Thanks for the feedback! I think that improved our ALSA driver
significantly (attached!)
On Tue, Oct 13, 2009 at 12:03 AM, Clemens Ladisch <clemens@xxxxxxxxxx> wrote:
> Sam Lantinga wrote:
>> I'm attaching the latest versions of the SDL audio files, and I'd
>> really appreciate it if you take a look and sanity check our code.
>
>> device = SDL_getenv("AUDIODEV"); /* Is there a standard variable name? */
>
> ALSA's devices look at certain environment variables; you are supposed
> to use names like "default" or "surround51" to get that default
> configuration.
>
>> if (channels == 6) device = "surround51";
>> else if (channels == 4) device = "surround40";
>
> The devices do not have automatic sample format/rate conversion; you
> might want to use "plug:surround.." instead.
>
>> /* This function waits until it is possible to write a full sound buffer */
>> static void ALSA_WaitAudio(_THIS)
>
> This function doesn't actually wait ...
>
>> if ( status == -EAGAIN ) {
>> SDL_Delay(1);
>> continue;
>> }
>
> Not necessary in blocking mode.
>
>> rate = spec->freq;
>> status = SDL_NAME(snd_pcm_hw_params_set_rate_near)(pcm_handle, hwparams, &rate, NULL);
>> spec->freq = rate;
>
> The returned rate could be wildly different, but I guess SDL correctly
> handles the new value in spec->freq.
>
>> /* Set the buffer size, in samples */
>> frames = spec->samples;
>> status = SDL_NAME(snd_pcm_hw_params_set_period_size_near)(pcm_handle, hwparams, &frames, NULL);
>
> This does _not_ set the buffer size.
>
>> periods = 2;
>> SDL_NAME(snd_pcm_hw_params_set_periods_near)(pcm_handle, hwparams, &periods, NULL);
>
> A bigger number of periods would make the writing of audio data less
> bursty.
>
>> status = SDL_NAME(snd_pcm_sw_params_set_start_threshold)(pcm_handle, swparams, 0);
>
> Zero doesn't really make sense; the default value 1 would be OK.
>
>> status = SDL_NAME(snd_pcm_sw_params_set_avail_min)(pcm_handle, swparams, frames);
>
> The default value is the period size anyway, so you can remove this.
> (If you change the buffer size code above to use _set_buffer_size_near,
> this call would be wrong.)
>
>
> Best regards,
> Clemens
>
--
-Sam Lantinga, Founder and President, Galaxy Gameworks LLC
Attachment:
SDL_alsa_audio.c
Description: Binary data
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