Re: Zero Packets in Isochronous Transfer Reception

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On Sat, 30 Jun 2018, R0b0t1 wrote:

> Hello,
> 
> My code is a userspace application using libusb for now, but this
> seems the best place to ask.
> 
> I repurposed some USB audio class device code. At this point I've only
> changed the descriptor to report as vendor class so nothing else grabs
> the device. I can receive and play PCM audio from the device, but
> there is popping and clicking. The program I am using is attached; it
> is written in Python. The data is saved to RAM and then written to
> disk.
> 
> The device does not implement the synchronization aspect of the USB
> audio class and when it registers as a microphone a normal userland
> can read it properly.
> 
> During testing I think I noticed behavior related to my issue - for
> some reason there will be long runs of zero returned or no data
> returned. Usually this happens when a single transfer is scheduled.
> Many transfers in a row tend to report the data properly, but from the
> audible results I get it seems that runs of zeros still seem to slip
> in.
> 
> The problem seems more noticeable when using the Python libusb
> bindings but it still exists when using libusb directly. Can anyone
> suggest what to look into?

Have you tried using usbmon to capture the data as it is received by 
the kernel?

Alan Stern

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