Re: New ALSA Driver

[James Courtier-Dutton <James@superbug.co.uk>]

K.Fetscher@t-online.de wrote:
> Hi,
> 
> I wan't to program an ALSA driver for my custom ARM based Cirrus-EP9312 board.
> 
> The driver starts with the initialisation of the hardware, with 
> snd_card_new(...), snd_pcm_new(...), the request for the DMA-Controller, 
> programming snd_pcm_set_ops(...) and 
> snd_pcm_lib_preallocate_pages_for_all(...).
> 
> After that, I can see the card in the /proc/asound/card0/... filesystem.
> 
> 
> When I start playing a song with aplay, ALSA calls hw_params(..), prepare(..)  
> and trigger(..) with command SNDRV_PCM_TRIGGER_START. After that, all stops 
> until I make a CTRL C (after that, it terminates with hw_free and close). Is 
> it correct, that runtime->dma_addr is 0 (runtime->size is 1000 and 
> runtime->period is 400) ?
> 
> 
> I have looked into some drivers for the parameters of 
> snd_pcm_lib_preallocate_pages_for_all(...). There are different types for the 
> DMA type and I don't know, which is the correct type (at the moment, I use 
> SNDRV_DMA_TYPE_CONTINUOUS).
> 
> Thanks
> 
> Klaus  
> 

It is difficult to answer your questions without seeing the source code 
itself.
One thing to note is that the DMA has two different addresses:
runtime->dma_addr is the physical memory address. i.e. the address to 
give to the sound card hardware.
runtime->dma_area is the virtual address. i.e. the address the kernel 
CPU writes to.

I only know how x86 CPUs work, so ARM might be different in this respect.

James



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