/*
 * (c)2012 Michael Duane Rice All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer. Redistributions in binary
 * form must reproduce the above copyright notice, this list of conditions
 * and the following disclaimer in the documentation and/or other materials
 * provided with the distribution. Neither the name of the copyright holders
 * nor the names of contributors may be used to endorse or promote products
 * derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/* $Id: system_tick.S 2348 2013-04-16 23:42:05Z swfltek $ */

/*
    Impoved system_tick Credit to Wouter van Gulik.
*/

#include <avr/common.h>

    .global	system_tick
	.type	system_tick, @function
system_tick:
    push r24
    in r24,_SFR_IO_ADDR(SREG)
	push r24
	cli
    lds r24,__system_time+0
    subi r24, (-1)
    sts __system_time+0,r24
    lds r24,__system_time+1
    sbci r24, (-1)
    sts __system_time+1,r24
    lds r24,__system_time+2
    sbci r24, (-1)
    sts __system_time+2,r24
    lds r24,__system_time+3
    sbci r24, (-1)
    sts __system_time+3,r24
    pop r24
    out _SFR_IO_ADDR(SREG),r24
    pop r24
    ret
	.size	system_tick, .-system_tick