Hi All,
It seems that there is a bug in the PXA ALSA drivers which causes an
earlier section of the circular audio buffer to be played erroneously at
the end of playback when using aplay.
The bug occurs because runtime->period_size is not an integer multiple
of runtime->buffer_size. When a section of audio to be copied to the
buffer is less than a period size, aplay uses runtime->period size to
pad the section with zeros to ensure that the audio stream is an integer
multiple of runtime->period_size. This is important as ALSA can only
stop playback on the period boundary.
Example:
period_size = 32
buffer_size = 90
audio_size = 180
aplay pads the audio with zeros to be an integer multiple of period_size
so:
audio_size(padded) = 192
This will fill the buffer twice with 12-bytes left over. Therefore,
the first period will have 12 bytes of silence and 20 bytes of data
from earlier in the audio stream. The ALSA core will not stop until
the entire buffer is empty, thus the 20-bytes of earlier data will be
played before stopping. The solution is to add a constraint to force
the
runtime->buffer_size to be an integer multiple of runtime->period_size.
I've appended a patch to do this.
Kind Regards,
Andrew
PATCH FOLLOWS
Signed-off-by: Andrew Johnson <ajohnson <at> intrinsyc.com>
--- a/alsa-kernel/sound/arm/pxa2xx-pcm.c 2007-01-08
10:37:34.000000000 -0800
+++ b/alsa-kernel/sound/arm/pxa2xx-pcm.c 2007-01-05
17:59:27.000000000 -0800
@@ -137,7 +137,7 @@ static int pxa2xx_pcm_trigger(struct snd
return ret;
}
-static void pxa2xx_pcm_dma_irq(int dma_ch, void *dev_id)
+static void pxa2xx_pcm_dma_irq(int dma_ch, void *dev_id, struct pt_regs
*regs)
{
struct snd_pcm_substream *substream = dev_id;
struct pxa2xx_runtime_data *rtd =
substream->runtime->private_data;
@@ -213,6 +213,10 @@ static int pxa2xx_pcm_open(struct snd_pc
if (ret)
goto out;
+ ret = snd_pcm_hw_constraint_integer(runtime,
SNDRV_PCM_HW_PARAM_PERIODS);
+ if (ret < 0)
+ goto out;
+
ret = -ENOMEM;
rtd = kmalloc(sizeof(*rtd), GFP_KERNEL);
if (!rtd)
--- a/alsa-kernel/sound/soc/pxa/pxa2xx-pcm.c 2007-01-08
10:37:34.000000000 -0800
+++ b/alsa-kernel/sound/soc/pxa/pxa2xx-pcm.c 2007-01-05
18:10:47.000000000 -0800
@@ -227,6 +227,11 @@ static int pxa2xx_pcm_open(struct snd_pc
if (ret)
goto out;
+ ret = snd_pcm_hw_constraint_integer(runtime,
+ SNDRV_PCM_HW_PARAM_PERIODS);
+ if (ret < 0)
+ goto out;
+
prtd = kzalloc(sizeof(struct pxa2xx_runtime_data), GFP_KERNEL);
if (prtd == NULL) {
ret = -ENOMEM;
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