Thanks for your reply.
> > As far as I understand, the easiest solution would be to have a pcm_plug
> > plugin inbetween the alsa application and the pcm_jack plugin, to take
> > care of sample rate and data format conversion. Then the pcm_jack plugin
> > simply restrict it configuration space to the sample rate and data format
> > (float) supplied by the jack server. Is this the right approach? Then,
>
> Yep.
Okay, good to know I am on the right track. Now, as a first step, I thought
I'd restrict myself to simple read/write (interleaved and non-interleaved)
access, and mmap would come later. But if I set the access mask in my
snd_pcm_jack_hw_refine to
snd_pcm_access_mask_set(&access_mask, SND_PCM_ACCESS_RW_INTERLEAVED);
snd_pcm_access_mask_set(&access_mask, SND_PCM_ACCESS_RW_NONINTERLEAVED);
then the pcm_plug fails
ALSA lib pcm_plug.c:714:(snd_pcm_plug_hw_refine_schange) Unable to find
an usable access for 'myplug'
Even though from the application I request non-mmap access (aplay), the
plug plugin apparently requieres mmap access from it's slave. Is this
correct?
If I do use mmap, a shmid is obtained from the pcm_jack plugin through
the channel_info op. I looked at pcm_null, where the shmid is
set in the mmap op, but when I try to use the some construction, I run
into problems, because (as in pcm_null.c:729)
if (!(pcm->info & SND_PCM_INFO_MMAP)) {
is false, so the shmid is not set, so after passing through
snd_pcm_jack_mmap and snd_pcm_jack_channel_info, I get a
ALSA lib pcm_mmap.c:367:(snd_pcm_mmap) shmat failed: Identifier removed
I don't understand how this works in pcm_null... Is the mmap op the correct
place to set the shmid? And how come the channel_info op is called when
appearently we are using mmap?
> > what would be the right place to do this? In the hw_refine or in the
> > hw_param function? Or somewhere else even? And how - what _snd_pcm helper
> > functions should I best use?
>
> Well, I think that it needs a bit deeper introduction to the alsa-lib
> plugin system. I'm actually working on dmix plugin and facing with same
> problems.
Yes... But there is no documentation that describes that plugin system
internals, right?
Maarten
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