[PATCH v2 2/3] ipa: raspberrypi: Better heruistics for calculating Unicam timeout

[Naushir Patuck]

The existing mechanism of setting a timeout value simply uses the
maximum possible frame length advertised by the sensor mode. This can be
problematic when, for example, the IMX477 sensor can use a frame length
of over 600 seconds. However, for typical usage the frame length will
never go over several 100s of milliseconds, making the timeout very
impractical.

Store a list of the last 10 frame length values requested by the AGC. On
startup, and at the end of every frame, take the maximum frame length
value from this list and return that to the pipeline handler through the
setCameraTimeoutValue() signal. This allows the timeout value to better
track the actual sensor usage.

Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
Reviewed-by: David Plowman <david.plowman at raspberrypi.com>
---
 src/ipa/raspberrypi/raspberrypi.cpp | 44 +++++++++++++++++++++++++++--
 1 file changed, 41 insertions(+), 3 deletions(-)

diff --git a/src/ipa/raspberrypi/raspberrypi.cpp b/src/ipa/raspberrypi/raspberrypi.cpp
index f6826bf27fe1..7b5aed644a67 100644
--- a/src/ipa/raspberrypi/raspberrypi.cpp
+++ b/src/ipa/raspberrypi/raspberrypi.cpp
@@ -8,6 +8,7 @@
 #include <algorithm>
 #include <array>
 #include <cstring>
+#include <deque>
 #include <fcntl.h>
 #include <math.h>
 #include <stdint.h>
@@ -64,6 +65,9 @@ using utils::Duration;
 /* Number of metadata objects available in the context list. */
 constexpr unsigned int numMetadataContexts = 16;
 
+/* Number of frame length times to hold in the queue. */
+constexpr unsigned int FrameLengthsQueueSize = 10;
+
 /* Configure the sensor with these values initially. */
 constexpr double defaultAnalogueGain = 1.0;
 constexpr Duration defaultExposureTime = 20.0ms;
@@ -121,7 +125,8 @@ class IPARPi : public IPARPiInterface
 public:
 	IPARPi()
 		: controller_(), frameCount_(0), checkCount_(0), mistrustCount_(0),
-		  lastRunTimestamp_(0), lsTable_(nullptr), firstStart_(true)
+		  lastRunTimestamp_(0), lsTable_(nullptr), firstStart_(true),
+		  lastTimeout_(0s)
 	{
 	}
 
@@ -155,6 +160,7 @@ private:
 	void fillDeviceStatus(const ControlList &sensorControls, unsigned int ipaContext);
 	RPiController::StatisticsPtr fillStatistics(bcm2835_isp_stats *stats) const;
 	void processStats(unsigned int bufferId, unsigned int ipaContext);
+	void setCameraTimeoutValue();
 	void applyFrameDurations(Duration minFrameDuration, Duration maxFrameDuration);
 	void applyAGC(const struct AgcStatus *agcStatus, ControlList &ctrls);
 	void applyAWB(const struct AwbStatus *awbStatus, ControlList &ctrls);
@@ -220,6 +226,10 @@ private:
 
 	/* Maximum gain code for the sensor. */
 	uint32_t maxSensorGainCode_;
+
+	/* Track the frame length times over FrameLengthsQueueSize frames. */
+	std::deque<Duration> frameLengths_;
+	Duration lastTimeout_;
 };
 
 int IPARPi::init(const IPASettings &settings, bool lensPresent, IPAInitResult *result)
@@ -284,6 +294,10 @@ void IPARPi::start(const ControlList &controls, StartConfig *startConfig)
 
 	controller_.switchMode(mode_, &metadata);
 
+	/* Reset the frame lengths queue */
+	frameLengths_.clear();
+	frameLengths_.resize(FrameLengthsQueueSize, 0s);
+
 	/* SwitchMode may supply updated exposure/gain values to use. */
 	AgcStatus agcStatus;
 	agcStatus.shutterTime = 0.0s;
@@ -294,6 +308,7 @@ void IPARPi::start(const ControlList &controls, StartConfig *startConfig)
 		ControlList ctrls(sensorCtrls_);
 		applyAGC(&agcStatus, ctrls);
 		startConfig->controls = std::move(ctrls);
+		setCameraTimeoutValue();
 	}
 
 	/*
@@ -340,8 +355,6 @@ void IPARPi::start(const ControlList &controls, StartConfig *startConfig)
 	}
 
 	startConfig->dropFrameCount = dropFrameCount_;
-	const Duration maxSensorFrameDuration = mode_.maxFrameLength * mode_.maxLineLength;
-	setCameraTimeout.emit(maxSensorFrameDuration.get<std::milli>());
 
 	firstStart_ = false;
 	lastRunTimestamp_ = 0;
@@ -1434,6 +1447,22 @@ void IPARPi::processStats(unsigned int bufferId, unsigned int ipaContext)
 		applyAGC(&agcStatus, ctrls);
 
 		setDelayedControls.emit(ctrls, ipaContext);
+		setCameraTimeoutValue();
+	}
+}
+
+void IPARPi::setCameraTimeoutValue()
+{
+	/*
+	 * Take the maximum value of the exposure queue as the camera timeout
+	 * value to pass back to the pipeline handler. Only signal if it has changed
+	 * from the last set value.
+	 */
+	auto max = std::max_element(frameLengths_.begin(), frameLengths_.end());
+
+	if (*max != lastTimeout_) {
+		setCameraTimeout.emit(max->get<std::milli>());
+		lastTimeout_ = *max;
 	}
 }
 
@@ -1522,6 +1551,15 @@ void IPARPi::applyAGC(const struct AgcStatus *agcStatus, ControlList &ctrls)
 	 */
 	if (mode_.minLineLength != mode_.maxLineLength)
 		ctrls.set(V4L2_CID_HBLANK, static_cast<int32_t>(hblank));
+
+	/*
+	 * Store the frame length times in a circular queue, up-to FrameLengthsQueueSize
+	 * elements. This will be used to advertise a camera timeout value to the
+	 * pipeline handler.
+	 */
+	frameLengths_.pop_front();
+	frameLengths_.push_back(helper_->exposure(vblank + mode_.height,
+						  helper_->hblankToLineLength(hblank)));
 }
 
 void IPARPi::applyDG(const struct AgcStatus *dgStatus, ControlList &ctrls)
-- 
2.34.1