Re: How should we handle isochronous underruns?

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On Mon, 1 Jul 2013, Laurent Pinchart wrote:

> That's correct. Unlike the UAC driver, the UVC driver doesn't care too much 
> about exact timings. Avoiding packet loss is my main concern. As video frames 
> are not delivered to userspace before they are fully transmitted, and given 
> the large number of URBs required to transmit a video frame, I can submit more 
> URBs (without reasonable limits) if that can help avoiding underruns.

> A couple of users have experienced underruns in the past due to a rogue driver 
> disabling interrupts for tens of milliseconds. I don't think switching to 
> tasklets will have a strong adverse effect, the 20ms buffer time should be 
> large enough to avoid underruns in sane systems.

What about error recovery for insane systems?  If we do get a 50-ms gap
in the data stream, what's the best way for the UVC driver to learn
this has happens and attempt to carry on?

Alan Stern

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