nes-proj/cpu/6502/clock.c
2007-05-29 22:25:49 +00:00

57 lines
2.7 KiB
C

/*
* Copyright (c) 2007, Swedish Institute of Computer Science.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. 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.
* 3. Neither the name of the Institute nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE 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 INSTITUTE 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.
*
* This file is part of the Contiki operating system.
*
* Author: Oliver Schmidt <ol.sc@web.de>
*
* $Id: clock.c,v 1.2 2007/05/29 22:25:49 oliverschmidt Exp $
*/
#include <time.h>
#include "contiki.h"
/*-----------------------------------------------------------------------------------*/
clock_time_t
clock_time(void)
{
/* Contiki contains quite some calculations based on clock_time_t so we want
* to avoid defining clock_time_t to be 32 bit because that would mean a lot
* of overhead for cc65 targets.
* On the other hand we want to avoid wrapping around frequently so the idea
* is to reduce the clock resolution to the bare minimum. This is defined by
* the TCP/IP stack using a 1/2 second periodic timer. So CLOCK_CONF_SECOND
* needs to be defined at least as 2.
* The value 2 works out especially nicely as it allows us to implement the
* clock frequency devider below purely in (32 bit) integer arithmetic based
* on the educated guess of CLK_TCK being an even value. */
return clock() / (CLK_TCK / CLOCK_CONF_SECOND);
}
/*-----------------------------------------------------------------------------------*/