tsc.c

一款类linux的操作系统源码

/*
 *  Roadrunner/pk
 *    Copyright (C) 1989-2002  Cornfed Systems, Inc.
 *
 *  The Roadrunner/pk operating system is free software; you can
 *  redistribute and/or modify it under the terms of the GNU General
 *  Public License, version 2, as published by the Free Software
 *  Foundation.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public
 *  License along with this program; if not, write to the Free
 *  Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
 *  MA 02111-1307 USA
 *
 *  More information about the Roadrunner/pk operating system of
 *  which this file is a part is available on the World-Wide Web
 *  at: http://www.cornfed.com.
 *
 */

#include <limits.h>
#include <stdio.h>
#include <sys/time.h>
#include <sys/tsc.h>

static struct tsc cpuspeed;

void
tscsub(tsc_t result, tsc_t cnt1, tsc_t cnt2)
{
    result->hi = 0;
    result->lo = 0;

    if (cnt1->hi == cnt2->hi && cnt1->lo > cnt2->lo)
	result->lo += cnt1->lo - cnt2->lo;

    else if (cnt1->hi > cnt2->hi) {
	result->lo += (UINT_MAX - cnt2->lo);

	if (cnt1->lo <= UINT_MAX - result->lo)
	    result->lo += cnt1->lo + 1;
	else {
	    result->lo = cnt1->lo - (UINT_MAX - result->lo);
	    result->hi++;
	}

	result->hi += cnt1->hi - cnt2->hi - 1;
    }
}

void
tsccalibrate()
{
    struct timeval tv1, tv2;
    struct tsc cnt1, cnt2;

    utime(&(tv1.tv_sec), &(tv1.tv_usec));
    for (;;) {
	utime(&(tv2.tv_sec), &(tv2.tv_usec));
	if (tv2.tv_sec != tv1.tv_sec)
	    break;
    }
    tscread(&cnt1);
    for (;;) {
	utime(&(tv1.tv_sec), &(tv1.tv_usec));
	if (tv1.tv_sec != tv2.tv_sec)
	    break;
    }
    tscread(&cnt2);
    tscsub(&cpuspeed, &cnt2, &cnt1);

    if (cpuspeed.hi > 0)
	kprintf("cpu is faster than 4 GHz\n");
    else if (cpuspeed.lo > 1000000000)
	kprintf("cpu speed %d.%d GHz\n",
		cpuspeed.lo / 1000000000,
		(cpuspeed.lo % 1000000000) / 1000000);
    else
	kprintf("cpu speed %d MHz\n", cpuspeed.lo / 1000000);
}