[alsa-devel] Errors iterating over PCM stream hints and opening based on NAME/IOID

[Trent Reed]

Hey Takashi,

Glad that this issue with bidirectional PCM hints was patched. :)
I appreciate your help and input!

Thanks,
- Trent Reed

On Thu, May 12, 2016 at 7:38 AM, Takashi Iwai <tiwai at suse.de> wrote:
> On Sat, 07 May 2016 05:19:45 +0200,
> Trent Reed wrote:
>>
>> Hey All,
>>
>> (Tried to send an email earlier, it didn't seem to send?)
>>
>> I'm trying to understand ALSA, having a little trouble with some
>> errors that I can't ration over.
>> Gist Repro: https://gist.github.com/TReed0803/353ce27d37bc1ebe965854ea88c8b97b
>>
>> Whenever I run the above simple code (iterate over PCM stream hints,
>> open for Playback/Capture depending on IOID; output also provided at
>> link above) I notice that I sometimes hit errors. I'm having trouble
>> understanding these errors, because as I understand I'm using the ALSA
>> library correctly. For example, dmix is telling me that it "Only
>> supports playback streams", well then, why does the hint IOID return
>> that it supports capture as well? (same for dsnoop).
>
> Oh, these are real bugs.  They shouldn't have been listed as
> bidirectional, indeed.  The fix patches are below.
>
>> More confusing
>> are the "ALSA lib pcm_route.c:867:(find_matching_chmap) Found no
>> matching channel map" errors.
>
> This is a bit more complicated.  I suppose you're testing with
> HD-audio, right?  HD-audio has a restriction that it accepts only even
> numbered streams (2, 4, 6, 8).  The error comes from the definition of
> surround21, i.e. the odd numbers.  But, you can still use this
> definition by wrapping with plug, so that the missing one channel is
> filled automatically while using the given channel allocation.
>
> thanks,
>
> Takashi
>