Re: Buffer management questions

[Adrian McMenamin <adrian@mcmen.demon.co.uk>]

On Mon, 2006-03-13 at 11:24 -0800, Carlos Munoz wrote:
> Hi all,
> 
> I'm writing my first alsa driver and I have the following questions 
> regarding buffer management (I've read all the documents in the alsa 
> site but none answered my questions):
> 
> How is the sound data replenished in the dma buffer for playback ? I 
> call snd_pcm_lib_malloc_pages() to allocate the buffer. I assume when 
> the trigger function is called, there is valid data in the buffer. 
> However, once the driver sends all the data in the buffer, how does it 
> get more data ? Should I assume the data is there and just wrap around 
> the buffer ?
> 

Just been through all this myself :)

The alsa middle layer will handle this for if your driver is coded
correctly. In my case that means having a timer check that a period has
been played out, transferring new bytes across and then calling
snd_pcm_period_elapsed which manages the refill - give us some more
details of your hardware and I am sure others can help 




> I'm used to the write()/read() function calls to pass data in/out of 
> drivers, but don't yet understand how data is passed in the alsa model. 
> Any help is appreciated.
> 

The middle layer does most of the work for you though the implementation
details depend on how your hardware works. you don't need a write()


> Thanks,
> 
> 
> Carlos
> 
> 
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