2009-01-22 01:27:03 +00:00
|
|
|
; timer routines
|
|
|
|
|
;
|
|
|
|
|
; unfortunately the standard Apple 2 has no CIA or VBI, so for the moment, we will
|
|
|
|
|
; make each call to 'timer_read' delay for a little while
|
|
|
|
|
; this kludge will make the polling loops work at least
|
|
|
|
|
;
|
|
|
|
|
; timer_read is meant to return a counter with millisecond resolution
|
|
|
|
|
|
|
|
|
|
.include "../inc/common.i"
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
.export timer_init
|
|
|
|
|
.export timer_read
|
|
|
|
|
|
|
|
|
|
.bss
|
|
|
|
|
current_time_value: .res 2
|
|
|
|
|
|
|
|
|
|
.code
|
|
|
|
|
|
2009-03-21 06:40:53 +00:00
|
|
|
;reset timer to 0
|
|
|
|
|
;inputs: none
|
|
|
|
|
;outputs: none
|
2009-01-22 01:27:03 +00:00
|
|
|
timer_init:
|
|
|
|
|
ldax #0
|
|
|
|
|
stax current_time_value
|
|
|
|
|
rts
|
|
|
|
|
|
2009-03-21 06:40:53 +00:00
|
|
|
;this SHOULD just read the current timer value
|
|
|
|
|
;but since a standard apple 2 has no dedicated timing circuit,
|
|
|
|
|
;each call to this function actually delays a while, then updates the current value
|
|
|
|
|
; inputs: none
|
|
|
|
|
; outputs: AX = current timer value (roughly equal to number of milliseconds since the last call to 'timer_init')
|
2009-01-22 01:27:03 +00:00
|
|
|
timer_read:
|
|
|
|
|
lda #111
|
|
|
|
|
jsr $fca8 ;wait for about 33ms
|
|
|
|
|
clc
|
|
|
|
|
lda #33
|
|
|
|
|
adc current_time_value
|
|
|
|
|
sta current_time_value
|
|
|
|
|
bcc :+
|
|
|
|
|
inc current_time_value+1
|
|
|
|
|
:
|
|
|
|
|
ldax current_time_value
|
|
|
|
|
rts
|
|
|
|
|
|
