[linux-uvc-devel] Patch: add bandwidth limit for compressed format

[Sven-Ola Tuecke]

Hey,

want to operate three webcams. With MJPEG compression on, ***@30 it
should be possible to use at least 2 of them at the same USB bus, but
obviously nobody wants to calculate the compression-to-bandwidth
estimation (neither driver nor OEM). Here's a hack, that seems to work
fine. Please comment.

// Sven-Ola

[stuart]

Hi Sven,

Reik Red and I did quite a bit of work on this about 3 months ago and
have had no interest on this forum:

http://superuser.com/questions/431759/using-multiple-usb-webcams-in-linux/1018342#1018342

or from anyone on this mailing list where the specific thread starts here:

https://sourceforge.net/p/linux-uvc/mailman/message/34748762/

In addition to us getting this working on 1 version of Fedora, 2
versions of Ubuntu and a wireless router I recently made the changes to
a Beaglebone Black however there is an issue with Linux USB interrupts
on that platform which makes it unusable for the moment.

Stuart.

Post by Sven-Ola Tuecke
Hey,
should be possible to use at least 2 of them at the same USB bus, but
obviously nobody wants to calculate the compression-to-bandwidth
estimation (neither driver nor OEM). Here's a hack, that seems to work
fine. Please comment.
// Sven-Ola
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[Sven-Ola Tuecke]

Hi Stuart,

thanks for commenting. Those openwrt diffs do the roughly the same:
setting dwMaxPayloadTransferSize to something > 1024 which in turn seems
to lower USB bus usage to something around 50%. Maybe someone with USB
knowledge should rework those calculations anyhow, since with
uncompressed YUV images that codepath does not produce correct behaviour
in my setup. Also, your USB irq platform probs may not be linked
directly to that maxsize fiddeling...

Anyhow: I have a working Uvcvideo DKMS setup, so mission accomplished
for me...

// Sven-Ola

Post by stuart
Hi Sven,
Reik Red and I did quite a bit of work on this about 3 months ago and
http://superuser.com/questions/431759/using-multiple-usb-webcams-in-linux/1018342#1018342
https://sourceforge.net/p/linux-uvc/mailman/message/34748762/
In addition to us getting this working on 1 version of Fedora, 2
versions of Ubuntu and a wireless router I recently made the changes
to a Beaglebone Black however there is an issue with Linux USB
interrupts on that platform which makes it unusable for the moment.
Stuart.

Post by Sven-Ola Tuecke
Hey,
should be possible to use at least 2 of them at the same USB bus, but
obviously nobody wants to calculate the compression-to-bandwidth
estimation (neither driver nor OEM). Here's a hack, that seems to work
fine. Please comment.
// Sven-Ola