s test-values are based on the numbers in "set_tv.s".
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; If you change the numbers there, then change them here, too.
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;
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.export _clock, ___clocks_per_sec, 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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.include "lynx.inc"
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.macpack generic
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.proc _clock
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php
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sei ; Disable interrupts
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; Read the clock counter.
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lda clock_count
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ldx clock_count+1
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ldy clock_count+2
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plp ; Re-enable interrupts
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sty sreg
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stz sreg+1 ; Promote 24 bits up to 32 bits
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rts
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.endproc
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;-----------------------------------------------------------------------------
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; Return the number of clock ticks in one second.
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;
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___clocks_per_sec:
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ldx #$00 ; >50, >60, >75
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ldy PBKUP
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lda #<75
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cpy #$20 + 1
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blt @ok
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lda #<60
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cpy #$29 + 1
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blt @ok
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lda #<50
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@ok: stz sreg ; return 32 bits
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stz sreg+1
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rts
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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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;
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.segment "LOWCODE"
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update_clock:
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lda INTSET
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and #%00000100
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beq @NotVBlank ; Not vertical-blank interrupt
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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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@NotVBlank:
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rts
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;-----------------------------------------------------------------------------
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; Enable the interrupt that update_clock needs.
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;
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.segment "ONCE"
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init_clock:
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lda #%10000000
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tsb VTIMCTLA
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rts
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;-----------------------------------------------------------------------------
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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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