[alsa-devel] [PATCH 2/2] pcm:plugin: Fix sound capture via MMAP access

[Takashi Iwai]

On Tue, 04 Apr 2017 08:30:18 +0200,
sutar.mounesh at gmail.com wrote:
> 
> From: Timo Wischer <twischer at de.adit-jv.com>
> 
> Distorted sound is heard if the capture device of an ioplug plugin is used,
> which is accessed through any ALSA plugin (like copy, linear, ...) via MMAP access.
> E.g. aplay -> loop -> copy -> arecord -M -> aplay -> hw:0
> As mentioned in the ALSA API (see pcm/pcm.c:942):
> The function #snd_pcm_avail_update() have to be called
> before any mmap begin+commit operation.
> 
> Signed-off-by: Timo Wischer <twischer at de.adit-jv.com>
> Signed-off-by: Mounesh Sutar <sutar.mounesh at gmail.com>

Applied this one, too.  Thanks.


Takashi

> 
> diff --git a/src/pcm/pcm_plugin.c b/src/pcm/pcm_plugin.c
> index aaea2ab..ec57f6e 100644
> --- a/src/pcm/pcm_plugin.c
> +++ b/src/pcm/pcm_plugin.c
> @@ -490,7 +490,14 @@ static snd_pcm_sframes_t snd_pcm_plugin_avail_update(snd_pcm_t *pcm)
>  			snd_pcm_uframes_t slave_offset;
>  			snd_pcm_uframes_t slave_frames = ULONG_MAX;
>  			snd_pcm_sframes_t result;
> -
> +			/* As mentioned in the ALSA API (see pcm/pcm.c:942):
> +			 * The function #snd_pcm_avail_update()
> +			 * have to be called before any mmap begin+commit operation.
> +			 * Otherwise the snd_pcm_areas_copy will not called a second time.
> +			 * But this is needed, if the ring buffer wrap is reached and
> +			 * there is more data available.
> +			 */
> +			slave_size = snd_pcm_avail_update(slave);
>  			result = snd_pcm_mmap_begin(slave, &slave_areas, &slave_offset, &slave_frames);
>  			if (result < 0) {
>  				err = result;
> -- 
> 2.7.4
>