21 Oct
2008
21 Oct
'08
10:22 a.m.
Hello everyone!
I have a couple of questions regarding this.
1. Does every soundcard have a clock?
2. Do other architectures than ALSA offer access to this clock?
3. Can the soundcard clock probably be accessed via simple device file access?
I have looked into OSS, but didn't find anything there, directly reffering
to clocks.
If OSS or other unix sound drivers don't offer access to this resource, how
would they take care of accuracy?
Kindest regards and thanks in advance for any good advise
Julien
--------
Music was my first love and it will be my last (John Miles)
======== FIND MY WEB-PROJECT AT: ========
http://ltsb.sourceforge.net
the Linux TextBased Studio guide
======= AND MY PERSONAL PAGES AT: =======
http://www.juliencoder.de
21 Oct
21 Oct
11:11 a.m.
Hi Julien,
On Tue, Oct 21, 2008 at 4:22 PM, Julien Claassen <julien(a)c-lab.de> wrote:
1. Does every soundcard have a clock?
Yes, if
under clock we understand a device to measure time intervals.
Because digital audio is a stream of samples every of which represents
a strictly defined time interval.
So every sound card has a clock (used to output samples) and produces
a tick (an interrupt) at least on every buffer boundary.
2. Do other architectures than ALSA offer access to
this clock?
3. Can the soundcard clock probably be accessed via simple device file access?
I have looked into OSS, but didn't find anything there, directly reffering
to clocks.
If OSS or other unix sound drivers don't offer access to this resource, how
would they take care of accuracy?
Frankly speaking, I don't know about ALSA
clock API, but given the
"definition" above,
every audio api (callback-based, at least) does provide an implicit
access to the clock.
So you can measure time intervals with an audio clock, but the
accuracy will be limited
by the buffer size and sampling frequency.
Jack uses audio clock exactly this way, and maps this audio clock to system one
with the use of DLL (delay locked loop).
Sorry, if I didn't asked your question directly.
Regards,
Dmitry.
11:34 a.m.
Hello Dmitry!
Thanks! This sounds relatively good for a start. but what I really meant was
a timer derived from the soundcard "clock". ALSA offers an API for the timer.
does anyone know if they really derive tat timer from the soundcard?
2. If some application already uses audio, is there a way for another app to
at least listen for those regularly triggered interupts?
About JACK: Does the JACK api offer a function to use the audio clock info?
Kindest regards
Julien
--------
Music was my first love and it will be my last (John Miles)
======== FIND MY WEB-PROJECT AT: ========
http://ltsb.sourceforge.net
the Linux TextBased Studio guide
======= AND MY PERSONAL PAGES AT: =======
http://www.juliencoder.de
1:41 p.m.
On Tue, Oct 21, 2008 at 5:34 PM, Julien Claassen <julien(a)c-lab.de> wrote:
was a timer derived from the soundcard
"clock". ALSA offers an API for the
timer. does anyone know if they really derive tat timer from the soundcard?
Possibly, but better ask some ALSA guru.
2. If some application already uses audio, is there a
way for another app
to at least listen for those regularly triggered interupts?
You will need some kind
of a daemon that will have a DLL and will
provide the data via shared memory.
In fact JACK does exactly this.
About JACK: Does the JACK api offer a function to use
the audio clock info?
jack_get_time(), jack_time_to_frames() and
jack_frames_to_time()
they to map nframes and jack's time, but the only portable way to map
this to system time
is to use another DLL.
Maybe ALSA timer API is possibly what you really want.
Best,
Dmitry.
5873
days inactive
5873
days old
linux-audio-dev@lists.linuxaudio.org
3 comments
2 participants
participants (2)
-
Dmitry Baikov -
Julien Claassen