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Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples
From: |
LD Zhang |
Subject: |
Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time? |
Date: |
Fri, 4 Jan 2013 11:21:37 -0800 |
Great! Thanks Josh for the answers to my last email. Please see my comments
and questions below.
============================================================================
========
If you want to use the PC clock, I recommend calling set time now with the
current PC time before scheduling streaming. This will make the USRP tick
counter roughly match the PC clock.
python:
usrp_source.set_time_now(uhd.time_spec_t(time.time())
c++
usrp_source->set_time_now(uhd::time_spec_t(secs, micros, long(1e6));
This way, your only time-ambiguity is the variance in ethernet control
packets and the difference in time between the different PCs. That should
satisfy referenced to PC's time anyway...
>>>
I will try it in Python to set the USRP time. My generated top_block.py is
doing as: self.uhd_usrp_source_0.set_.......
I suppose I will just do:
self.uhd_usrp_source_0.set_time_now(uhd.time_spec_t(time.time())
There is however a question of how often one needs to set the USRP time. It
would depend on how fast the USRP clock drifts with respect to host computer
system time. I remember a number of 2 ppm accuracy of the TCXO frequency
reference. How does this translate to rate of clock drift (in say
micro-seconds drift per hour)?
>>>
--------------------------------------
The next step would be to schedule when a stream begins for each device so
they send RX samples to the host at the "same time" (according to the USRP
anyway).
I think the USRP source block supports setting the time, and streaming at a
specific time, but there isnt a way to do this at the GRC level. So you
might need some hand coded python added to the generated flowgraph, if you
are using GRC.
>>>
OK, I want to do this. But what is the command to do in python? Something
like:
self.uhd_usrp_source_0.rx_sample_time??? Or .schedule_time???
I do need to pass the sample gather start time as a variable to the
top_block.py script. How do I do that (I am a matlaber who is still clumsy
with python)?
Thanks and Regards,
LD
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- [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?, LD Zhang, 2013/01/04
- Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?, John Malsbury, 2013/01/04
- Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?, LD Zhang, 2013/01/04
- Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?, Josh Blum, 2013/01/04
- Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?,
LD Zhang <=
- Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?, Josh Blum, 2013/01/04
- Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?, LD Zhang, 2013/01/04
- Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?, Josh Blum, 2013/01/04
- Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?, LD Zhang, 2013/01/04
- Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?, LD Zhang, 2013/01/04
- Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?, Marcus D. Leech, 2013/01/04
- Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?, LD Zhang, 2013/01/04
- Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?, LD Zhang, 2013/01/07
- Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?, Josh Blum, 2013/01/07
- Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?, Marcus D. Leech, 2013/01/07