What is the format of dma_area?

What is the format of dma_area?

[Bill Gatliff]

Guys:


I'm trying to write a PCM driver that uses an AC97 codec, on an ARM 
host, but no DMA.  (Please pardon some of my terminology, I'm a bit of 
an ALSA noob).

My trigger() looks something like this:

int *buffer;
int bytes;
...
  switch (cmd) {
  case SNDRV_PCM_TRIGGER_START:
    bytes = frames_to_bytes(substream->runtime, 
substream->runtime->period_size);
    buffer = substream->runtime->dma_area;
...

Then, I copy *buffer++ out to the codec one 32-bit chunk (truncated to 
20 bits) at a time.

One thing I don't understand is how dma_area is formatted.  Is it a 
stream of integers, like this?

int dma_area[channels][samples];

... or like this?

int dma_area[samples][channels];

... or what?  I'm having trouble figuring out where the left- and 
right-channel data is in the dma buffer.


Thanks!


b.g.

-- 
Bill Gatliff
bgat@billgatliff.com



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Re: What is the format of dma_area?

[Takashi Iwai]

At Thu, 06 Oct 2005 22:15:49 -0500,
Bill Gatliff wrote:
> 
> Guys:
> 
> 
> I'm trying to write a PCM driver that uses an AC97 codec, on an ARM 
> host, but no DMA.  (Please pardon some of my terminology, I'm a bit of 
> an ALSA noob).
> 
> My trigger() looks something like this:
> 
> int *buffer;
> int bytes;
> ...
>   switch (cmd) {
>   case SNDRV_PCM_TRIGGER_START:
>     bytes = frames_to_bytes(substream->runtime, 
> substream->runtime->period_size);
>     buffer = substream->runtime->dma_area;
> ...
> 
> Then, I copy *buffer++ out to the codec one 32-bit chunk (truncated to 
> 20 bits) at a time.
> 
> One thing I don't understand is how dma_area is formatted.  Is it a 
> stream of integers, like this?
> 
> int dma_area[channels][samples];

It's called "non-interleaved" format in general.

> ... or like this?
> 
> int dma_area[samples][channels];

It's "interleaved" format.

It's up to you and hardware.  Set the appropriate bit flag in pcm
hardware info field.


Takashi


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Re: What is the format of dma_area?

[Bill Gatliff]

Takashi:

Takashi Iwai wrote:

>It's up to you and hardware.  Set the appropriate bit flag in pcm hardware info field.
>  
>

Thanks!  Both for the information and for the quick reply!!


b.g.

-- 
Bill Gatliff
bgat@billgatliff.com



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Power Architecture Resource Center: Free content, downloads, discussions,
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