[pwc] Lots of underflow messages with hub/extension cable

["Carlo E. Prelz" <>]

Hallo there. I have been successfully using a Logitech camera. The
camera is identified as Logitech QuickCam 4000 Pro USB webcam.

The normal messages I receive are as follows:

Sep 19 11:36:37 interactor kernel: pwc Logitech QuickCam 4000 Pro USB webcam 
detected.
Sep 19 11:36:37 interactor kernel: pwc Registered as /dev/video0.
Sep 19 11:37:09 interactor kernel: pwc Failed to set LED on/off time.
Sep 19 11:37:09 interactor kernel: pwc type = 740
Sep 19 11:37:09 interactor kernel: pwc type = 740
Sep 19 11:37:09 interactor kernel: pwc set_video_mode(640x480 @ 9, palette 15).
Sep 19 11:37:09 interactor kernel: pwc decode_size = 5.
Sep 19 11:37:09 interactor kernel: pwc Using alternate setting 6.
Sep 19 11:37:09 interactor kernel: pwc set_video_mode(320x240 @ 9, palette 15).
Sep 19 11:37:09 interactor kernel: pwc decode_size = 3.

...
...

and at the end of the application: 

Sep 19 11:37:29 interactor kernel: pwc Closing video device: 90 frames 
received, dumped 0 frames, 0 frames with errors.

If I connect the camera via a USB2.0 active extension cable (ATEN
UE-250) or a powered 2.0 4-port hub (Trust Item No. 13119), or both, I
am submerged by buffer underflow messages:

Sep 19 11:35:35 interactor kernel: pwc Logitech QuickCam 4000 Pro USB webcam 
detected.
Sep 19 11:35:35 interactor kernel: pwc Registered as /dev/video0.
Sep 19 11:36:04 interactor kernel: pwc Failed to set LED on/off time.
Sep 19 11:36:04 interactor kernel: pwc type = 740
Sep 19 11:36:04 interactor kernel: pwc type = 740
Sep 19 11:36:04 interactor kernel: pwc set_video_mode(640x480 @ 9, palette 15).
Sep 19 11:36:04 interactor kernel: pwc decode_size = 5.
Sep 19 11:36:04 interactor kernel: pwc Using alternate setting 6.
Sep 19 11:36:05 interactor kernel: pwc set_video_mode(320x240 @ 9, palette 15).
Sep 19 11:36:05 interactor kernel: pwc decode_size = 3.
Sep 19 11:36:05 interactor kernel: pwc Using alternate setting 4.
Sep 19 11:36:06 interactor kernel: pwc Frame buffer underflow (447 bytes); 
discarded.
Sep 19 11:36:06 interactor kernel: pwc Frame buffer underflow (668 bytes); 
discarded.
...

and so forth, at the rate of 3 or 4 screenfuls a second. No frame can
be captured.

Is maybe there any sensitive tuning to make on the driver? I am using
kernel 2.6.12.6 on an Athlon64-based machine, based on the ATI
Xpress200 chipset. The application is self-developed, using a simple
V4l interface. More details on request.

Thanks in advance

Carlo - Den Haag, the Netherlands

-- 
  *         Se la Strada e la sua Virtu' non fossero state messe da parte,
* K * Carlo E. Prelz -              che bisogno ci sarebbe
  *               di parlare tanto di amore e di rettitudine? (Chuang-Tzu)
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