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Add a method to estimate the PHC to system offset using the new ioctl.

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Signed-off-by: Richard Cochran <richardcochran@gmail.com>
This commit is contained in:
Richard Cochran 2012-11-26 13:22:07 +01:00
parent 60ca52a3fc
commit 36a5224b5a
2 changed files with 156 additions and 0 deletions
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/**
* @file sysoff.c
* @brief Implements the system offset estimation method.
* @note Copyright (C) 2012 Richard Cochran <richardcochran@gmail.com>
*
* 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 Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include <stdio.h>
#include <sys/ioctl.h>
#include <linux/ptp_clock.h>
#include "sysoff.h"
#define NS_PER_SEC 1000000000LL
#ifdef PTP_SYS_OFFSET
static int64_t pctns(struct ptp_clock_time *t)
{
return t->sec * NS_PER_SEC + t->nsec;
}
static struct {
int64_t interval;
int64_t offset;
uint64_t timestamp;
} samples[PTP_MAX_SAMPLES];
static void insertion_sort(int length, int64_t interval, int64_t offset, uint64_t ts)
{
int i = length - 1;
while (i >= 0) {
if (samples[i].interval < interval)
break;
samples[i+1] = samples[i];
i--;
}
samples[i+1].interval = interval;
samples[i+1].offset = offset;
samples[i+1].timestamp = ts;
}
static int64_t sysoff_estimate(struct ptp_clock_time *pct, int n_samples, uint64_t *ts)
{
int64_t t1, t2, tp;
int64_t interval, offset;
int i;
for (i = 0; i < n_samples; i++) {
t1 = pctns(&pct[2*i]);
tp = pctns(&pct[2*i+1]);
t2 = pctns(&pct[2*i+2]);
interval = t2 - t1;
offset = (t2 + t1) / 2 - tp;
insertion_sort(i, interval, offset, (t2 + t1) / 2);
}
*ts = samples[0].timestamp;
return samples[0].offset;
}
int sysoff_measure(int fd, int n_samples, int64_t *result, uint64_t *ts)
{
struct ptp_sys_offset pso;
pso.n_samples = n_samples;
if (ioctl(fd, PTP_SYS_OFFSET, &pso)) {
perror("ioctl PTP_SYS_OFFSET");
return SYSOFF_RUN_TIME_MISSING;
}
*result = sysoff_estimate(pso.ts, n_samples, ts);
return SYSOFF_SUPPORTED;
}
int sysoff_probe(int fd, int n_samples)
{
int64_t junk;
uint64_t ts;
if (n_samples > PTP_MAX_SAMPLES) {
fprintf(stderr, "warning: %d exceeds kernel max readings %d\n",
n_samples, PTP_MAX_SAMPLES);
fprintf(stderr, "falling back to clock_gettime method\n");
return SYSOFF_RUN_TIME_MISSING;
}
return sysoff_measure(fd, n_samples, &junk, &ts);
}
#else /* !PTP_SYS_OFFSET */
int sysoff_measure(int fd, int n_samples, int64_t *result, uint64_t *ts)
{
return SYSOFF_COMPILE_TIME_MISSING;
}
int sysoff_probe(int fd, int n_samples)
{
return SYSOFF_COMPILE_TIME_MISSING;
}
#endif /* PTP_SYS_OFFSET */

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/**
* @file sysoff.h
* @brief Implements the system offset estimation method.
* @note Copyright (C) 2012 Richard Cochran <richardcochran@gmail.com>
*
* 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 Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include <stdint.h>
enum {
SYSOFF_SUPPORTED,
SYSOFF_COMPILE_TIME_MISSING,
SYSOFF_RUN_TIME_MISSING,
};
/**
* Check to see if the PTP_SYS_OFFSET ioctl is supported.
* @param fd An open file descriptor to a PHC device.
* @return One of the SYSOFF_ enumeration values.
*/
int sysoff_probe(int fd, int n_samples);
/**
* Measure the offset between a PHC and the system time.
* @param fd An open file descriptor to a PHC device.
* @param n_samples The number of consecutive readings to make.
* @param result The estimated offset in nanoseconds.
* @param ts The system time corresponding to the 'result'.
* @return One of the SYSOFF_ enumeration values.
*/
int sysoff_measure(int fd, int n_samples, int64_t *result, uint64_t *ts);