systime.c

/*
 *  systime.c
 *  Stripped down time services from BrickOS
 *
 *  The contents of this file are subject to the Mozilla Public License
 *  Version 1.0 (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 legOS code, released October 17, 1999.
 *
 *  The Initial Developer of the Original Code is Markus L. Noga.
 *  Portions created by Markus L. Noga are Copyright (C) 1999
 *  Markus L. Noga. All Rights Reserved.
 *
 *  Contributor(s): Markus L. Noga <markus@noga.de>
 *                  David Van Wagner <davevw@alumni.cse.ucsc.edu>
 *                  Jon Simpson <me@jonsimpson.co.uk>
 */

#include "systime.h"

/**
 * sys_time should be initialized every
 * time a new program is started.
 */
volatile unsigned long sys_time;

/***
 * the systime_handler doesn't do too much. After all, its gotta
 * run every millisecond. What we do can perhaps be best described
 * as "borrowing" the OCIA interrupt. Because, the first thing we
 * do is call the default ROM handler. This causes the rom to do
 * a bunch of stuff for us (IR communication, sensor, motor, sound, to
 * name a few.) After its done, we increment our time counter, and 
 * then return. 
 */
__asm__(
".text\n"
".align 1\n"
".global _systime_handler\n"
"_systime_handler:\n"
"                ; r6 saved by ROM\n"
"\n"
"                ; call the ROM OCIA handler\n"
"                jsr     _rom_ocia_handler \n"
"\n"
"                ; increment system timer\n"
"                mov.w @_sys_time+2,r6          ; LSW -> r6\n"
"                add.b #0x1,r6l                 ; 16 bit: add 1\n"
"                addx  #0x0,r6h\n"
"                mov.w r6,@_sys_time+2\n"
"                bcc sys_nohigh                 ; speedup for 65535 cases\n"
"                  mov.w @_sys_time,r6          ; MSW -> r6\n"
"                  add.b #0x1,r6l\n"
"                  addx  #0x0,r6h\n"
"                  mov.w r6,@_sys_time\n"
"              sys_nohigh:\n"
"\n"
/*"                ; set tick request\n"
"                mov.b #0x1,r6l\n"
"                mov.b r6l,@_gMakeRequest\n"
"\n"
*/
"                ;bclr    #3,@0x91:8        ; reset compare A IRQ flag\n"
"                rts\n"
);