Bruce Paterson wrote:
>
I got zero feedback on the problem below, so I thought I'd add the code
segment and see
if anyone can tell me what I'm doing wrong !
See code below.
> HELP !
> I've tried everything I can think of and I'm at a loss.
>
> Setup:
> alsa 0.9.0rc2
> soundcard Terratec EWS88 (ice1712 driver)
> direct hw:0,0 using snd_pcm_readi & writei with descriptor polling.
> length approx 50s similtaneous read & write. read from all channels.
> modified 'envy24setup' to preset hardware levels on startup
> full restart of sound system each 'pass' (new handles etc.)
>
> Problem:
> The first pass works fine with beautiful audio.
> The next pass the output is badly distorted (sounds like an incomplete
> buffer or something), but
> no errors reported, no under/overruns.... only evidence that something
> is wrong is to listen to it.
>
> What fixes it:
> Waiting. Yup...if I wait > 1 minute before the 2nd pass then that is
> also fine. Something 'happens'
> in that time to make it all ok again.
> This is why it's taken me ages to actually notice the problem at all !
> (program has been running
> for months).
>
> What *doesn't* help:
> Not doing a full sound restart between passes (ie. merely doing a drop
> afterwards, then restart with
> prepare & start, leaving pcm handles alive).
> Playing a wav file with 'aplay' in between passes.
> Exiting from my program and starting again between passes.
> adding hw_free commands prior to close of the in & out handles.
Recent observations: The distortion (buffer problem ?) seems to occur a
fixed interval after
the sound is started after a good delay then stopped, then started
again. ie. If I send shorter bursts
I can get two good ones in beofre a bad one (quite consistantly),
whereas only 1 good longer burst.
Also, if I send a really really long burst (ie continueous) the problem
never occurs. It's only if I stop
then start again !
Here is the code segment in question. The periodsize is setup to be 1/4
of the buffersize which is set
to the maximum the soundcard will give me. When restarting the soundcard
is initialised from scratch
(new fd's), but I tried without doing this and it makes no difference):
/* Get one full width buffer, buffersize is in frames. */
outbuf = (char *)calloc(out_buffer_size * OUTCH,
snd_pcm_format_width(format) / 8);
/* calloc since we want silence initially on output */
inbuf = (char *)calloc(in_buffer_size * INCH,
snd_pcm_format_width(format) / 8);
/* Start the ball rolling */
snd_pcm_prepare(outhand);
snd_pcm_prepare(inhand);
snd_pcm_reset(outhand);
snd_pcm_reset(inhand);
snd_pcm_start(inhand);
/* This is the IO loop */
outp = a buffer that contains what I want to output;
outl = length of said buffer;
outs = (QUIET * (Fs/1000)); /* Pre-silence output time */
Delay *= Fs; /* Change to sample count */
Delay += QUIET * (Fs/1000); /* Always delay the output quiet period as
well */
dc = Delay;
samps = N;
ocopy = 0;
/* inptrs already point to fmptrs */
for(;;)
{
if(outs)
out = outs;
else
{
if(outl)
{
if( ocopy == 0 )
{
ocopy = 1;
/* Copy from single channel full buffer to
full width one */
sampl = (long *)outp;
sampm = (long *)outbuf;
for(x=0; x < out_buffer_size; x++)
{
/* only 2 channels output (180 deg out
of phase) */
*sampm = *sampl++;
sampm += OUTCH; /* Skip over
other output channels */
if( x > outl )
break;
}
out = outl;
}
}
else
out = out_buffer_size; /* Silence after */
}
/* See if ready for output data yet */
poll(outfds, ocount, -1);
snd_pcm_poll_descriptors_revents(outhand, outfds, ocount,
&revents);
if (revents & POLLERR)
{
fprintf(stderr, "Tx Poll failed\n");
err = -1;
break;
}
if (revents & POLLOUT)
{
err = snd_pcm_writei(outhand, (void *)outbuf, out >
out_buffer_size ?
out_buffer_size : out );
if( err < 0 )
{
/* EAGAIN Shouldn't happen now since we're polling
first */
if( err != -EAGAIN )
{
fprintf(stderr, "Write failed %s",
snd_strerror(err));
break;
}
}
else
{
if(outs)
outs -= err;
else
{
if(outl)
{
outl -= err;
outp += err *
snd_pcm_format_width(format)/8;
ocopy = 0;
if( outl == 0 )
{
/* Finished actual output. Now
fill buffer with silence again */
sampm = (long *)outbuf;
for(x=0; x < out_buffer_size;
x++)
{
*sampm++ = 0;
*sampm = 0;
sampm += OUTCH-1; /*
Skip over other output channels */
}
}
}
}
}
}
/* See if data ready to be read yet... we started sampling earlier. */
poll(infds, icount, -1);
snd_pcm_poll_descriptors_revents(inhand, infds, icount,
&revents);
if (revents & POLLERR)
{
fprintf(stderr, "Rx Poll failed\n");
err = -1;
break;
}
if( !((revents & POLLIN) || (revents & POLLPRI)) )
continue;
if(dc)
{
err = snd_pcm_readi(inhand, inbuf, dc > in_buffer_size ?
in_buffer_size : dc);
if(err < 0)
{
if( err != -EAGAIN )
{
fprintf(stderr,"Read error at %ld: %s\n",
Delay-dc,
snd_strerror(err));
break;
}
}
else
{
dc -= err;
if( dc )
continue;
}
}
/* Finally actually record some real stuff */
err = snd_pcm_readi(inhand, inbuf, samps > in_buffer_size ?
in_buffer_size : samps);
if(err < 0)
{
if( err != -EAGAIN )
{
/* No point in underrun recovery in this application
so abort */
fprintf(stderr,"Read error at %ld: %s\n", N-samps,
snd_strerror(err));
break;
}
}
else
{
samps -= err;
/* Copy from full width buffer to channels */
for(y=0; y < channels; y++)
{
sampl = (long *)inbuf + y;
sampm = (long *)inptrs[y];
for(x=0; x < err; x++)
{
*sampm++ = *sampl;
sampl += INCH;
}
inptrs[y] += err * snd_pcm_format_width(format)/8;
}
if( samps <= 0 )
break;
}
}
fprintf(stderr,"Sampling Completed\n");
snd_pcm_unlink(outhand);
snd_pcm_drop(outhand);
snd_pcm_drop(inhand);
snd_pcm_hw_free(outhand);
snd_pcm_close(outhand);
snd_pcm_hw_free(inhand);
snd_pcm_close(inhand);
/* Free up temporary memory */
free(inbuf); free(outbuf);
--
Cheers,
Bruce
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/\\\/\\\/\\\ / / Bruce Paterson
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/ /\\\/\\\/\\\/ / 87 Peters Ave, Mulgrave, Vic, 3170
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