Re: FW: DMA producer/consumer

[Takashi Iwai <tiwai@suse.de>]

At Thu, 11 Mar 2004 18:43:39 +0100 (CET),
Jaroslav wrote:
> 
> On Thu, 11 Mar 2004, Takashi Iwai wrote:
> 
> > unfortunately, the current implementation of ALSA PCM middle layer
> > isn't well suited for this kind of hardwares.  it'll be a bit more
> > complicated than you think.
> 
> I don't think that's this case. I'm not sure, if the basic midlevel 
> mechanism is understood: The midle level code expects that driver 
> start/stop the stream in the trigger callback, so if you can queue
> more 'periods' into the DMA engine, do it and abort/pause the transfer
> only the trigger callback request. You don't need to check appl/hw_ptr
> in the lowlevel code.

hmm, if i understand correctly, this DMA engine needs the update of
DMA queue.  i.e. the driver needs to feed chunks manually in prior
to the DMA start, and continues feeding the available chunks after
that as long as the stream is running.  this is somewhat analogous
with the case with the external hardware buffer.

correct me if i'm wrong.


Takashi


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