Re: [linux-uvc-devel] USB bandwidth allocation

[Martin O. <mar...@ho...>]

This works only with non-compressed formats which uses a lot more 
bandwidth than H264 format. Camera also supports MJPEG, which in the 
middle in bandwidth consumption.

Best regards, Martin


On 23. 08. 2017 01:32, Curt Meyers wrote:
> See this webpage for the BANDWIDTH quirk: 
> http://www.ideasonboard.org/uvc/faq/
>
> Curt
>
>
> On 08/22/2017 09:20 AM, Martin Opresnik wrote:
>> Hello,
>> we are working on a project, where we need multiple cameras connected to
>> embedded computer. For computer we have chosen odroid XU4 and for
>> cameras Logitech C920. We need at least 5 cameras running with 720p. The
>> problem we have is allocated USB bandwidth (cameras are using
>> isochronous transfer). Currently we can run 3 cameras on 720p. Image is
>> transferred in h264 compressed format. Writing on disk is done directly
>> trough memory map using V4L2 api and files on disk are really small and
>> using usbmon/wireshark shows ~1104kB/s (there should be a lot of USB
>> bandwidth left).
>> I tried same setups on my laptop and I don't get any better results, so
>> I suspect there is some space for improvement in software and it's not
>> odroid's fault. I tried changing different parameters in uvcvideo driver
>> and I think only wMaxPacketSize is affecting bandwidth allocation. And
>> changing that is reflected in non working camera.
>> Now I don't know enough about USB and linux kernel to work around this
>> problem and I would be very happy if you could give me some help or
>> directions.
>>
>> I am looking forward to hearing from you.
>>
>> Best regard, Martin
>>
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