Time Synchronization APIs

Data Structures
struct	timeutil_sync_config
	Immutable state for synchronizing two clocks. More...
struct	timeutil_sync_instant
	Representation of an instant in two time scales. More...
struct	timeutil_sync_state
	State required to convert instants between time scales. More...

Functions
int	timeutil_sync_state_update (struct timeutil_sync_state *tsp, const struct timeutil_sync_instant *inst)
	Record a new instant in the time synchronization state.
int	timeutil_sync_state_set_skew (struct timeutil_sync_state *tsp, float skew, const struct timeutil_sync_instant *base)
	Update the state with a new skew and possibly base value.
float	timeutil_sync_estimate_skew (const struct timeutil_sync_state *tsp)
	Estimate the skew based on current state.
int	timeutil_sync_ref_from_local (const struct timeutil_sync_state *tsp, uint64_t local, uint64_t *refp)
	Interpolate a reference timescale instant from a local instant.
int	timeutil_sync_local_from_ref (const struct timeutil_sync_state *tsp, uint64_t ref, int64_t *localp)
	Interpolate a local timescale instant from a reference instant.
int32_t	timeutil_sync_skew_to_ppb (float skew)
	Convert from a skew to an error in parts-per-billion.

Detailed Description

Function Documentation

timeutil_sync_estimate_skew()

float timeutil_sync_estimate_skew

(

const struct timeutil_sync_state *

tsp

)

#include <zephyr/sys/timeutil.h>

Estimate the skew based on current state.

Using the base and latest syncpoints from the state determine the skew of the local clock relative to the reference clock. See timeutil_sync_state::skew.

Parameters

tsp	pointer to a time synchronization state. The base and latest syncpoints must be present and the latest syncpoint must be after the base point in the local time scale.

Returns

the estimated skew, or zero if skew could not be estimated.

timeutil_sync_local_from_ref()

int timeutil_sync_local_from_ref	(	const struct timeutil_sync_state *	tsp,
		uint64_t	ref,
		int64_t *	localp
	)

#include <zephyr/sys/timeutil.h>

Interpolate a local timescale instant from a reference instant.

Parameters

tsp	pointer to a time synchronization state. This must have a base and a skew installed.
ref	an instant measured in the reference timescale. This may be before or after the base instant.
localp	where the corresponding instant in the local timescale should be stored. An interpolated value before local time 0 is provided without error. If interpolation fails the referenced object is not modified.

Return values

0	if successful with a skew of 1
1	if successful with a skew not equal to 1
-EINVAL	the time synchronization state is not adequately initialized refp is null

timeutil_sync_ref_from_local()

int timeutil_sync_ref_from_local	(	const struct timeutil_sync_state *	tsp,
		uint64_t	local,
		uint64_t *	refp
	)

#include <zephyr/sys/timeutil.h>

Interpolate a reference timescale instant from a local instant.

Parameters

tsp	pointer to a time synchronization state. This must have a base and a skew installed.
local	an instant measured in the local timescale. This may be before or after the base instant.
refp	where the corresponding instant in the reference timescale should be stored. A negative interpolated reference time produces an error. If interpolation fails the referenced object is not modified.

Return values

0	if interpolated using a skew of 1
1	if interpolated using a skew not equal to 1
-EINVAL	the times synchronization state is not adequately initialized refp is null
-ERANGE	the interpolated reference time would be negative

timeutil_sync_skew_to_ppb()

int32_t timeutil_sync_skew_to_ppb

(

float

skew

)

#include <zephyr/sys/timeutil.h>

Convert from a skew to an error in parts-per-billion.

A skew of 1.0 has zero error. A skew less than 1 has a positive error (clock is faster than it should be). A skew greater than one has a negative error (clock is slower than it should be).

Note that due to the limited precision of float compared with double the smallest error that can be represented is about 120 ppb. A "precise" time source may have error on the order of 2000 ppb.

A skew greater than 3.14748 may underflow the 32-bit representation; this represents a clock running at less than 1/3 its nominal rate.

Returns

skew error represented as parts-per-billion, or INT32_MIN if the skew cannot be represented in the return type.

timeutil_sync_state_set_skew()

int timeutil_sync_state_set_skew	(	struct timeutil_sync_state *	tsp,
		float	skew,
		const struct timeutil_sync_instant *	base
	)

#include <zephyr/sys/timeutil.h>

Update the state with a new skew and possibly base value.

Set the skew from a value retrieved from persistent storage, or calculated based on recent skew estimations including from timeutil_sync_estimate_skew().

Optionally update the base timestamp. If the base is replaced the latest instant will be cleared until timeutil_sync_state_update() is invoked.

Parameters

tsp	pointer to a time synchronization state.
skew	the skew to be used. The value must be positive and shouldn't be too far away from 1.
base	optional new base to be set. If provided this becomes the base timestamp that will be used along with skew to convert between reference and local timescale instants. Setting the base clears the captured latest value.

Returns

0 if skew was updated

-EINVAL if skew was not valid

timeutil_sync_state_update()

int timeutil_sync_state_update	(	struct timeutil_sync_state *	tsp,
		const struct timeutil_sync_instant *	inst
	)

#include <zephyr/sys/timeutil.h>

Record a new instant in the time synchronization state.

Note that this updates only the latest persisted instant. The skew is not adjusted automatically.

Parameters

tsp	pointer to a timeutil_sync_state object.
inst	the new instant to be recorded. This becomes the base instant if there is no base instant, otherwise the value must be strictly after the base instant in both the reference and local time scales.

Return values

0	if installation succeeded in providing a new base
1	if installation provided a new latest instant
-EINVAL	if the new instant is not compatible with the base instant