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Estimate the local/master frequency ratio when free running. 

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
master
Richard Cochran 2012-08-17 19:16:32 +02:00
parent 83bd97be80
commit cd8996ecb9
1 changed files with 52 additions and 0 deletions
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52
clock.c
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@ -41,6 +41,13 @@
#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
struct freq_estimator {
tmv_t origin1;
tmv_t ingress1;
int max_count;
int count;
};
struct clock {
clockid_t clkid;
struct servo *servo;
@ -59,6 +66,7 @@ struct clock {
tmv_t master_offset;
tmv_t path_delay;
struct mave *avg_delay;
struct freq_estimator fest;
tmv_t c1;
tmv_t c2;
tmv_t t1;
@ -114,6 +122,46 @@ static int clock_master_lost(struct clock *c)
return 1;
}
static enum servo_state clock_no_adjust(struct clock *c)
{
double ratio;
struct freq_estimator *f = &c->fest;
enum servo_state state = SERVO_UNLOCKED;
/*
* We have clock.t1 as the origin time stamp, and clock.t2 as
* the ingress. The time at which the master sent the sync is:
*
* origin = origin_ts + path_delay + correction
*
* The ratio of the local clock freqency to the master clock
* is estimated by:
*
* (ingress_2 - ingress_1) / (origin_2 - origin_1)
*
* Both of the origin time estimates include the path delay,
* but we assume that the path delay is in fact constant.
* By leaving out the path delay altogther, we can avoid the
* error caused by our imperfect path delay measurement.
*/
f->count++;
if (f->count < f->max_count) {
return state;
}
if (f->ingress1) {
ratio = (c->t2 - f->ingress1 + 0.0) /
(c->t1 /*+c->path_delay*/ + c->c1 + c->c2 - f->origin1);
pr_info("master offset %10lld s%d ratio %.9f path delay %10lld",
c->master_offset, state, ratio, c->path_delay);
}
f->ingress1 = c->t2;
f->origin1 = c->t1 /*+c->path_delay*/ + c->c1 + c->c2;
f->count = 0;
return state;
}
static void clock_ppb(clockid_t clkid, double ppb)
{
struct timex tx;
@ -266,6 +314,7 @@ struct clock *clock_create(int phc_index, struct interface *iface, int count,
}
c->fault_timeout = FAULT_RESET_SECONDS;
c->fest.max_count = 2;
for (i = 0; i < count; i++) {
c->port[i] = port_open(phc_index, timestamping, 1+i, &iface[i], c);
@ -581,6 +630,9 @@ enum servo_state clock_synchronize(struct clock *c,
if (!c->path_delay)
return state;
if (c->dds.free_running)
return clock_no_adjust(c);
adj = servo_sample(c->servo, c->master_offset, ingress, &state);
pr_info("master offset %10lld s%d adj %+7.0f path delay %10lld",