uaudio in full duplex

Kazuhito HONDA kazuhito at
Sun May 1 08:44:16 PDT 2005

From: Hans Petter Selasky <hselasky at>
Subject: Re: uaudio in full duplex
Date: Thu, 28 Apr 2005 15:47:41 +0200

> On Friday 22 April 2005 06:39, Kazuhito HONDA wrote:
> > the uaudio driver doesn't allow USB devices to
> > open playback and record channel pipe, simultaneously,
> > if in FreeBSD-stable, at line 3650 of uaudio.c as below:
> >
> >         if ((sc->sc_playchan.pipe != NULL) || (sc->sc_recchan.pipe !=
> > NULL)) return (-1);
> >
> > If you do comment-out it, you may be able to read and write several time.
> > But USB low-level driver soon freezes with eternal errors messages.
> > I haven't found its cause.
> What does the error messages say? It might be a bug in the UHCI driver, 
> because it does currently not check when isochronous transfers are 
> inserted in time !

Its message is `early return'.  
This message is included in ohci.c, and isn't included in uhci.c. 
And we (I and Artem Ignatiev) found that full duplex on uaudio 
work with UHCI without any problem, but don't work with OHCI.

Kazuhito HONDA

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