Re: Misbehaving Alder Lake-N PCH USB 3.2 xHCI Host Controller

["Michał Pecio" <michal.pecio@gmail.com>]

I believe what happens is that in full duplex, either by request from
Jack or on its own, snd-usb-audio attempts to synchronize the playback
and recording streams by scheduling packets to move in specific USB
(micro)frames.

With playback only, the queued packets are only marked "ASAP" and the
hardware can cheat by delaying them to the next frame if either:
- it fails to do the transfer on time for internal reasons
- we fail to queue the transfer before its due time

See discussion in xHCI spec 4.10.3.1, 4.10.3.2.

Regarding capture, snd-usb-audio seems to always queue about 10 packets
or so. Latency depends only on the hardware returning them quickly and
no delays in the IRO-drivers-application pipeline. There is almost zero
risk that the URBs won't be resubmitted on time and the hardware will
face either an empty queue or an already stale packet.

That being said, I'm seeing Missed Service Errors on the recording side,
so it's possible that in my case the ASmedia controller is to blame...