Stereo or mono - how to tell, what to do?

Stereo or mono - how to tell, what to do?

[Adrian McMenamin]

I want to add the capacity to play stereo samples to my Dreamcast sound
driver.

The hardware does not support interleaved samples and in the OSS driver
I simply separated out the input stream into two different buffers and
transferred them separately into the hardware's memory. Can I do the
same with ALSA or is there some middle layer magic I should be aware of?

And how can my driver tell if the incoming samples are stereo or not. In
OSS this was all done through the SNDCTL_DSP_STEREO and
SNDCTL_DSP_CHANNELS ioctls, how do I do it in ALSA (I need to inform the
hardware to expect two channels and not one).

Adrian




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Re: Stereo or mono - how to tell, what to do?

[James Courtier-Dutton]

Adrian McMenamin wrote:
> I want to add the capacity to play stereo samples to my Dreamcast sound
> driver.
>
> The hardware does not support interleaved samples and in the OSS driver
> I simply separated out the input stream into two different buffers and
> transferred them separately into the hardware's memory. Can I do the
> same with ALSA or is there some middle layer magic I should be aware of?
>   
You can get alsa-lib to send either interleaved or non-interleaved 
samples to your driver.
You just tell alsa-lib which format you like, and set the 
snd_pcm_hardware .info parameter.
I have not looked into how alsa-lib informs the driver of the 
non-interleaved nature of the samples. You might have to look into that 
yourself.
Probably something in the snd_pcm_runtime structure.
> And how can my driver tell if the incoming samples are stereo or not. In
> OSS this was all done through the SNDCTL_DSP_STEREO and
> SNDCTL_DSP_CHANNELS ioctls, how do I do it in ALSA (I need to inform the
> hardware to expect two channels and not one).
>
> Adrian
>
>   
You get all that information from the prepare() callback.
The parameter passed is struct snd_pcm_substream *substream.
substream->runtime->rate
substream->runtime->format
substream->runtime->channels
substream->runtime->buffer_size
substream->runtime->period_size
substream->runtime->periods





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