Hi Laurent,
On Thu, 9 Nov 2017, Laurent Pinchart wrote:
> Hi Guennadi,
>
> On Wednesday, 8 November 2017 12:43:46 EET Guennadi Liakhovetski wrote:
[snip]
> > To recall the metadata buffer layout should be
> >
> > struct uvc_meta_buf {
> > uint64_t ns;
> > uint16_t sof;
> > uint8_t length;
> > uint8_t flags;
> > uint8_t buf[];
> > } __attribute__((packed));
> >
> > where all the fields, beginning with "length" are a direct copy from the
> > UVC payload header. If multiple such payload headers have arrived for a
> > single frame, they will be appended and .bytesused will as usually have
> > the total byte count, used up in this frame. An application would then
> > calculate lengths of those individual metadata blocks as
> >
> > sizeof(.ns) + sizeof(.sof) + .length
> >
> > But this won't work with the "standard" UVC metadata format where any
> > private data, following standard fields, are dropped. In that case
> > applications would have to look at .flags and calculate the block length
> > based on them. Another possibility would be to rewrite the .length field
> > in the driver to only include standard fields, but I really don't think
> > that would be a good idea.
>
> For the standard header the length can indeed be easily computed from the
> flags. I wonder, however, why you think rewriting length would be a bad idea ?
Because I like the guarantee of the least intrusion. We (so far)
guarantee, that the buffer contents beyond the system and the USB
timestamps are a direct unmodified copy from the camera. This seems to be
a good principle to stick to.
Thanks
Guennadi
