mirror of
https://github.com/cc65/cc65.git
synced 2024-06-01 13:41:34 +00:00
70 lines
1.7 KiB
ArmAsm
70 lines
1.7 KiB
ArmAsm
;
|
|
; 2022-03-15, Karri Kaksonen
|
|
;
|
|
; clock_t clock (void);
|
|
;
|
|
|
|
.export _clock, clock_count
|
|
.interruptor update_clock, 2 ; (low priority)
|
|
.constructor init_clock
|
|
|
|
.import sreg: zp
|
|
.import _zonecounter
|
|
.include "atari7800.inc"
|
|
|
|
.macpack generic
|
|
|
|
.code
|
|
|
|
;-----------------------------------------------------------------------------
|
|
; Read the clock counter.
|
|
;
|
|
.proc _clock
|
|
|
|
lda #0
|
|
sta sreg+1 ; Promote 24 bits up to 32 bits
|
|
lda clock_count+2
|
|
sta sreg
|
|
ldx clock_count+1
|
|
lda clock_count
|
|
|
|
rts
|
|
.endproc
|
|
|
|
;-----------------------------------------------------------------------------
|
|
; This interrupt handler increments a 24-bit counter at every video
|
|
; vertical-blanking time.
|
|
; Update the clock only on interrupt while the drawing on screen is on
|
|
; _zonecounter == 1 (from 1st visible scanline to last visible scanline)
|
|
;
|
|
update_clock:
|
|
lda _zonecounter
|
|
and #01
|
|
beq @L1
|
|
inc clock_count
|
|
bne @L1
|
|
inc clock_count+1
|
|
bne @L1
|
|
inc clock_count+2
|
|
@L1: ;clc ; General interrupt was not reset
|
|
rts
|
|
|
|
;-----------------------------------------------------------------------------
|
|
; Set time to zero at startup
|
|
;
|
|
.segment "ONCE"
|
|
init_clock:
|
|
lda #0
|
|
sta clock_count+2
|
|
sta clock_count+1
|
|
sta clock_count
|
|
rts
|
|
|
|
;-----------------------------------------------------------------------------
|
|
; Store time in 3 bytes
|
|
;
|
|
.bss
|
|
clock_count:
|
|
.res 3
|
|
|