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

[Michael Skaggs]

Hey Marcus,

In GRC, I have a USRP Source block with "Sync" set to "Unknown PPS" and "Timing Source" set to "External". I assumed the device would be setting time based on the external PPS using these parameters. The synchronize(S0) LED goes solid (after about half a second of recording, maybe less) and the other LED (S1) is blinking with the PPS.

Thanks,
Michael

On Fri, Apr 22, 2016 at 11:56 AM, Marcus Müller <address@hidden> wrote:

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

On Thu, Apr 21, 2016 at 11:57 AM, Marcus D. Leech <address@hidden> 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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