[alsa-devel] Input/output error while playing a file using aplay

Pharaoh . pharaoh137 at gmail.com
Tue Jun 26 12:51:05 CEST 2007

>It would really help if you'd show us the code of the version of the
>driver that you're currently talking about.

Hi Clemens...

I had sent you the source file having pcm callbacks yesterday, now I
have modified the pointer function as follows, I am just giving the
pointer function here to avoid duplication, but please let me know in
case you want to have look at the entire file.

static snd_pcm_uframes_t snd_omap_alsa_pointer(snd_pcm_substream_t *substream)

        struct omap_eac *chip = snd_pcm_substream_chip(substream);
        snd_pcm_uframes_t pos = 0;

        pos = audio_get_dma_pos(&chip->s[substream->pstr->stream]);
        printk("Returning pos = %d\n", pos);
        return pos;

static snd_pcm_uframes_t audio_get_dma_pos(struct audio_stream *s)
        snd_pcm_substream_t *substream = s->stream;
        snd_pcm_runtime_t *runtime = substream->runtime;
        unsigned long flags;
        dma_addr_t count;
        unsigned long offset;
        dma_addr_t src,dest;

         if (substream->stream == SNDRV_PCM_STREAM_CAPTURE) {
                dest = omap_get_dma_dst_pos(s->lch[s->dma_q_head]);
                offset = dest - runtime->dma_addr;
                printk("dest is %u and offset is %u\n",dest,offset);
         } else {
                src = omap_get_dma_src_pos(s->lch[s->dma_q_head]);
                offset = src - runtime->dma_addr;
                printk("src is %u and offset is %u\n",dest,offset);

        return bytes_to_frames(substream->runtime, offset);

And the log is as follows.

For the first time.

snd_omap_alsa_pointer start
src is 3246792928 and offset is 3304194048
Returning pos = 20742144
Inside snd_pcm_update_hw_ptr_pos, pos is 20742144
ALSA sound/core/pcm_lib.c:167: BUG: stream = 0, pos = 0x13c8000,
buffer size = 0x4000, period size = 0x800
returning pos 20742144

I can see things are horribaly wrong here....

On 6/26/07, Clemens Ladisch <cladisch at fastmail.net> wrote:
> Pharaoh . wrote:
> > After rewriting the pointer function
> It would really help if you'd show us the code of the version of the
> driver that you're currently talking about.
> > I am not getting the input/output error but I am getting underruns.
> > ...
> > ALSA sound/core/pcm_lib.c:167: BUG: stream = 0, pos = 0x1150000, buffer
> size = 0x4000, period size = 0x800
> Here, "pos" is the value returned by your pointer callback.  This value
> should have been a frame number somewhere in the buffer, i.e., in the
> range 0..0x3fff.  Apparently, the pointer callback doesn't correctly
> calculate this value.
> Please remove most printk()s, and add some in the pointer callback to
> show both the value that you get from the DMA controller, and the value
> that this function returns.
> Regards,
> Clemens

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