Re: [RFC v4] V4L2 API for flash devices

[Mauro Carvalho Chehab <mchehab@redhat.com>]

Em 19-05-2011 05:12, Sakari Ailus escreveu:
> Sylwester Nawrocki wrote:

>>>> These were mostly fixed point arithmetic numbers in [32-bit numerator/
>>>> 32-bit denominator] form carrying exposure time, shutter speed, aperture,
>>>> brightness, flash, etc. information. The tags could be read from ISP after
>>>> it buffered a frame in its memory and processed it.
>>>> In case of a JPEG image format the tags can be embedded into the main
>>>> image file. But the image processors not always supported that so we used
>>>> to have an ioctl for the purpose of retrieving the metadata in user space.
>>>> In some cases it is desired to read data directly from the driver rather
>>>> than parsing a relatively large buffer.
>>>> It would be good to have a uniform interface for passing such data to
>>>> applications. I think in that particular use case a control id/value pair
>>>> sequences would do.
 
> - Which formats are your rational numbers in? A kernel interface can't
> really have floating point numbers, so there would need to be a sane way
> to pass these to user space.

The V4L2 API has support for rational numbers. The frame rate is specified as a
rational number. There's a struct for that:

struct v4l2_fract {
	__u32   numerator;
	__u32   denominator;
};

Cheers,
Mauro