[alsa-devel] cmipci and sound skipping ?

[Clemens Ladisch]

Matija Nalis wrote:
> My card is "Asonic C-Media8738, 4 channel" and mostly works with snd_cmipci
> driver - it is just that (even on completely unloaded system) the sound is
> (very annoyingly) skipping.
> ...
> ALSA pcm_lib.c:316: BUG: pcmC0D0p:0, pos = 4294918144, buffer size = 16384, period size = 1024
> 
> Note that the pos is *always* the same (4294918144 = 0xffff4000 = -16384) which might be important.

This looks like a hardware bug.

It's possible that we can get a valid pointer by reading the register
multiple times.  Please try the patch below.


Regards
Clemens


diff --git a/sound/pci/cmipci.c b/sound/pci/cmipci.c
index 1ded64e..8416b8a 100644
--- a/sound/pci/cmipci.c
+++ b/sound/pci/cmipci.c
@@ -941,13 +941,21 @@ static snd_pcm_uframes_t snd_cmipci_pcm_pointer(struct cmipci *cm, struct cmipci
 						struct snd_pcm_substream *substream)
 {
 	size_t ptr;
-	unsigned int reg;
+	unsigned int reg, rem, tries;
+
 	if (!rec->running)
 		return 0;
 #if 1 // this seems better..
 	reg = rec->ch ? CM_REG_CH1_FRAME2 : CM_REG_CH0_FRAME2;
-	ptr = rec->dma_size - (snd_cmipci_read_w(cm, reg) + 1);
-	ptr >>= rec->shift;
+	for (tries = 0; tries < 5; tries++) {
+		rem = snd_cmipci_read_w(cm, reg);
+		if (rem < rec->dma_size)
+			goto ok;
+	} 
+	printk(KERN_ERR "cmipci: invalid PCM pointer: %#x\n", rem);
+	return SNDRV_PCM_POS_XRUN;
+ok:
+	ptr = (rec->dma_size - (rem + 1)) >> rec->shift;
 #else
 	reg = rec->ch ? CM_REG_CH1_FRAME1 : CM_REG_CH0_FRAME1;
 	ptr = snd_cmipci_read(cm, reg) - rec->offset;