[alsa-devel] implement delay in ioplug alsa plugin

[Takashi Iwai]

At Wed, 19 Aug 2009 12:29:59 +0200,
Stefan Schoenleitner wrote:
> 
> Hi,
> 
> I managed to write an ioplug plugin which dumps a raw PCM stream to a
> file (similar to the way the file or tee plugins do, but without a slave
> device).
> 
> However, instead of immediately writing all the samples to the file, I
> would like to add some delay so that the samples are written to the file
> in real time at the frequency of the sampling rate.
> 
> Thus if there is a single channel stream with 16bits being played at a
> sampling rate of 8kHz, each 1/8000sec exactly 16 bits should be written
> to the file.
> 
> The reason for this is that I have a DSP attached over SPI which needs
> exactly one audio sample per interval.
> In order to talk to the DSP there is a SPI device-file which my ioplugin
> would use to write the samples to.
> 
> What is the best way to implement such a delay ?
> 
> I'm pretty sure that just adding some usleep calls() won't work very
> well, since the write operations to the device file probably don't take
> the same amount of time every time.
> Maybe it would work with non-blocking writes to the device file and a
> high precision timer ?

hrtimer would be the most accurate method, I guess.


Takashi