Re: PCM driver only plays tiny portion of clip

[Lee Revell <rlrevell@joe-job.com>]

On Fri, 2006-03-03 at 07:42 +0000, Adrian McMenamin wrote:
> On Fri, 2006-03-03 at 08:27 +0100, Clemens Ladisch wrote:
> > Adrian McMenamin wrote:
> > > I think I have a good idea why my it is not working now - the DMA
> > > routine which transfers sound samples from the main CPU memory to the
> > > ring buffer of the hardware (which is effectively in a different memory
> > > space) is in a kernel thread which, in essence, never gets rescheduled -
> > > so the app thinks there is sound to be transferred but it never is -
> > > hence it gets wedged.
> > > 
> > > To fix that I need to know what the alsa subsystem calls inside the
> > > driver when it wants a DMA transfer to resume - I have to reschedule the
> > > kernel thread there.
> > 
> > ALSA doesn't call the driver.  It assumes the hardware runs by itself.
> > 
> > If your hardware doesn't issue some interrupt regularly, you have to use
> > a timer.
> > 
> It does have an interrupt - I am working on the idea of having the
> kernel thread sleep and then wake up on the interrupt
> 

Also see

http://www.alsa-project.org/~iwai/writing-an-alsa-driver/x1401.htm

External Hardware Buffers
Some chips have their own hardware buffers and the DMA transfer from the
host memory is not available. In such a case, you need to either 1)
copy/set the audio data directly to the external hardware buffer, or 2)
make an intermediate buffer and copy/set the data from it to the
external hardware buffer in interrupts (or in tasklets, preferably). 

Doesn't this describe your hardware exactly?

Lee



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