Re: [Libusb-devel] Howto process all pending events but be sure not to wait?

[Tim R. <ti...@pr...>]

Till Harbaum / Lists wrote:
> i am using libusb to write a video output driver for mplayer. Es expected, sometimes the USB is not fast enought to cope with the video rate.
>
> I am currently creating a transfer for every image to be sent. I set a flag at transfer submission and clear it in the callback. The problem now is: If i call the event handling until my flag is cleared, then i force mplayer to wait for every single usb transfer to complete. This is a problem if USB is too slow to play at full speed.
>
> I would like to process all pending events. If after that my flag still isn't cleared and know USB is too slow and i have to drop the frame. If it  is cleared i know i can send the next frame.
>
> How do i know whether there are still pending events to be handled?

You can do your USB work in a separate thread, and have it keep track of
the number of frames sent and completed.  If the difference becomes too
large, you can drop a frame.

Are you sending uncompressed data?  Are you using an isochronous pipe?

You should be able to figure out whether you'll drop data.  For
isochronous, you can push 24MB/s.  For bulk, you an push about 40MB/s.

-- 
Tim Roberts, ti...@pr...
Providenza & Boekelheide, Inc.