On 10/08/2007 09:14 PM, Bill Unruh wrote:
> On Mon, 8 Oct 2007, Peteris Krisjanis wrote:
>
>>> Introducing a /proc/asound/card0/pcm0{p,c}/hw_limits or similar might
>>> not be a bad idea though?
>>
>> That would be good idea, with completion with 'alsainfo' about device.
>>
>> How to do that properly, any clues before I try to sink my teeths in
>> ALSA code?
>
> Is this even possible? Ie, do sound cards actually tell you what their
> max or min hardware capabilities are and what info might you put into
> here? Ie, some cards can do 2 or 4 or 5.1 channel output. Do you put that
> in? And re speed, does the card actually advertise what speeds it
> supports, or is it more a matter of trying and if it does not support it,
> it rejects it.
It's really only about communicating what the _driver_ accepts (ie, tells us
the hardware can do). That is, basically export the snd_pcm_hardware struct
for the stream.
It could also be done in userspace by opening the stream and quering the
format_mask, channels and rates and stuff and I'll look into that a bit as a
followup to the rates_min/max thing that I posted if only as a template
thingy, but unless I'm missing it, I don't believe there's actually a way to
get the information from userspace without opening the "hw" device, and that
one only allows "subdevices_count" concurrent opens, meaning you'd have to
stop things talking to your soundcard if it has just one (normal).
Exposing it directly in /proc/asound would be the way. Peteris; if you'll be
looking, note that rates (and channels) might not be continuous between
their min and max or anything; mostly it's enumerated stuff. Looking at the
/proc/asound/card0/pcm0p/sub0/hw_params file generation probably helps (but
that just exports the currently selected paramters, not all possible).
Rene.
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