From patchwork Thu Jun 19 10:05:54 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Naushir Patuck X-Patchwork-Id: 23603 Return-Path: X-Original-To: parsemail@patchwork.libcamera.org Delivered-To: parsemail@patchwork.libcamera.org Received: from lancelot.ideasonboard.com (lancelot.ideasonboard.com [92.243.16.209]) by patchwork.libcamera.org (Postfix) with ESMTPS id 50C4BC3237 for ; Thu, 19 Jun 2025 10:09:10 +0000 (UTC) Received: from lancelot.ideasonboard.com (localhost [IPv6:::1]) by lancelot.ideasonboard.com (Postfix) with ESMTP id C0BE268DC6; Thu, 19 Jun 2025 12:09:06 +0200 (CEST) Authentication-Results: lancelot.ideasonboard.com; dkim=pass (2048-bit key; unprotected) header.d=raspberrypi.com header.i=@raspberrypi.com header.b="LK4yHjBY"; dkim-atps=neutral Received: from mail-wm1-x32e.google.com (mail-wm1-x32e.google.com [IPv6:2a00:1450:4864:20::32e]) by lancelot.ideasonboard.com (Postfix) with ESMTPS id EDB5968DC6 for ; Thu, 19 Jun 2025 12:09:02 +0200 (CEST) Received: by mail-wm1-x32e.google.com with SMTP id 5b1f17b1804b1-450ddb35583so534915e9.1 for ; Thu, 19 Jun 2025 03:09:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=raspberrypi.com; s=google; t=1750327742; x=1750932542; darn=lists.libcamera.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=LpSvAHfLJ3s+U22kjYDMqV0WiShYD8LM29GMSrXDETg=; b=LK4yHjBYtNdg/2i6fv2SpyBcjtb0j7HXculovw3BAYYwqG6EL81YK/EPHdAwRgfRmT sxQWExxde7O1iVGaBJbuqwhrkJoWLK5+MjiiWUfcjlD7iOZdsJQjV2JvY8rCX4wlfmJd C9FS2aGFiIH5l/DMBd42/IfBxeHUeat4bUbx35PRkbu1JEjnzz2f3+dNbcrSLBnhnYBE 4SFzct4B7iAMo/4rbeR/Vlyq5TNTu+dsuJPn9LnoDN/q0fyvGSIaRs/c/SuKka1wq86W ClEpWzI05tjKQBEu3/ioKNnB8XbIN5p1pwbMoeyZX8t5bfBQFQxRkmXPCGh+wZ/Qjr1c /R1A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1750327742; x=1750932542; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=LpSvAHfLJ3s+U22kjYDMqV0WiShYD8LM29GMSrXDETg=; b=CSl4cODw4p9V8plpobQLMfER1Gqw0o9k2h5Ly9GqQquNNasTUGFpvaeYppSFv5zYvZ cZ/mwbQu9F3X/svrWeNOCP8BT3D1REy8vFJQRMijQ+Rn64QGA+yvThQEyTZ54NA/zQFE UpXBZTDpD5j6ZWK1G/CTZaIvnzfpuVPnQhUCIDHkMH3VkWn9MvLxQVPmXNOo7NJ05tMs Vxc+N6RE3en5h22vUm1j9+6C5pKb76rkCvkLZJd8KFc/vHaRa3jSe5nSnsT82IiEjNfx I/SaDvhV9QnUkQjleIXHKPFr/NPH7iofJOKnA8TnhweniUZx1nggbSpwId5wt/EJiuRV mX0g== X-Gm-Message-State: AOJu0YxWl8GU95Q73k0B1Z0nDVT2FUjvVE8m2CyLFP6Skxv+0OM/3czT 6GGrxLxdGR/5xrf5AgXjnmxwGgxzpjMAQ8FKsjSH0vTPfg073+dLwqQnZ82Nyq40nmxSnnPUqlV bASDE X-Gm-Gg: ASbGnctuxPIvnF4pmj+i92cq3duovRLd03Nu+1GtPtPVj1LZcvCQAhsqgTezDvQKC5q mtaKwaPiw+fqXUIOFgs6zGFGjCg0KBHCiqNgBu08YWxuBwozBwBpzZ4YrxgB2RjJtM8AR86OL6c O78wVAo1VKY4QVZ209Nc2rD/itCFthjBV1Jp39ukQxuOKJ4g2L24uaj/lhe0FeLeGGLE4WFswSE /0mPM5JbYjZv0nkvyGV3z5mfhoC6PeAUw/3nKHOe99Cj5kH+gCOaO7+AFhvs2dBLvi+6K3cD/s9 qzh4sIRsKAI4Ytk9rqK06hp5KE4q5sFlBnv/yYCbBcBh8V3GJYhdMmfuxy2GwzhTrORYkosduWX Qxyek/Q== X-Google-Smtp-Source: AGHT+IHFlnDKgmvT9vjneCyg/TA3DOrvI/cwCPwmA+rGb91gd97oMReSGqXRRcxCre5RqlilBEWiRA== X-Received: by 2002:a05:600c:a402:b0:451:dee4:cd07 with SMTP id 5b1f17b1804b1-4535eee3c98mr7918565e9.0.1750327742109; Thu, 19 Jun 2025 03:09:02 -0700 (PDT) Received: from NAUSH-P-DELL.pitowers.org ([93.93.133.154]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4535ebcecb5sm23926555e9.37.2025.06.19.03.09.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Jun 2025 03:09:01 -0700 (PDT) From: Naushir Patuck To: libcamera-devel@lists.libcamera.org Cc: kieran.bingham@ideasonboard.com, David Plowman , Naushir Patuck Subject: [PATCH 2/4] libcamera: Add ClockRecovery class to generate wallclock timestamps Date: Thu, 19 Jun 2025 11:05:54 +0100 Message-ID: <20250619100857.124809-3-naush@raspberrypi.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250619100857.124809-1-naush@raspberrypi.com> References: <20250619100857.124809-1-naush@raspberrypi.com> MIME-Version: 1.0 X-BeenThere: libcamera-devel@lists.libcamera.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: libcamera-devel-bounces@lists.libcamera.org Sender: "libcamera-devel" From: David Plowman The ClockRecovery class takes pairs of timestamps from two different clocks, and models the second ("output") clock from the first ("input") clock. We can use it, in particular, to get a good wallclock estimate for a frame's SensorTimestamp. Signed-off-by: David Plowman Reviewed-by: Kieran Bingham Reviewed-by: Naushir Patuck Signed-off-by: Naushir Patuck --- include/libcamera/internal/clock_recovery.h | 68 ++++++ include/libcamera/internal/meson.build | 1 + src/libcamera/clock_recovery.cpp | 230 ++++++++++++++++++++ src/libcamera/meson.build | 1 + 4 files changed, 300 insertions(+) create mode 100644 include/libcamera/internal/clock_recovery.h create mode 100644 src/libcamera/clock_recovery.cpp diff --git a/include/libcamera/internal/clock_recovery.h b/include/libcamera/internal/clock_recovery.h new file mode 100644 index 000000000000..43e46b7dcf9f --- /dev/null +++ b/include/libcamera/internal/clock_recovery.h @@ -0,0 +1,68 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ +/* + * Copyright (C) 2024, Raspberry Pi Ltd + * + * Camera recovery algorithm + */ +#pragma once + +#include + +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 */ diff --git a/include/libcamera/internal/meson.build b/include/libcamera/internal/meson.build index 33f318b2b602..5c80a28c4cbe 100644 --- a/include/libcamera/internal/meson.build +++ b/include/libcamera/internal/meson.build @@ -11,6 +11,7 @@ libcamera_internal_headers = files([ 'camera_manager.h', 'camera_sensor.h', 'camera_sensor_properties.h', + 'clock_recovery.h', 'control_serializer.h', 'control_validator.h', 'converter.h', diff --git a/src/libcamera/clock_recovery.cpp b/src/libcamera/clock_recovery.cpp new file mode 100644 index 000000000000..abacf444fbf8 --- /dev/null +++ b/src/libcamera/clock_recovery.cpp @@ -0,0 +1,230 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ +/* + * Copyright (C) 2024, Raspberry Pi Ltd + * + * Clock recovery algorithm + */ + +#include "libcamera/internal/clock_recovery.h" + +#include + +#include + +/** + * \file clock_recovery.h + * \brief Clock recovery - deriving one clock from another independent clock + */ + +namespace libcamera { + +LOG_DEFINE_CATEGORY(ClockRec) + +/** + * \class ClockRecovery + * \brief Recover an output clock from an input clock + * + * The ClockRecovery class derives an output clock from an input clock, + * modelling the output clock as being linearly related to the input clock. + * For example, we may use it to derive wall clock timestamps from timestamps + * measured by the internal system clock which counts local time since boot. + * + * When pairs of corresponding input and output timestamps are available, + * they should be submitted to the model with addSample(). The model will + * update, and output clock values for known input clock values can be + * obtained using getOutput(). + * + * As a convenience, if the input clock is indeed the time since boot, and the + * output clock represents a real wallclock time, then addSample() can be + * called with no arguments, and a pair of timestamps will be captured at + * that moment. + * + * The configure() function accepts some configuration parameters to control + * the linear fitting process. + */ + +/** + * \brief Construct a ClockRecovery + */ +ClockRecovery::ClockRecovery() +{ + configure(); + reset(); +} + +/** + * \brief Set configuration parameters + * \param[in] numSamples The approximate duration for which the state of the model + * is persistent + * \param[in] maxJitter New output samples are clamped to no more than this + * amount of jitter, to prevent sudden swings from having a large effect + * \param[in] minSamples The fitted clock model is not used to generate outputs + * until this many samples have been received + * \param[in] errorThreshold If the accumulated differences between input and + * output clocks reaches this amount over a few frames, the model is reset + */ +void ClockRecovery::configure(unsigned int numSamples, unsigned int maxJitter, + unsigned int minSamples, unsigned int errorThreshold) +{ + LOG(ClockRec, Debug) + << "configure " << numSamples << " " << maxJitter << " " << minSamples << " " << errorThreshold; + + numSamples_ = numSamples; + maxJitter_ = maxJitter; + minSamples_ = minSamples; + errorThreshold_ = errorThreshold; +} + +/** + * \brief Reset the clock recovery model and start again from scratch + */ +void ClockRecovery::reset() +{ + LOG(ClockRec, Debug) << "reset"; + + lastInput_ = 0; + lastOutput_ = 0; + xAve_ = 0; + yAve_ = 0; + x2Ave_ = 0; + xyAve_ = 0; + count_ = 0; + error_ = 0.0; + /* + * Setting slope_ and offset_ to zero initially means that the clocks + * advance at exactly the same rate. + */ + slope_ = 0.0; + offset_ = 0.0; +} + +/** + * \brief Add a sample point to the clock recovery model, for recovering a wall + * clock value from the internal system time since boot + * + * This is a convenience function to make it easy to derive a wall clock value + * (using the Linux CLOCK_REALTIME) from the time since the system started + * (measured by CLOCK_BOOTTIME). + */ +void ClockRecovery::addSample() +{ + LOG(ClockRec, Debug) << "addSample"; + + struct timespec bootTime1; + struct timespec bootTime2; + struct timespec wallTime; + + /* Get boot and wall clocks in microseconds. */ + clock_gettime(CLOCK_BOOTTIME, &bootTime1); + clock_gettime(CLOCK_REALTIME, &wallTime); + clock_gettime(CLOCK_BOOTTIME, &bootTime2); + uint64_t boot1 = bootTime1.tv_sec * 1000000ULL + bootTime1.tv_nsec / 1000; + uint64_t boot2 = bootTime2.tv_sec * 1000000ULL + bootTime2.tv_nsec / 1000; + uint64_t boot = (boot1 + boot2) / 2; + uint64_t wall = wallTime.tv_sec * 1000000ULL + wallTime.tv_nsec / 1000; + + addSample(boot, wall); +} + +/** + * \brief Add a sample point to the clock recovery model, specifying the exact + * input and output clock values + * \param[in] input The input clock value + * \param[in] output The value of the output clock at the same moment, as far + * as possible, that the input clock was sampled + * + * This function should be used for corresponding clocks other than the Linux + * BOOTTIME and REALTIME clocks. + */ +void ClockRecovery::addSample(uint64_t input, uint64_t output) +{ + LOG(ClockRec, Debug) << "addSample " << input << " " << output; + + if (count_ == 0) { + inputBase_ = input; + outputBase_ = output; + } + + /* + * We keep an eye on cumulative drift over the last several frames. If this exceeds a + * threshold, then probably the system clock has been updated and we're going to have to + * reset everything and start over. + */ + if (lastOutput_) { + int64_t inputDiff = getOutput(input) - getOutput(lastInput_); + int64_t outputDiff = output - lastOutput_; + error_ = error_ * 0.95 + (outputDiff - inputDiff); + if (std::abs(error_) > errorThreshold_) { + reset(); + inputBase_ = input; + outputBase_ = output; + } + } + lastInput_ = input; + lastOutput_ = output; + + /* + * Never let the new output value be more than maxJitter_ away from what + * we would have expected. This is just to reduce the effect of sudden + * large delays in the measured output. + */ + uint64_t expectedOutput = getOutput(input); + output = std::clamp(output, expectedOutput - maxJitter_, expectedOutput + maxJitter_); + + /* + * We use x, y, x^2 and x*y sums to calculate the best fit line. Here we + * update them by pretending we have count_ samples at the previous fit, + * and now one new one. Gradually the effect of the older values gets + * lost. This is a very simple way of updating the fit (there are much + * more complicated ones!), but it works well enough. Using averages + * instead of sums makes the relative effect of old values and the new + * sample clearer. + */ + double x = static_cast(input - inputBase_); + double y = static_cast(output - outputBase_) - x; + unsigned int count1 = count_ + 1; + xAve_ = (count_ * xAve_ + x) / count1; + yAve_ = (count_ * yAve_ + y) / count1; + x2Ave_ = (count_ * x2Ave_ + x * x) / count1; + xyAve_ = (count_ * xyAve_ + x * y) / count1; + + /* + * Don't update slope and offset until we've seen "enough" sample + * points. Note that the initial settings for slope_ and offset_ + * ensures that the wallclock advances at the same rate as the realtime + * clock (but with their respective initial offsets). + */ + if (count_ > minSamples_) { + /* These are the standard equations for least squares linear regression. */ + slope_ = (count1 * count1 * xyAve_ - count1 * xAve_ * count1 * yAve_) / + (count1 * count1 * x2Ave_ - count1 * xAve_ * count1 * xAve_); + offset_ = yAve_ - slope_ * xAve_; + } + + /* + * Don't increase count_ above numSamples_, as this controls the long-term + * amount of the residual fit. + */ + if (count1 < numSamples_) + count_++; +} + +/** + * \brief Calculate the output clock value according to the model from an input + * clock value + * \param[in] input The input clock value + * + * \return Output clock value + */ +uint64_t ClockRecovery::getOutput(uint64_t input) +{ + double x = static_cast(input - inputBase_); + double y = slope_ * x + offset_; + uint64_t output = y + x + outputBase_; + + LOG(ClockRec, Debug) << "getOutput " << input << " " << output; + + return output; +} + +} /* namespace libcamera */ diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build index 202db1efe844..28a3b0f36d53 100644 --- a/src/libcamera/meson.build +++ b/src/libcamera/meson.build @@ -21,6 +21,7 @@ libcamera_internal_sources = files([ 'byte_stream_buffer.cpp', 'camera_controls.cpp', 'camera_lens.cpp', + 'clock_recovery.cpp', 'control_serializer.cpp', 'control_validator.cpp', 'converter.cpp',