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@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@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