Hello list,
I want to record UTC-timestamped USRP data, and I’ve created a flowgraph using the file meta sink. I set the USRP time via set_time_now (in the final version this will become set_time_next_pps) before the file sink is created, and reading back immediately using get_time_now returns the same time. The files contain all the inline header fields… but the rx_time appears to be consistently 4 times the true value!
Example 1:
USRP time set to 1626425142 seconds after epoch -> 07/16/21 08:45:42
get_time_now returns 1626425142 seconds
In the file header ‘rx_time’ is followed by: 0c 00 00 00 02 0b 00 00 00 01 83 c5 1c d9 04 …
0x0000000183c51cd9 = 6505700569 full secs
Example 2:
USRP time set to 1626439661 seconds after epoch -> 07/16/21 12:47:41
get_time_now returns 1626439661 seconds
File header ‘rx_time’ is followed by: 0c 00 00 00 02 0b 00 00 00 01 83 c5 ff b5 04 …
0x0000000183c5ffb5 = 6505758645 full secs
Example 3:
USRP time set to 100 seconds exactly
get_time_now returns 100 seconds
File header ‘rx_time’ is followed by: 0c 00 00 00 02 0b 00 00 00 00 00 00 01 91 04 …
0x0000000000000191 = 401 full secs
It looks like the fractional seconds part is affected in the same way – inserting, say, a 0.1 sec sleep after setting the USRP time results in approximately 0.4 sec additional delay in rx_time.
Can anyone explain this!? All other header values come out as expected. I’m using Gnuradio version 3.7.13.5 with UHD 3.15.0.
Thanks,
Andy
Andrew Chadwick
Consultant Engineer
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Phone +44 (0)1794 833257
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