emailler/drivers/a2_timer.s

; 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.inc"

.export timer_init
.export timer_read
.export timer_seconds


.bss

current_time_value: .res 2


.code

; reset timer to 0
; inputs: none
; outputs: none
timer_init:
  ldax #0
  stax current_time_value
  rts

; 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')
timer_read:
  bit $c082                     ; switch in ROM
  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
  bit $c080                     ; switch in LC bank 2 for R/O
  rts

timer_seconds:
  lda #0
  rts



; -- LICENSE FOR a2_timerc.s --
; The contents of this file are subject to the Mozilla Public License
; Version 1.1 (the "License"); you may not use this file except in
; compliance with the License. You may obtain a copy of the License at
; http://www.mozilla.org/MPL/
;
; Software distributed under the License is distributed on an "AS IS"
; basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the
; License for the specific language governing rights and limitations
; under the License.
;
; The Original Code is ip65.
;
; The Initial Developer of the Original Code is Jonno Downes,
; jonno@jamtronix.com.
; Portions created by the Initial Developer are Copyright (C) 2009
; Jonno Downes. All Rights Reserved.
; -- LICENSE END --