71 lines
1.7 KiB
ArmAsm
71 lines
1.7 KiB
ArmAsm
; timer routines
|
|
;
|
|
; the timer should be a 16-bit counter that's incremented by about
|
|
; 1000 units per second. it doesn't have to be particularly accurate.
|
|
|
|
.include "../inc/common.inc"
|
|
|
|
.export timer_init
|
|
.export timer_read
|
|
.export timer_seconds ; this should return a single BCD byte (00..59) which is a count of seconds
|
|
|
|
|
|
.code
|
|
|
|
; initialize timers
|
|
timer_init:
|
|
lda #$80 ; stop timers
|
|
sta $dd0e
|
|
sta $dd0f
|
|
|
|
ldax #999 ; timer A to 1000 cycles
|
|
stax $dd04
|
|
|
|
ldax #$ffff ; timer B to max cycles
|
|
stax $dd06
|
|
|
|
lda #$81 ; timer A in continuous mode
|
|
sta $dd0e
|
|
|
|
lda #$c1 ; timer B to count timer A underflows
|
|
sta $dd0f
|
|
|
|
lda #0
|
|
sta $dc08
|
|
sta $dc09
|
|
rts
|
|
|
|
timer_seconds:
|
|
lda $dc09
|
|
rts
|
|
|
|
; return the current value
|
|
timer_read:
|
|
lda $dd07 ; cia counts backwards, return inverted value
|
|
eor #$ff
|
|
tax
|
|
lda $dd06
|
|
eor #$ff
|
|
rts
|
|
|
|
|
|
|
|
; -- LICENSE FOR c64timer.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 --
|