[alsa-devel] playback write error (DMA or IRQ trouble)

[Harsha priya gupta]

Is there any way to avoid the timer part? Because i do not want the cpu to
bother with anything till the hardware has done its part. after the hardware
interrupts, can i manipulate someway to get the next buffer rather than
interrupting every 1 sec to say that the period has been processed.



On Mon, Jun 2, 2008 at 3:10 PM, Takashi Iwai <tiwai at suse.de> wrote:

> At Mon, 2 Jun 2008 15:06:03 +0530,
> Harsha priya gupta wrote:
> >
> > Say if my hardware is such that it shall interrupt only after it has
> processed
> > entire sample and not ever period or sample. What will ensure that i get
> my
> > next buffer down? Will calling the snd_pcm_period_elapsed in the
> interrupt
> > function help?
>
> So, your hardware has only a single ring buffer and can issue an
> interrupt only at the end of the buffer?
>
> If so, you might need to seek for another interrupt source, such as a
> system timer.
>
>
> Takashi
>
> > On Mon, Jun 2, 2008 at 2:54 PM, Takashi Iwai <tiwai at suse.de> wrote:
> >
> >     At Mon, 2 Jun 2008 14:33:14 +0530,
> >     Harsha priya gupta wrote:
> >     >
> >     > Quick question
> >     >
> >     > From my copy function after I pass the buffer to HW, what would
> happen if
> >     i
> >     > call snd_pcm_period_elapsed.
> >
> >     It's invalid and a misdesign.
> >
> >     I guess you are misunderstanding about when to
> >     callsnd_pcm_period_elapsed().  snd_pcm_period_elapsed() is called
> when
> >     one period of samples on the hardware is *processed*.  It doesn't
> mean
> >     that the samples are transferred to the hardware.
> >
> >     Suppose that you have period_size = 48000 (frames) for 48kHz samples.
> >     Then, the first snd_pcm_period_epased() shall be called just one
> >     second after starting the PCM stream.  The second call be another one
> >     second later, and so on.  It doesn't matter how quick the copy to h/w
> >     is done (via copy callback).
> >
> >     Takashi
> >
> >     >
> >     > On Mon, Jun 2, 2008 at 1:37 PM, Takashi Iwai <tiwai at suse.de>
> wrote:
> >     >
> >     >     At Mon, 2 Jun 2008 13:26:01 +0530,
> >     >     Harsha priya gupta wrote:
> >     >     >
> >     >     > I implemented the copy function and immediately transfered
> the user
> >     block
> >     >     data
> >     >     > to the hardware.
> >     >     >
> >     >     > Correct me if am wrong;
> >     >     > .pointer implementation - passes the current buffer pointer.
> When
> >     the
> >     >     .pointer
> >     >     > function returns the size of the buffer = user buffer size
> >     logically I
> >     >     need to
> >     >     > expect the hardware to send an interrupt because buffer is
> consumed
> >     and I
> >     >     > should call snd_pcm_period_elapsed after that.
> >     >     >
> >     >     > what would happen if i call the snd_pcm_period_elapsed from
> the
> >     pointer
> >     >     > function once the buffer is consumed from hardware. Would
> that be
> >     right?
> >     >      This
> >     >     > is what i am trying to do
> >     >
> >     >     The logic is reversed.
> >     >     The pointer callback is a passive one that does nothing but
> returning
> >     >     the current h/w buffer position.  This is called either from
> >     >     snd_pcm_period_elapsed() or at the PCM status update.
> >     >
> >     >     You must call snd_pcm_period_elapsed() somewhere in your driver
> >     >     *explicitly* at the timing that one period is finished.
>  Usually,
> >     this
> >     >     is done in an IRQ handler the h/w generates at the period
> >     ("fragment",
> >     >     "half-buffer", or whatever) boundary.
> >     >
> >     >     And note that the valid value from the pointer callback is
> between 0
> >     >     and buffer_size-1 as it handles the buffer as a ring-buffer.
>  The
> >     >     value buffer_size is invalid.
> >     >
> >     >     Takashi
> >     >
> >     >     > On Mon, Jun 2, 2008 at 1:02 PM, Takashi Iwai <tiwai at suse.de>
> wrote:
> >     >     >
> >     >     >     At Mon, 2 Jun 2008 12:39:31 +0530,
> >     >     >     Harsha priya gupta wrote:
> >     >     >     >
> >     >     >     > Can anyone give me a clue as to when i would get such
> an
> >     error?
> >     >     >
> >     >     >     ... only if you give more clue what exactly you did.
> >     >     >
> >     >     >     In general, it implies that an interrupt isn't issued
> properly
> >     at PCM
> >     >     >     period boundary.
> >     >     >
> >     >     >     Takashi
> >     >     >
> >     >     > --
> >     >     > -Harsha
> >     >     >
> >     >     >
> >     >
> >     > --
> >     > -Harsha
> >     >
> >     >
> >
> > --
> > -Harsha
> >
> >
>



-- 
-Harsha