[alsa-devel] Fwd: ALSA queries

[Takashi Iwai]

On Thu, 09 Aug 2018 13:19:53 +0200,
Chakravarthi Pradeep wrote:
> 
> Hi Takashi,
> 
> How to enable log from ALSA lib core or ALSA core , so that I will
> come to know why trigger stop call back is getting called back by
> itself.

Do printk, tracing, whatever you can see.
We have the standard tracepoints, too, but maybe it's not what you
need.

> ring bufffer size is 57600 and minimum bytes device generates per
> period is 3200(bytes). I have read one frame is 4 bytes from below
> link.
> https://www.alsa-project.org/main/index.php/FramesPeriods
> So is it correct to give below values to snd_pcm_hardware
> .period_bytes_min = 3200 /* per interrupt device provides minimum 3200
> bytes of data*/
> .periods_min = 72 /* 3200/4 /* 4 is because of (2 (channel )*  (16 bits/2)) */

period_bytes_min is 3200 bytes, so it looks correct.
But periods_min is the minimal number of periods in a ring buffer.
It can be calculated as (min buffer size) / (max period size).


Takashi

> 
> Regards,
> Chakravarthi
> On Tue, Aug 7, 2018 at 7:13 PM Takashi Iwai <tiwai at suse.de> wrote:
> >
> > On Tue, 07 Aug 2018 15:36:22 +0200,
> > Chakravarthi Pradeep wrote:
> > >
> > > >In the case above it's in frames.  But it can be defined in bytes
> > > >depending on the hardware spec.  Some hardware defines in the time
> > > >unit (like msec), too.
> > >
> > > Can you please tell me how to define in bytes ?
> >
> > Read the source before asking like this.  If not found, read the
> > source again.  If still it's not fulfilled, ask more specific
> > questions.
> >
> > The driver doesn't define it.  Rather the driver lets ALSA PCM core
> > choose the parameters given from user-space.  But some parameters
> > might not fit with the requirement of your hardware.  For satisfying
> > it, the driver may give hw constraints to PCM core beforehand,
> > typically set in the open callback.
> >
> > > >Now you know it.  And remember that PA is often die-hard.
> > > So it means that I can not do rmmod until pulseaudio is removed , is
> > > it correct ?
> >
> > Yes.  You cannot rmmod during any program is accessing to the sound
> > device, not only PA.
> >
> >
> > Takashi
> >
> > > Regards,
> > > Chakravarthi
> > > On Tue, Aug 7, 2018 at 6:45 PM Takashi Iwai <tiwai at suse.de> wrote:
> > > >
> > > > On Tue, 07 Aug 2018 15:12:08 +0200,
> > > > Chakravarthi Pradeep wrote:
> > > > >
> > > > > Dear Takashi,
> > > > >
> > > > > Thanks for your reply.
> > > > >
> > > > > > The "period" in ALSA PCM definition represents the interval time (or
> > > > > > frames) of the periodical interrupts on the ring buffer.  If the irq
> > > > > > is issued for each 256 frames while the ring buffer size is 1024
> > > > > > frames, periods = 1024/256 = 4.  The periods_min defines the minimal
> > > > > > number of periods the hardware may accept.
> > > > >
> > > > > Is it  256 frames or  256 bytes ?
> > > >
> > > > In the case above it's in frames.  But it can be defined in bytes
> > > > depending on the hardware spec.  Some hardware defines in the time
> > > > unit (like msec), too.
> > > >
> > > > > fuser -v /dev/snd/* output is
> > > > >                                          USER
> > > > >   PID   ACCESS    COMMAND
> > > > > /dev/snd/controlC0         Dell                                   1815
> > > > > F.....           pulseaudio
> > > >
> > > > Now you know it.  And remember that PA is often die-hard.
> > > >
> > > >
> > > > Takashi
> > >
> > >
> > >
> > > --
> > > Thanks and Regards
> > > Chakravarthi Pradeep.K
> > > Ph: 91 9980434900
> > >
> 
> 
> 
> -- 
> Thanks and Regards
> Chakravarthi Pradeep.K
> Ph: 91 9980434900
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