resetting buffer on /dev/dsp

[Andrew Collier]

hello,

i am maintaining a system for acquiring very low frequency radio
waves. we have a receiver hooked up to the sound card. this system is
presently running at the south african base in antarctica. i have the
following question: is it possible to reset the kernel input buffer on
/dev/dsp? the reason i am concerned about this is that accurate timing
is critical for our data. presently the system gets a time stamp and
then starts reading from /dev/dsp. however, there is data present in
the buffer which was read from the sound card at some time prior to
getting the time stamp and this introduces a lag between the nominal
sample time and the actual sample time.

what i failed to mention was that the code is written in c for a linux
platform. i have tried both of:

ioctl(sndinit::devdspfd, SOUND_PCM_SYNC, 0);

and

ioctl(sndinit::devdspfd, SOUND_PCM_RESET, 0);

but neither has the desired effect. this is probably due to a large
dose of ignorance on my part!

what i am basically wanting is a way to make the kernel restart
filling its internal buffer from the beginning (_discarding_ any data
present in the buffer at that time).

any ideas?

best regards,
andrew collier.

[Jan Engelhardt]

>hello,

i am maintaining a system for acquiring very low frequency radio ....
what i failed to mention was that the code is written in c for a linux
platform. i have tried both of:

ioctl(sndinit::devdspfd, SOUND_PCM_SYNC, 0); Uh, looks like C++.
and
ioctl(sndinit::devdspfd, SOUND_PCM_RESET, 0);
Those ioctl()s may not be implemented for your soundcard. Try checking their
return status, or, see what they do in the kernel sources.
SOUND_PCM_RESET might only reset the DAC/ADC controller, leaving the kernel
buffers untouched.
what i am basically wanting is a way to make the kernel restart
filling its internal buffer from the beginning (_discarding_ any data
present in the buffer at that time).
any ideas?

If there is no worldwide available solution, you might try modifying the linux
kernel a bit to suit your needs.

--
- Jan Engelhardt

[Andrew Collier]

> >ioctl(sndinit::devdspfd, SOUND_PCM_SYNC, 0);

Uh, looks like C++.

okay, you got me there!

[Kevin Easton]

In comp.lang.c Andrew Collier <ab*******@phreaker.net> wrote:

hello,

i am maintaining a system for acquiring very low frequency radio
waves. we have a receiver hooked up to the sound card. this system is
presently running at the south african base in antarctica. i have the
following question: is it possible to reset the kernel input buffer on
/dev/dsp? the reason i am concerned about this is that accurate timing
is critical for our data. presently the system gets a time stamp and
then starts reading from /dev/dsp. however, there is data present in
the buffer which was read from the sound card at some time prior to
getting the time stamp and this introduces a lag between the nominal
sample time and the actual sample time.

You might want to try asking in comp.os.linux.development.system and/or
comp.os.linux.development.apps.

- Kevin.