[alsa-devel] reset of kernel input buffer for /dev/dsp

[Takashi Iwai]

At Mon, 29 Nov 2010 17:40:03 +0900,
Amit Nagal wrote:
> 
> Hi ,
> 
> Thanx for the reply .
> 
> we tried SNDCTL_DSP_RESET , but it is not flushing  the kernel pcm
> buffer for us  .

It should.  It abandons the pending data and resets to the initial
state before starting the stream.

But, it might be a bug in OSS emulation later.  It doesn't seem to
reset the internal buffer.  Try the patch below.

> any other method which we can use ?

> also please lets us the function available with alsa - lib which
> serves the purpose of flushing
> the kernel pcm buffer .

snd_pcm_drop() corresponds to it.


Takashi

---
diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
index 5c8c7df..a4411a3 100644
--- a/sound/core/oss/pcm_oss.c
+++ b/sound/core/oss/pcm_oss.c
@@ -1510,16 +1510,19 @@ static ssize_t snd_pcm_oss_read1(struct snd_pcm_substream *substream, char __use
 static int snd_pcm_oss_reset(struct snd_pcm_oss_file *pcm_oss_file)
 {
 	struct snd_pcm_substream *substream;
+	struct snd_pcm_runtime *runtime;
+	int i;
 
-	substream = pcm_oss_file->streams[SNDRV_PCM_STREAM_PLAYBACK];
-	if (substream != NULL) {
-		snd_pcm_kernel_ioctl(substream, SNDRV_PCM_IOCTL_DROP, NULL);
-		substream->runtime->oss.prepare = 1;
-	}
-	substream = pcm_oss_file->streams[SNDRV_PCM_STREAM_CAPTURE];
-	if (substream != NULL) {
+	for (i = 0; i < 2; i++) { 
+		substream = pcm_oss_file->streams[i];
+		if (!substream)
+			continue;
+		runtime = substream->runtine;
 		snd_pcm_kernel_ioctl(substream, SNDRV_PCM_IOCTL_DROP, NULL);
-		substream->runtime->oss.prepare = 1;
+		runtime->oss.prepare = 1;
+		runtime->oss.buffer_used = 0;
+		runtime->oss.prev_hw_ptr_period = 0;
+		runtime->oss.period_ptr = 0;
 	}
 	return 0;
 }