Re: A videocam works on OHCI and fails on UHCI (fwd)

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Theodore Kilgore wrote:


On Sat, 14 Nov 2009, Oliver Neukum wrote:

Am Samstag, 14. November 2009 04:35:55 schrieb Theodore Kilgore:
At this point, I have put identical copies of the camera driver, along
with identical copies of the rest of the gspca development tree, on six different machines. Three of them use OHCI, and three of them use UHCI. On
 the three machines which use OHCI, everything works perfectly. On the
three machines which run UHCI, there are serious problems, to the extent
 that some of the cameras I have intended to support will not function
 while others do continue to work.

This sounds very much like a problem I had when developing the stv680 camera driver. I had ohci hardware and the camera worked well, but I kept getting reports that others where having problems- the video output (as seen in an application, e.g., xawtv) would be very jumpy and even freeze up. It wasn't until I got a computer with uhci hardware that I started having the same problem. One of the camera users sent me a patch for the (then) uhci code. This was back in the 2.4 or early 2.6 kernel days. The patch was simply to change a parameter in the uhci code. With this patch, the camera worked as well as with ohci. I believe that at the time there were several uhci drivers, or usb core, or something, and when they were consolidated, the patch was lost. Currently (I am now using 2.6.29.7), when connected to uhci hardware the camera has problems as before, but still works as expected with ohci. I will have to dig through my hard copies of the stv680 driver development to find out what version of uhci had this problem and exactly what the fix was, but the code has changed so much since then that the information may not be useful.

Kevin
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