source: trunk/udelay.c @ 1280

/*
 * This file is part of the flashrom project.
 *
 * Copyright (C) 2000 Silicon Integrated System Corporation
 * Copyright (C) 2009,2010 Carl-Daniel Hailfinger
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY 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., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
 */

#ifndef __LIBPAYLOAD__

#include <unistd.h>
#include <sys/time.h>
#include <stdlib.h>
#include <limits.h>
#include "flash.h"

/* loops per microsecond */
static unsigned long micro = 1;

__attribute__ ((noinline)) void myusec_delay(int usecs)
{
        unsigned long i;
        for (i = 0; i < usecs * micro; i++) {
                /* Make sure the compiler doesn't optimize the loop away. */
                asm volatile ("" : : "rm" (i) );
        }
}

static unsigned long measure_os_delay_resolution(void)
{
        unsigned long timeusec;
        struct timeval start, end;
        unsigned long counter = 0;
        
        gettimeofday(&start, NULL);
        timeusec = 0;
        
        while (!timeusec && (++counter < 1000000000)) {
                gettimeofday(&end, NULL);
                timeusec = 1000000 * (end.tv_sec - start.tv_sec) +
                           (end.tv_usec - start.tv_usec);
                /* Protect against time going forward too much. */
                if ((end.tv_sec > start.tv_sec) &&
                    ((end.tv_sec - start.tv_sec) >= LONG_MAX / 1000000 - 1))
                        timeusec = 0;
                /* Protect against time going backwards during leap seconds. */
                if ((end.tv_sec < start.tv_sec) || (timeusec > LONG_MAX))
                        timeusec = 0;
        }
        return timeusec;
}

static unsigned long measure_delay(int usecs)
{
        unsigned long timeusec;
        struct timeval start, end;
        
        gettimeofday(&start, NULL);
        myusec_delay(usecs);
        gettimeofday(&end, NULL);
        timeusec = 1000000 * (end.tv_sec - start.tv_sec) +
                   (end.tv_usec - start.tv_usec);
        /* Protect against time going forward too much. */
        if ((end.tv_sec > start.tv_sec) &&
            ((end.tv_sec - start.tv_sec) >= LONG_MAX / 1000000 - 1))
                timeusec = LONG_MAX;
        /* Protect against time going backwards during leap seconds. */
        if ((end.tv_sec < start.tv_sec) || (timeusec > LONG_MAX))
                timeusec = 1;

        return timeusec;
}

void myusec_calibrate_delay(void)
{
        unsigned long count = 1000;
        unsigned long timeusec, resolution;
        int i, tries = 0;

        msg_pinfo("Calibrating delay loop... ");
        resolution = measure_os_delay_resolution();
        if (resolution) {
                msg_pdbg("OS timer resolution is %lu usecs, ", resolution);
        } else {
                msg_pinfo("OS timer resolution is unusable. ");
        }

recalibrate:
        count = 1000;
        while (1) {
                timeusec = measure_delay(count);
                if (timeusec > 1000000 / 4)
                        break;
                if (count >= ULONG_MAX / 2) {
                        msg_pinfo("timer loop overflow, reduced precision. ");
                        break;
                }
                count *= 2;
        }
        tries ++;

        /* Avoid division by zero, but in that case the loop is shot anyway. */
        if (!timeusec)
                timeusec = 1;
        
        /* Compute rounded up number of loops per microsecond. */
        micro = (count * micro) / timeusec + 1;
        msg_pdbg("%luM loops per second, ", micro);

        /* Did we try to recalibrate less than 5 times? */
        if (tries < 5) {
                /* Recheck our timing to make sure we weren't just hitting
                 * a scheduler delay or something similar.
                 */
                for (i = 0; i < 4; i++) {
                        if (resolution && (resolution < 10)) {
                                timeusec = measure_delay(100);
                        } else if (resolution && 
                                   (resolution < ULONG_MAX / 200)) {
                                timeusec = measure_delay(resolution * 10) *
                                           100 / (resolution * 10);
                        } else {
                                /* This workaround should be active for broken
                                 * OS and maybe libpayload. The criterion
                                 * here is horrible or non-measurable OS timer
                                 * resolution which will result in
                                 * measure_delay(100)=0 whereas a longer delay
                                 * (1000 ms) may be sufficient
                                 * to get a nonzero time measurement.
                                 */
                                timeusec = measure_delay(1000000) / 10000;
                        }
                        if (timeusec < 90) {
                                msg_pdbg("delay more than 10%% too short (got "
                                         "%lu%% of expected delay), "
                                         "recalculating... ", timeusec);
                                goto recalibrate;
                        }
                }
        } else {
                msg_perr("delay loop is unreliable, trying to continue ");
        }

        /* We're interested in the actual precision. */
        timeusec = measure_delay(10);
        msg_pdbg("10 myus = %ld us, ", timeusec);
        timeusec = measure_delay(100);
        msg_pdbg("100 myus = %ld us, ", timeusec);
        timeusec = measure_delay(1000);
        msg_pdbg("1000 myus = %ld us, ", timeusec);
        timeusec = measure_delay(10000);
        msg_pdbg("10000 myus = %ld us, ", timeusec);
        timeusec = measure_delay(resolution * 4);
        msg_pdbg("%ld myus = %ld us, ", resolution * 4, timeusec);

        msg_pinfo("OK.\n");
}

void internal_delay(int usecs)
{
        /* If the delay is >1 s, use usleep because timing does not need to
         * be so precise.
         */
        if (usecs > 1000000) {
                usleep(usecs);
        } else {
                myusec_delay(usecs);
        }
}

#else 
#include <libpayload.h>

void myusec_calibrate_delay(void)
{
        get_cpu_speed();
}

void internal_delay(int usecs)
{
        udelay(usecs);
}
#endif