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SubjectRe: how to get cpu_khz?
David Fries wrote:
>
> I'm using the TSC of the Pentium processors to get some precise timing
> delays for writing to a eeprom (bit banging bus operations), and it
> works just fine, but the cpu_khz variable isn't exported to a kernel
> module, so I hardcoded in my module. It works fine for that one
> system, but obviously I don't want to hard code it for the general
> case. I guess I could write my own routine to figure out what the
> cpu_khz is, but it is already done, so how do I get access to it?

I don't know of any official way of doing this, but here's some
code (written by aa) that accomplishes this./*
* $Id: MHz.c,v 1.4 2001/05/21 18:58:01 davej Exp $
* This file is part of x86info.
* (C) 2001 Dave Jones.
*
* Licensed under the terms of the GNU GPL License version 2.
*
* Estimate CPU MHz routine by Andrea Arcangeli <andrea@suse.de>
* Small changes by David Sterba <sterd9am@ss1000.ms.mff.cuni.cz>
*
*/

#include <stdio.h>
#include <sys/time.h>
#include <string.h>
#include <unistd.h>

__inline__ unsigned long long int rdtsc()
{
unsigned long long int x;
__asm__ volatile (".byte 0x0f, 0x31" : "=A" (x));
return x;
}

void estimate_MHz()
{
struct timezone tz;
struct timeval tvstart, tvstop;
unsigned long long int cycles[2]; /* gotta be 64 bit */
unsigned int microseconds; /* total time taken */

memset(&tz, 0, sizeof(tz));

/* get this function in cached memory */
gettimeofday(&tvstart, &tz);
cycles[0] = rdtsc();
gettimeofday(&tvstart, &tz);

/* we don't trust that this is any specific length of time */
usleep(1000000);

cycles[1] = rdtsc();
gettimeofday(&tvstop, &tz);
microseconds = ((tvstop.tv_sec-tvstart.tv_sec)*1000000) +
(tvstop.tv_usec-tvstart.tv_usec);

printf("%lldMHz processor (estimate).\n",
(cycles[1]-cycles[0])/microseconds);
}

int main(void)
{
while (1) {
estimate_MHz();
}
return (0);
}
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