[LAU] reducing xruns (System configuration)

[Chris Caudle]

On Wed, July 18, 2018 4:20 pm, Will Godfrey wrote:
> Something nobody seems to have mentioned is the command lsusb.

Of course, thanks for bringing that up.  The original poster provided
output that shows his device is using a PCM2902C from Texas Instruments.

> USB2 speeds on modern cards can easily
> manage 64/2 at 48k. Indeed, mine can
> (just) manage 16/2 at 48k.

The PCM2902C is a "full speed" device, not "high speed," so the
transmission window is 1ms, not 125us.  As the document you linked pointed
out you have to assume that the start of transmission can shift within the
window, so you have to allow for two transmission windows worth of time. 
Given that the device in  use is not high speed I think my original
warning applies, 1.3ms latency is feasible for some devices but not all,
doubling the buffer size would provide some breathing room, increasing the
number of buffers from 2 to 3 also would.

And of course as you pointed out moving the audio device to a USB bus
without other devices would help, and as Ralf pointed out getting
threadirqs applied to the kernel command line so that RT scheduling will
work would help as well.

-- 
Chris Caudle