clock_recovery.h

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/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * Copyright (C) 2024, Raspberry Pi Ltd
 *
 * Camera recovery algorithm
 */
#pragma once
 
#include <stdint.h>
 
namespace libcamera {
 
class ClockRecovery
{
public:
    ClockRecovery();
 
    void configure(unsigned int numSamples = 100, unsigned int maxJitter = 2000,
               unsigned int minSamples = 10, unsigned int errorThreshold = 50000);
    void reset();
 
    void addSample();
    void addSample(uint64_t input, uint64_t output);
 
    uint64_t getOutput(uint64_t input);
 
private:
    /* Approximate number of samples over which the model state persists. */
    unsigned int numSamples_;
    /* Remove any output jitter larger than this immediately. */
    unsigned int maxJitter_;
    /* Number of samples required before we start to use model estimates. */
    unsigned int minSamples_;
    /* Threshold above which we assume the wallclock has been reset. */
    unsigned int errorThreshold_;
 
    /* How many samples seen (up to numSamples_). */
    unsigned int count_;
    /* This gets subtracted from all input values, just to make the numbers easier. */
    uint64_t inputBase_;
    /* As above, for the output. */
    uint64_t outputBase_;
    /* The previous input sample. */
    uint64_t lastInput_;
    /* The previous output sample. */
    uint64_t lastOutput_;
 
    /* Average x value seen so far. */
    double xAve_;
    /* Average y value seen so far */
    double yAve_;
    /* Average x^2 value seen so far. */
    double x2Ave_;
    /* Average x*y value seen so far. */
    double xyAve_;
 
    /*
     * The latest estimate of linear parameters to derive the output clock
     * from the input.
     */
    double slope_;
    double offset_;
 
    /* Use this cumulative error to monitor for spontaneous clock updates. */
    double error_;
};
 
} /* namespace libcamera */