[libcamera-devel] [PATCH 02/13] libcamera: ipu3: Report sensor timestamp

[Kieran Bingham]

Hi Jacopo,

On 19/04/2021 14:14, Jacopo Mondi wrote:
> Report the sensor's timestamp in the Request metadata by using the
> CIO2 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.
> 
> Reviewed-by: Hirokazu Honda <hiroh at chromium.org>
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
> ---
>  src/libcamera/pipeline/ipu3/ipu3.cpp | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/src/libcamera/pipeline/ipu3/ipu3.cpp b/src/libcamera/pipeline/ipu3/ipu3.cpp
> index 51446fcf5bc1..28e849a43a3e 100644
> --- a/src/libcamera/pipeline/ipu3/ipu3.cpp
> +++ b/src/libcamera/pipeline/ipu3/ipu3.cpp
> @@ -1255,6 +1255,15 @@ void IPU3CameraData::cio2BufferReady(FrameBuffer *buffer)
>  
>  	Request *request = info->request;
>  
> +	/*
> +	 * Record the sensor's timestamp in the request metadata.
> +	 *
> +	 * \todo The sensor timestamp should be better estimated by connecting
> +	 * to the V4L2Device::frameStart signal.

Shouldn't that be handled by the sensor driver itself then?

What defines the temporal location/point of the timestamp that is
returned currently?

I would have thought getting the time at the frameStart() signal would
be susceptible to more latency due to the signal handling and calling up
to userspace?

This must surely be something better handled by the kernel drivers right?


> +	 */
> +	request->metadata().set(controls::SensorTimestamp,
> +				buffer->metadata().timestamp);
> +
>  	/* If the buffer is cancelled force a complete of the whole request. */
>  	if (buffer->metadata().status == FrameMetadata::FrameCancelled) {
>  		for (auto it : request->buffers())
> 

-- 
Regards
--
Kieran