On Sat, 27 Oct 2012, Stefan May wrote:
> Dear Alan,
>
> maybe there is a bug in VMWare. If so, there must be either a bug in the
> firmware or in the uvc module, since the camera is not working on native
> Linux without the nodrop option.
>
> I verified the following. In uvc_video.c at line 595
>
> if (urb->iso_frame_desc[i].status < 0) {
> uvc_trace(UVC_TRACE_FRAME, "USB isochronous frame "
> "lost (%d).\n", urb->iso_frame_desc[i].status);
> /* Mark the buffer as faulty. */
> if (buf != NULL)
> buf->error = 1;
> continue;
> }
>
> a complete URB is dropped, if one of the packets is erroneous. The
> format is uncompressed in my case. The comparison at line 627
> buf->buf.length != buf->buf.bytesused
> will set
> buf->error = 1;
> for almost every URB.
I'm not an expert on the uvcvideo driver. You should ask that driver's
maintainer about this.
> I added one line after above mentioned block for testing purposes:
>
> if (urb->iso_frame_desc[i].status < 0) {
> uvc_trace(UVC_TRACE_FRAME, "USB isochronous frame "
> "lost (%d).\n", urb->iso_frame_desc[i].status);
> /* Mark the buffer as faulty. */
> if (buf != NULL)
> buf->error = 1;
> continue;
> }
> buf->error = 0;
>
> resetting buf->error in order to receive at least the remaining packets
> with no status flag < 0.
> So, I just discard erroneous packets, not the whole URB.
> Loading uvcvideo with this modification provides a data stream as
> expected, even without the nodrop option. The syslog trace now looks
> like below. You can see that for every URB three isochronous frames are
> lost, and 29 packets are received. Are you sure that this is not a
> firmware problem?
Let's try to be precise.
The fact that three frames out of 32 get dropped may well be caused by
a firmware bug in your camera. But that's not what I was talking about
(and as far as I can tell, it's not what you asked about in the first
messages you posted on this topic).
The fact that VMWare changes the status codes from -71 to 0 has nothing
to do with the firmware. It is a bug in VMWare. This was your
original question; you asked why the camera worked without errors in
the guest but not in the host.
Alan Stern
--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
