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From: | Lapointe, Benjamin - 1008 - MITLL |
Subject: | Re: [Discuss-gnuradio] [USRP-users] sample time alignment in GRC |
Date: | Thu, 19 Jun 2014 16:39:55 +0000 |
Nicholas, Thanks for your message, I implemented your changes to my top_block.py file, but was unable to get the two data streams from the X310s to start sampling at
the same time. I verified with the print statements that python was doing the time conversions and math correctly.
I used a WX Scope Sinc and analyzed recorded data in MATLAB to look at time offsets in the two data streams. I also set the 1 second waits to 2 second waits.
I generally saw time offsets in the range of 5 to 25 samples (1 to 5 usec with 5MHz output), and one occurrence of ~200 sample offset between the two sample streams. Nicholas, how did you verify sample time alignment? I attached my top_block python file, in case anyone has time to look at it.
Any other ideas/comments? Thanks! -Ben From: Linnenkamp, Nicholas [mailto:address@hidden
Ben/Rob, I addressed the issue of getting time aligned samples going for USRP devices sometime back. I had similar issues until I did a deep dive and worked out some
of the problems. There is a bit more to the process than just setting sync and reference sources. http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/2014-April/009277.html That contains code for getting gnu-radio to perform the required initialization for the devices so that they sample at the same time. Perhaps someone from
the gnuradio camp can figure out how to do it automagically. Nicholas From: USRP-users [mailto:address@hidden]
On Behalf Of Robert Kossler via USRP-users Hi Ben, I am having a similar (but not identical issue). I have a single X310 for which I am trying to make sure both channels are time aligned. I have tried both the internal PPS signal and an external PPS signal. I noticed channel-to-channel
time delays of 1, 2, or 3 "clock" cycles (at clock rate, not sample rate) which varied from run to run. My measurements were done with a modified "rx_samples_to_file" program and Matlab processing. I have not yet duplicated using GRC. Rob On Tue, Jun 17, 2014 at 9:58 AM, Lapointe, Benjamin - 1008 - MITLL via USRP-users <address@hidden> wrote:
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time_align_test_no_delay.py
Description: time_align_test_no_delay.py
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