Re: Suggestion regarding alsa driver writing documentation.

[Takashi Iwai <tiwai@suse.de>]

Hi James,

could you create a patch to the source
(alsa-kernel/Documentation/DocBook/writing-an-alsa-driver.tmpl)?

it's just a DocBook format.  the tmpl extension is used to allow the
inclusion from the kernel source, although this document doesn't do
it.


thank,s

Takashi

At Sat, 08 May 2004 19:33:51 +0000,
James Courtier-Dutton wrote:
> 
> I have been helping some people with writing alsa drivers.
> One thing that they did not totally understand from the alsa 
> documentation was the concept of frames.
> To help with this, could we add a html link between in the following 
> document: -
> http://www.alsa-project.org/~iwai/writing-an-alsa-driver/x490.htm
> 
> In section: -
> /* pointer callback */
> 
> pointing to: -
> http://www.alsa-project.org/~iwai/writing-an-alsa-driver/x537.htm
> 
> In Section: -
> PCM Configurations
> 
> Where it explains about what a "frame" is.
> I think it would be helpful to also explain that the document: -
> http://www.alsa-project.org/~iwai/writing-an-alsa-driver/x490.htm
> 
> has a line: -
> current_ptr = mychip_get_hw_pointer(chip);
> 
> I think that comments should be added close to that line to say: -
> "
> The pointer value obtained from the hardware is likely to be a byte 
> offset within the buffer. In order to convert this value to a type 
> "snd_pcm_uframes_t" , that is required as the return value, use the 
> following code: -
> return bytes_to_frames(substream->runtime, pointer);
> 
> An explanation of what a "frame" is can be found at http://xyz
> "
> 
> Or just change the document example code: -
> /* pointer callback */
>    static snd_pcm_uframes_t
>    snd_mychip_pcm_pointer(snd_pcm_substream_t *substream)
>    {
>            mychip_t *chip = snd_pcm_substream_chip(substream);
> -          unsigned int current_ptr;
> +          unsigned int current_byte_ptr;
> 
>            // get the current hardware pointer
> -          current_ptr = mychip_get_hw_pointer(chip);
> -          return current_ptr;
> +          current_byte_ptr = mychip_get_hw_pointer(chip);
> +          return bytes_to_frames(substream->runtime, current_byte_ptr);
> 
>    }
> 
> 
> Cheers
> James
> 
> 
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