Two machines that are only connected through Ethernet should generate an impulse signal at a well defined global time. I want to measure the jitter between the two impulse signals.
For that purpose I have implemented an application with two threads. One thread is finding a mapping between the global time and the audio sample clock (a clock which is directly related to the playout of audio samples, e.g. a counter of currently played samples) by periodically measuring the current sample clock. Therefore an API method such as snd_timer_info_get_ticks(...) or snd_pcm_delay(...) or snd_pcm_status_get_tstamp(...) is needed. The second thread generates an impulse at given sample clock. Therefore it must know, which sample clock corresponds to what offset in the snd_pcm_channel_area_t. How do you think I could achieve that with the given API? Regards, Men PS: I was talking of ADAT synch, because in normal play mode the ADAT synch counts the number of samples currently played out. > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:alsa-devel- > [EMAIL PROTECTED]] On Behalf Of Paul Davis > Sent: Freitag, 15. November 2002 16:03 > To: [EMAIL PROTECTED] > Cc: [EMAIL PROTECTED] > Subject: Re: [Alsa-devel] read time information > > >For synchronization purpose I need the current time of my sound card > >(information on the sample that is currently played out might be > >sufficient / ADAT-Synch timecode) I did anticipate that the functions > > the code to read the ADAT sync timecode is written, but is not > "exported" to a usable part of the ALSA API. it will likely show up as > a readable PCM "control". > > >snd_pcm_hwsynch(...) > > never heard of that function. you learn something new every day :) > > >snd_pcm_delay(...) > > > >must be used to get the current sample positions of the DAC/ADC. But > >these functions do not seem to work on my system (alsa-0.9.0rc5 and an > >RME9652 sound card). Besides that I want to read the ADAT-Synch timecode > >instead of the buffer relative sample offset. > > they are two completely different things. one is not a substitute for > the other. > > >Therefore I was looking for another solution to get the time. I tried to > >use the ALSA timer interface > >(http://www.alsa-project.org/alsa-doc/alsa-lib/_2test_2timer_8c-example . > >html#example_test_timer). But unfortunately I am getting a "timer time > >out!", which means that > > > >snd_timer_poll_descriptors(...) > > > >did fail. Is the timer interface implemented for the By the RME9652? By > >the way I do not understand how the sample number to the read time do > >correlate with each other. > > the "timer" interface is part of the core of the ALSA drivers, its not > specific to any particular driver. i have no idea how to use it > however, and its not documented anywhere except for a few messages in > the archives of this list and/or alsa-user. > > but first you need to define what it is that you are trying to > do. bringing the ADAT sync timecode into the picture greatly confuses > things because this has nothing to do with the other functions you are > describing. ADAT sync time can move backwards, can speed up, slow down > etc. > > >I would appreciate any help with this because if I cannot solve this > >problem, I have to move to Windows ASIO (what a pitty!) ASIO provides > >the functions > > > >ASIOGetSamplePosition(...) > >bufferSwitchTimeInfo(...) > > > >which do exactly what I need. > > and what is it that you need? what are you trying to do? > > --p > > > > ------------------------------------------------------- > This sf.net email is sponsored by: To learn the basics of securing > your web site with SSL, click here to get a FREE TRIAL of a Thawte > Server Certificate: http://www.gothawte.com/rd524.html > _______________________________________________ > Alsa-devel mailing list > [EMAIL PROTECTED] > https://lists.sourceforge.net/lists/listinfo/alsa-devel ------------------------------------------------------- This sf.net email is sponsored by: To learn the basics of securing your web site with SSL, click here to get a FREE TRIAL of a Thawte Server Certificate: http://www.gothawte.com/rd524.html _______________________________________________ Alsa-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/alsa-devel
