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51 lines
1.6 KiB
C
51 lines
1.6 KiB
C
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// Copyright 2022, Collabora, Ltd.
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// SPDX-License-Identifier: BSL-1.0
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/*!
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* @file
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* @brief Helpers to estimate offsets between clocks
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* @author Mateo de Mayo <mateo.demayo@collabora.com>
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* @ingroup aux_math
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*/
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#pragma once
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#include "util/u_time.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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/*!
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* Helper to estimate the offset between two clocks using exponential smoothing.
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*
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* Given a sample from two timestamp domains A and B that should have been
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* sampled as close as possible, together with an estimate of the offset between
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* A clock and B clock (or zero), it applies a smoothing average on the
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* estimated offset and returns @p a in B clock.
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*
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* @param freq About how many times per second this function is called. Helps setting a good decay value.
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* @param a Timestamp in clock A of the event
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* @param b Timestamp in clock B of the event
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* @param[in,out] inout_a2b Pointer to the current offset estimate from A to B, or 0 if unknown.
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* Value pointed-to will be updated.
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* @return timepoint_ns @p a in B clock
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*/
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static inline timepoint_ns
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m_clock_offset_a2b(float freq, timepoint_ns a, timepoint_ns b, time_duration_ns *inout_a2b)
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{
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// Totally arbitrary way of computing alpha, if you have a better one, replace it
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const float alpha = 1.0 - 12.5 / freq; // Weight to put on accumulated a2b
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time_duration_ns old_a2b = *inout_a2b;
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time_duration_ns got_a2b = b - a;
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time_duration_ns new_a2b = old_a2b * alpha + got_a2b * (1.0 - alpha);
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if (old_a2b == 0) { // a2b has not been set yet
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new_a2b = got_a2b;
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}
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*inout_a2b = new_a2b;
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return a + new_a2b;
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}
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#ifdef __cplusplus
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}
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#endif
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