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@xxxxxxx> 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@xxxxxxx> 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@xxxxxxx>
> 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@xxxxxxx>
> 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
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