Re: USB audio devices

[Takashi Iwai <tiwai@suse.de>]

At Wed, 10 Mar 2004 10:08:26 +0100 (CET),
Jaroslav wrote:
> 
> On Wed, 10 Mar 2004, Clemens Ladisch wrote:
> 
> > Jaroslav Kysela wrote:
> > 
> > > On Tue, 9 Mar 2004, Takashi Iwai wrote:
> > >
> > > > BTW, the USB audio is another headache. the current ALSA PCM model isn't
> > > > perfectly suitable for the devices like USB audio.
> > >
> > > Unfortunately I don't see a better model.
> > 
> > Conceptually, USB devices have variable-sized periods.  The question
> > is whether we actually want to allow this in the API.  Probably not.
> 
> What this does mean? I though that the period size is specified with time 
> (1ms) for USB, isn't it? I think that we can describe this constraint 
> with the refine algorithm.

the period "time" is constant but the sample numbers in this period
varies from time to time because of tuncation to integer or due to
sync mode.  so far, we assume that the samples in a period is
constant.

we have some cases which we can't handle properly:

1) the period time is constant but the period size is variable
   e.g. USB-audio

2) the period size is constant but the period time is variable
   e.g. synchronization with another stream or clock source
        vari-speed stream

3) both period size and time are variable
   ???  not known


Takashi


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