[libcamera-devel] [PATCH 10/13] libcamera: raspberry: Report sensor timestamp

[Naushir Patuck]

Hi Jacopo,

Thank you for your work.

On Mon, 19 Apr 2021 at 14:14, Jacopo Mondi <jacopo at jmondi.org> wrote:

> Report the sensor's timestamp in the Request metadata by using the
> Unicam::Image buffer timestamp as an initial approximation.
>
> The buffer's timestamp is recorded at DMA-transfer time, and it does not
> theoretically matches the 'start of exposure' definition, but when used
> to compare two consecutive frames it gives an acceptable estimation of
> the sensor frame period duration.
>
> Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
> ---
>  src/libcamera/pipeline/raspberrypi/raspberrypi.cpp | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
> b/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
> index d1902bfc3393..7dc92acf3c4f 100644
> --- a/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
> +++ b/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
> @@ -1415,6 +1415,18 @@ void RPiCameraData::unicamBufferDequeue(FrameBuffer
> *buffer)
>                         << ", timestamp: " << buffer->metadata().timestamp;
>
>         if (stream == &unicam_[Unicam::Image]) {
> +               /*
> +                * Record the sensor timestamp in the Request.
> +                *
> +                * \todo The sensor timestamp should be better estimated by
> +                * sampling the V4L2Device::frameStart signal.
> +                */
>

Just a minor correction to this comment - the VB2 buffer timestamp that
is provided by the device driver is actually sampled at the CSI2 frame start
event, so is pretty much as close to the start of exposure as we can get
without dead reckoning.  This sample is also before the DMA to memory
and V4L2Device::frameStart signal.

Other than that,
Reviewed-by: Naushir Patuck <naush at raspberrypi.com>



> +               Request *request = requestQueue_.front();
> +               ASSERT(request);
> +
> +               request->metadata().set(controls::SensorTimestamp,
> +                                       buffer->metadata().timestamp);
> +
>                 /*
>                  * Lookup the sensor controls used for this frame sequence
> from
>                  * DelayedControl and queue them along with the frame
> buffer.
> --
> 2.31.1
>
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