[alsa-devel] clarification on mmap

[Takashi Iwai]

At Tue, 24 Feb 2009 10:43:54 +0530,
Harsha, Priya wrote:
> 
> I have another question on the same. 
> 
> What are the runtime->transfer_ack_begin and transfer_ack_end used
> for?

I don't know, too, why these were introduced :)  It's nowhere used.
We should remove them, I think.

> Will this help me understand when the runtime->dma_area are
> updated be it MMAPed buffer or not.

No, they are callbacks called from snd_pcm_period_elapsed().
And snd_pcm_period_elapsed() is the function the driver must call to
update the buffer.


Takashi

> 
> Thanks,
> Harsha
> 
> 
> -----Original Message-----
> From: alsa-devel-bounces at alsa-project.org [mailto:alsa-devel-bounces at alsa-project.org] On Behalf Of Harsha, Priya
> Sent: Tuesday, February 24, 2009 10:24 AM
> To: Takashi Iwai
> Cc: alsa-devel at alsa-project.org
> Subject: Re: [alsa-devel] clarification on mmap
> 
> Thanks Takashi. Then what would be the best way to know when the mmaped buffer has been filled. So that I can take action to send it to the hardware? 
> 
> Should I use the runtime->control->appl_ptr or runtime->status->appl_ptr to get the position the app has filled?
> 
> -----Original Message-----
> From: Takashi Iwai [mailto:tiwai at suse.de] 
> Sent: Tuesday, February 24, 2009 12:55 AM
> To: Harsha, Priya
> Cc: alsa-devel at alsa-project.org
> Subject: Re: clarification on mmap
> 
> At Mon, 23 Feb 2009 22:21:24 +0530,
> Harsha, Priya wrote:
> > 
> > Thank you. Can I use .ack callback to know that the mmaped buffer
> > has been filled by the user?
> 
> Not really.  It's just for explicit read/write modes.
> 
> > How would I know how much the user has
> > written into the buffer that time?
> 
> You can check appl_ptr at any time.  This corresponds to the position
> the app has filled.
> 
> 
> Takashi
> 
> > Would I need to have the pointers
> > calculated and tracked myself or is there a field in the structures
> > that I can read and find out? 
> > 
> > -----Original Message-----
> > From: Takashi Iwai [mailto:tiwai at suse.de] 
> > Sent: Monday, February 23, 2009 8:57 PM
> > To: Harsha, Priya
> > Cc: alsa-devel at alsa-project.org
> > Subject: Re: clarification on mmap
> > 
> > At Mon, 23 Feb 2009 18:59:11 +0530,
> > Harsha, Priya wrote:
> > > 
> > > Hi,
> > > 
> > > I have a question on mmap. If I give my .info to be _MMAP and
> > > _MMAP_VALID. Will ALSA framework internally take care of mmap-ing
> > > the kernel buffer that has been pre-allocated in the .probe call? Do
> > > I need to do anything special to mmap a kernel buffer into user
> > > space? Just accessing the runtime->dma_area would allow me to access
> > > user data right? 
> > 
> > Yes.  The buffers allocated via preallocator are supposed to be
> > mmappable, so you can simply pass _MMAP* flag there.
> > 
> > 
> > Takashi
> > 
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