From: Takashi Iwai <tiwai@suse.de>
To: Timur Tabi <timur@freescale.com>
Cc: alsa-devel@alsa-project.org, Nobin Mathew <nobin.mathew@gmail.com>
Subject: Re: Trouble understanding ALSA's DMA buffers
Date: Tue, 12 Jun 2007 18:45:26 +0200 [thread overview]
Message-ID: <s5h645tuno9.wl%tiwai@suse.de> (raw)
In-Reply-To: <466ECB91.2030609@freescale.com>
At Tue, 12 Jun 2007 11:36:33 -0500,
Timur Tabi wrote:
>
> Takashi Iwai wrote:
>
> > Yes. And the "ping-poing" is the case that you have two periods in a
> > ring buffer.
>
> Ok, I understand the 'periods' concept now, thanks.
>
> So when/where does ALSA copy data to the DMA buffer? Isn't there supposed to be some kind
> of callback where ALSA calls the driver and says, "here's some data, please copy it to
> your DMA buffer?"
>
> Or does ALSA do all the copying itself whenever the driver calls snd_pcm_period_elapsed()?
It depends on the implementation, but usually the latter case.
The whole data-transfer task is done by ALSA PCM middle layer, and
each driver has to take care of the DMA setup -- as long as your
hardware can have a buffer on RAM. If you need to copy the data to
hardware buffer manually in some way, the things become
complicated...
Takashi
prev parent reply other threads:[~2007-06-12 16:45 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-06-11 19:57 Trouble understanding ALSA's DMA buffers Timur Tabi
2007-06-11 20:29 ` Nobin Mathew
2007-06-12 10:36 ` Takashi Iwai
2007-06-12 15:21 ` Pharaoh .
2007-06-12 15:44 ` Pharaoh .
2007-06-12 16:36 ` Timur Tabi
2007-06-12 16:45 ` Takashi Iwai [this message]
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