[libcamera-devel] [PATCH v11 1/3] libcamera: controls: Add frame duration control

[Laurent Pinchart]

Hi Naush,

Thank you for the patch.

On Wed, Jan 06, 2021 at 10:06:57AM +0000, Naushir Patuck wrote:
> Add an int64_t array control (controls::FrameDurations) to specify the
> minimum and maximum (in that order) frame duration to be used by the
> camera sensor.
> 
> Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
> Reviewed-by: David Plowman <david.plowman at raspberrypi.com>
> Tested-by: David Plowman <david.plowman at raspberrypi.com>
> Reviewed-by: Jacopo Mondi <jacopo at jmondi.org>
> ---
>  src/libcamera/control_ids.yaml | 38 ++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/src/libcamera/control_ids.yaml b/src/libcamera/control_ids.yaml
> index 6d6f0fee..d1240beb 100644
> --- a/src/libcamera/control_ids.yaml
> +++ b/src/libcamera/control_ids.yaml
> @@ -306,6 +306,44 @@ controls:
>          maximum valid value is given by the properties::ScalerCropMaximum
>          property, and the two can be used to implement digital zoom.
>  
> +  - FrameDurations:
> +      type: int64_t
> +      description: |
> +          The minimum and maximum (in that order) frame duration,
> +          expressed in micro-seconds.

s/micro-seconds/microseconds/

(The indentation should be 2 spaces btw)

> +
> +          When provided by applications, the control specifies the sensor frame
> +          duration interval the pipeline has to use. This limits the largest
> +          exposure time the sensor can use. For example, if a maximum frame
> +          duration of 33ms is requested (corresponding to 30 frames per second),
> +          the sensor will not be able to raise the exposure time above 33ms.
> +          A fixed frame duration is achieved by setting the minimum and maximum
> +          values to be the same. Setting both values to 0 reverts to using the
> +          IPA provided defaults.
> +
> +          The maximum frame duration provides the absolute limit to the shutter
> +          speed computed by the AE algorithm and it overrides any exposure mode
> +          setting specified with controls::AeExposureMode. Similarly, when a
> +          manual exposure time is set through controls::ExposureTime, it also
> +          gets clipped to the limits set by this control.

This looks good.

>            When reported in
> +          metadata, the control expresses the minimum and maximum frame
> +          durations used after being clipped to these limits.
> +

But this sounds weird. The previous part states that FrameDurations has
higher priority than all other parameters, but then this sentence says
it's clipped by "these limits".

> +          \sa AeExposureMode
> +          \sa ExposureTime
> +
> +          \todo Refer to the frame duration limits property to describe how
> +          application-provided values gets clipped and reset.

It hasn't been long, and the context is already starting to escape me.
Would it be possible to expand this just a little bit so that we'll know
what it means in 3 months time ?

> +
> +          \todo Define how to calculate the capture frame rate by
> +          defining controls to report additional delays introduced by
> +          the capture pipeline or post-processing stages (ie JPEG
> +          conversion, frame scaling).
> +
> +          \todo Provide an explicit definition of default control values, for
> +          this and all other controls.
> +      size: [2]
> +
>    # ----------------------------------------------------------------------------
>    # Draft controls section
>  

-- 
Regards,

Laurent Pinchart