Re: intel8x0 with ICH5 and ALC650 multichannel problems.

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

Please ignore this. The "buffer/period size problem" was a bug in the 
application code.

James Courtier-Dutton wrote:
> I have a Motherboard with the ICH5 and ALC650 so I use the intel8x0 alsa 
> kernel driver. (Currently the version from 2.6.0-test4.)
> I have managed to get SPDIF passthru working. (I posted the patch some 
> time ago, and it is now in 2.6.0-test4)
> I cannot get multichannel working.
> The motherboard has 5 audio jacks. mic, line-in, front, rear, center-lfe.
> If I output just 2 channels, the sound comes out perfectly from the 
> "front" jack.
> If I output in 4 or 6 channels, the sound fails on all channels.
> Sometime I hear a short burst of sound on the front channel, but hardly 
> ever.
> I am pretty sure that this is a buffer/period size problem.
> My application has code is (see below)
> Which function in intel8x0.c interacts with the buffer and period sizes?
> The "snd_pcm_hw_params_set_buffer_time_near" gets full buffer_time for 
> stereo, but for 6 channels it does not, and has to reduce the buffer 
> size to some limits determined by the hardware. I think it is this 
> "limiting/contraint" code that is not working correctly.
> Can anyone provide me with pointers so that I could fix this bug ?
> 
> Cheers
> James
> 
> 
> /* set the ring-buffer time [us] (large enough for x us|y samples ...) */
>   dir=0;
>   err = snd_pcm_hw_params_set_buffer_time_near(this->audio_fd, params, 
> &buffer_time, &dir); /* buffer_time before call = 1000000 */
>   if (err < 0) {
>     printf ("audio_alsa_out: buffer time not available\n");
>     goto __close;
>   }
>   printf ("audio_alsa_out: Got %d buffer_time, wanted %d\n",buffer_time, 
> BUFFER_TIME);
>   err = snd_pcm_hw_params_get_buffer_size(params, &(this->buffer_size));
>   /* set the period time [us] (interrupt every x us|y samples ...) */
>   dir=0;
>   period_size=this->buffer_size/8;
>   err = snd_pcm_hw_params_set_period_size_near(this->audio_fd, params, 
> &period_size, &dir);
>   if (err < 0) {
>     printf ("audio_alsa_out: period time not available");
>     goto __close;
>   }
>   dir=0;
>   err = snd_pcm_hw_params_get_period_size(params, &period_size, &dir);
>   if (2*period_size > this->buffer_size) {
>     printf ("audio_alsa_out: buffer to small, could not use. 
> period_size=%ld, buffer_size=%ld\n", period_size, this->buffer_s
> ize);
>     goto __close;
>   }
> 



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