Re: pointer callback in pcm

[Adrian McMenamin <adrian@mcmen.demon.co.uk>]

On Fri, 2006-03-10 at 21:16 +0100, Takashi Iwai wrote:

> 
> Hm, I've not checked your code and thread due to lack of my free time
> for ALSA recently, but the symptom above sounds like you implemented
> copy callback but still using mmap.
> 

No, I'm not using copy or mmap (the code is at
http://newgolddream.dyndns.info/cgi-bin/cvsweb these days)


> The copy callback is designed basically only for read/write transfer.
> In the mmap mode, of course, such read/write transfer is eliminated,
> and no copy action occurs.
> 
> Thus, first try not to set MMAP flag and let alsa-lib use the
> traditional read/write method.
> 
> Some hardwares have actually separate h/w buffer and the memory
> buffer (s/w buffer).  Even with such hardwares, mmap can be
> implemented.  Instead of DMA transfer by hardware, the driver copies
> data between h/w and s/w buffers on demand, namely, before starting
> the stream (in trigger callback) and when each period is consumed (via
> ack callback).


This is quite like my device - but I know nothing about the ack device


> 
> There are userful functions for such a case, found in pcm-indirect.h.
> They are used emu10k1 FX mode and cs46xx.
> 

I'll look

> 
> HTH,
> 
> Takashi



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