[alsa-devel] new driver: 30mS interval problem

[Takashi Iwai]

At Tue, 26 Feb 2008 13:56:51 +0100,
William Juul wrote:
> 
> On Mon, Feb 25, 2008 at 4:43 PM, Takashi Iwai <tiwai at suse.de> wrote:
> > At Mon, 25 Feb 2008 15:46:28 +0100,
> >
> > William Juul wrote:
> >  >
> >  > Hello
> >  >
> >  > I am new to ALSA and trying to write a new driver for a DAC connected
> >  > with PCM to an AVR32 on a NGW100 reference card provided by Atmel.
> >  >
> >  > The sampling rate I am currently using is 11047and the DAC is
> >  > providing 4 channels of 24bit. The HW interface is using DMA to copy
> >  > data to RAM.
> >  > By studying the audio data in hexdump or in Audacity I can verify that
> >  > the sound looks good in intervals of about 30mS, then all channels are
> >  > garbled for 30mS. This pattern repeat itself throughout the audio
> >  > capture.
> >  >
> >  > I am not confident I have configured all ALSA parameters properly.
> >  > How can I go about fixing/debugging this 30mS intverval problem?
> >
> >  Maybe the period size has to be aligned to some value?
> >
> >
> >  >
> >  > Below is the command I am using.
> >  >
> >  >
> >  > Best regards
> >  > William Juul
> >  >
> >  > # arecord -r 11047 -c 4 -f S24_LE -s 1 -A 100 -d 5 --buffer-size 16384
> >  > -F 21333 -v > test.wav
> >
> >  Try to change the period size as well.
> >
> >
> >  Takashi
> >
> I tried changing the period size in both directions but it would never
> change to anything but 490.

Then your driver has some constraints.  Or does it use dmix?

> Then I tried changing the number of channels. -c 1 gave me lots of
> "overrun", but -c 2 made everything work. The WAV file would still
> contain data from all 4 channels. I do not understand the correlation
> between the different parameters and why it behaves like this. Thus I
> do not know what to adjust to remedy this.
> 
> The command I used to make everything work was:
> arecord -r 11047 -c 2 -f S24_LE -s 100 -A 10000 -d 5 > test.wav
> 
> It turned out that --buffer-size and -F did not actually change anything.

Check with -v option what plugins are being used.


Takashi