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lib/timeutil: add utilities to manage local/reference clock alignment

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Provide data structures to capture a timestamp in two different
clocks, monitor the drift between those clocks, and using a base
instant with estimated drift convert between the clocks.

This provides the core technology to convert between system uptime and
an external continuous time scale like TAI (UTC without applying leap
seconds).

Signed-off-by: Peter A. Bigot <pab@pabigot.com>
This commit is contained in:
Peter A. Bigot 2020-08-01 13:25:58 -05:00 • committed by Anas Nashif
commit f6d7595d4e
7 changed files with 742 additions and 5 deletions
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108
lib/os/timeutil.c
View file

@ -12,6 +12,7 @@
#include <zephyr/types.h>
#include <errno.h>
#include <stddef.h>
#include <sys/timeutil.h>
/** Convert a civil (proleptic Gregorian) date to days relative to
@ -66,5 +67,112 @@ time_t timeutil_timegm(const struct tm *tm)
errno = ERANGE;
rv = -1;
}
return rv;
}
int timeutil_sync_state_update(struct timeutil_sync_state *tsp,
const struct timeutil_sync_instant *inst)
{
int rv = -EINVAL;
if (((tsp->base.ref == 0) && (inst->ref > 0))
|| ((inst->ref > tsp->base.ref)
&& (inst->local > tsp->base.local))) {
if (tsp->base.ref == 0) {
tsp->base = *inst;
tsp->latest = (struct timeutil_sync_instant){};
tsp->skew = 1.0;
rv = 0;
} else {
tsp->latest = *inst;
rv = 1;
}
}
return rv;
}
int timeutil_sync_state_set_skew(struct timeutil_sync_state *tsp, float skew,
const struct timeutil_sync_instant *base)
{
int rv = -EINVAL;
if (skew > 0) {
tsp->skew = skew;
if (base != NULL) {
tsp->base = *base;
tsp->latest = (struct timeutil_sync_instant){};
}
rv = 0;
}
return rv;
}
float timeutil_sync_estimate_skew(const struct timeutil_sync_state *tsp)
{
float rv = 0;
if ((tsp->base.ref != 0) && (tsp->latest.ref != 0)
&& (tsp->latest.local > tsp->base.local)) {
const struct timeutil_sync_config *cfg = tsp->cfg;
double ref_delta = tsp->latest.ref - tsp->base.ref;
double local_delta = tsp->latest.local - tsp->base.local;
rv = ref_delta * cfg->local_Hz / local_delta / cfg->ref_Hz;
}
return rv;
}
int timeutil_sync_ref_from_local(const struct timeutil_sync_state *tsp,
uint64_t local, uint64_t *refp)
{
int rv = -EINVAL;
if ((tsp->skew > 0) && (tsp->base.ref > 0) && (refp != NULL)) {
const struct timeutil_sync_config *cfg = tsp->cfg;
int64_t local_delta = local - tsp->base.local;
int64_t ref_delta = (int64_t)(tsp->skew * local_delta) *
cfg->ref_Hz / cfg->local_Hz;
int64_t ref_abs = (int64_t)tsp->base.ref + ref_delta;
if (ref_abs < 0) {
rv = -ERANGE;
} else {
*refp = ref_abs;
rv = (int)(tsp->skew != 1.0);
}
}
return rv;
}
int timeutil_sync_local_from_ref(const struct timeutil_sync_state *tsp,
uint64_t ref, int64_t *localp)
{
int rv = -EINVAL;
if ((tsp->skew > 0) && (tsp->base.ref > 0) && (localp != NULL)) {
const struct timeutil_sync_config *cfg = tsp->cfg;
int64_t ref_delta = (int64_t)(ref - tsp->base.ref);
double local_delta = (ref_delta * cfg->local_Hz) / cfg->ref_Hz
/ tsp->skew;
int64_t local_abs = (int64_t)tsp->base.local
+ (int64_t)local_delta;
*localp = local_abs;
rv = (int)(tsp->skew != 1.0);
}
return rv;
}
int32_t timeutil_sync_skew_to_ppb(float skew)
{
int64_t ppb64 = (int64_t)((1.0 - skew) * 1E9);
int32_t ppb32 = (int32_t)ppb64;
return (ppb64 == ppb32) ? ppb32 : INT32_MIN;
}