Hi Brian,
On Saturday 22 December 2007, Brian Pin wrote:
> In uvc_video.c:
>
> uvc_init_video_isoc(...) {
>
> npackets = (size + psize - 1) / psize;
> if (npackets > UVC_MAX_ISO_PACKETS)
> npackets = UVC_MAX_ISO_PACKETS;
>
> }
> in mycase I originally have npackets = 199, and after the 3 lines there, it
> becomes 40, which is UVC_MAX_ISO_PACKETS.
> My question is if there is a frame that needs more than 40 packets to
> transfer, how is the data going to be not lost?
> Is it because we send multiple URBs (I set UVC_URBS to 1)?
The driver resubmits URBs after they complete. Even with a small number of
packets and a small number of URBs, if the device is able to buffer enough
data and if the host is fast enough to resubmit, data won't be lost.
In practice the number of packets and the number of URBs is a compromise
between the memory footprint and the ability to handle delays in URB
resubmission.
Best regards,
Laurent Pinchart
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