[wdmaudiodev] Re: Debugging USB audio at the hardware level

  • From: Tim Roberts <timr@xxxxxxxxx>
  • To: wdmaudiodev@xxxxxxxxxxxxx
  • Date: Thu, 17 Sep 2009 10:27:26 -0700

Martin Gagnon wrote:
> I know this is a software-focused group for audio, but many of you may
> know a thing or two about USB protocol messages to a USB audio device.
> Here is the situation, we’re dealing with a C-Media audio device
> CM6206, using MS usbaudio.sys driver. The C-Media chip is sitting
> behind a NEC USB2.0 hub that’s connected to a NEC USB2.0 host
> controller, itself connected to a PLX PCIe switch. Using Windows XP
> SP3, the driver installs fine, typical audio playback works fine
> (directsound or wave output). However, when we concurrently enable
> video and audio, for example playing back a movie in full screen, with
> no hardware video decoding, we lose audio after “a while”, and can’t
> get it back. However, the Windows default sounds (for example system
> beep or logoff sounds) are still working fine. The interval of time
> before we lose the audio varies with the graphics activity in the
> system, as well as with various systems of various speeds, so it can
> take 5mins or it can take 1 day. We tried the C-Media driver as well
> and got the same symptom. We also tried different USB audio chip
> manufacturers (including TI) to no avail.

So, is endpoint 2 the "sync" endpoint for the audio out data on endpoint

> So we looked at the USB transactions on the USB bus going into the USB
> audio chip. We note a series of OUT transactions followed by IN
> transactions, usually containing a “NACK” message. This goes on for as
> long as the audio plays back fine. Then we get a series of OUT
> transactions with no corresponding IN transactions, then we get a
> Reset event.

Did you notice that the final OUT transaction is damaged?  Is that
typical of the captures you've seen?

Is the NEC hub a constant in all of this?

Tim Roberts, timr@xxxxxxxxx
Providenza & Boekelheide, Inc.

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