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- Tab chars were partially used with the unusual width of two blanks. I removed them altogether. - Line endings were inconsistent even iniside individual files. I normalized them. - I introduced a consistent coding style regarding comment indenting and blank line usage. - I removed trailing spaces. - I removed newlines following unnamed labels. - ...
71 lines
1.7 KiB
ArmAsm
71 lines
1.7 KiB
ArmAsm
; timer routines
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;
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; the timer should be a 16-bit counter that's incremented by about
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; 1000 units per second. it doesn't have to be particularly accurate.
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.include "../inc/common.i"
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.export timer_init
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.export timer_read
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.export timer_seconds ; this should return a single BCD byte (00..59) which is a count of seconds
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.code
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; initialize timers
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timer_init:
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lda #$80 ; stop timers
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sta $dd0e
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sta $dd0f
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ldax #999 ; timer A to 1000 cycles
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stax $dd04
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ldax #$ffff ; timer B to max cycles
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stax $dd06
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lda #$81 ; timer A in continuous mode
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sta $dd0e
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lda #$c1 ; timer B to count timer A underflows
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sta $dd0f
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lda #0
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sta $dc08
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sta $dc09
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rts
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timer_seconds:
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lda $dc09
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rts
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; return the current value
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timer_read:
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lda $dd07 ; cia counts backwards, return inverted value
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eor #$ff
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tax
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lda $dd06
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eor #$ff
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rts
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; -- LICENSE FOR c64timer.s --
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; The contents of this file are subject to the Mozilla Public License
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; Version 1.1 (the "License"); you may not use this file except in
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; compliance with the License. You may obtain a copy of the License at
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; http://www.mozilla.org/MPL/
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;
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; Software distributed under the License is distributed on an "AS IS"
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; basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the
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; License for the specific language governing rights and limitations
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; under the License.
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;
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; The Original Code is ip65.
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;
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; The Initial Developer of the Original Code is Jonno Downes,
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; jonno@jamtronix.com.
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; Portions created by the Initial Developer are Copyright (C) 2009
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; Jonno Downes. All Rights Reserved.
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; -- LICENSE END --
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