Re: [Discuss-gnuradio] Higher Accuracy Metadata Header?

Are you sure you're setting the device time correctly? 2.5ms offset is definitely much much worse than what to devices that should have the same device time should exhibit. So:
How are you setting the device time?

Best regards,
Marcus

On 04/21/2016 08:59 PM, Michael Skaggs wrote:

Aha! You were correct. I was parsing the header incorrectly. However, even after parsing, and the more accurate values (now accurate to 10e-6), it appears the recorded RF data sets are still are offset from each other by an amount of nearly 2.5e-3 seconds. Any idea why this would be? It's strange, especially considering that the are synchronized to the same PPS, and I think the time is with reference to the pulse.

Michael

Michael Skaggs
M.S. - Computer Engineering

LinkedIn | Resume | Research Cluster

University of Maryland, Baltimore County

On Thu, Apr 21, 2016 at 11:57 AM, Marcus D. Leech <mleech@ripnet.com> wrote:

On 04/21/2016 11:41 AM, Michael Skaggs wrote:

I'm trying to time/sample synchronize RF recordings with two B200minis. I am using the detached Metadata File Sink in GRC. Both recordings are at 30MSps and both B200mini boards are synchronized to the same 1PPS signal.

My issue is this, when I extract the data from the Metadata header file, the "rx_time" value is only accurate to 10e-4 seconds (0.0001s). Which, with a recording at 30MSps, this will only give me a sample alignment accuracy to 10e-4(s)*30(MS/s) = 30,000 samples.

If I'm attempting to align the two recordings by samples or time, this is not nearly accurate enough. Is there a way that I can get more accuracy out of my metadata header or a way that I can synchronize the recordings of these B200minis?

Thanks,
Michael

The precision of the timestamps from UHD should have a precision of whatever the master-clock is on the device--how are you interpreting
  the rx_time tag?  It's two parts--a uint64 with the full-seconds portion, and a double-precision float for the fractional part.



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