GR_Soapy, LimeSDR-USB and rx_time timestamping

[Eliz Lesh]

GR_Soapy, LimeSDR-USB and rx_time timestamping

GNU Radio 3.10.5 (Brew)

OSX

LimeSDR-USB

The latest Patch notes indicates GR-Soapy supports UHD style stream tagging.  Connecting the Soapy Source(LimeSDR) to Message Debug, the first packet is tagged with rx_time, rate, and frequency, but no subsequent packets are tagged.  

I have a simple flow graph that monitors a single ~10khz UHF channel for power detection and records start/stop timestamps.

 The flowgraph looks like:

SoapySource(Lime Driver, 2mhz sample rate)—>decimating(10x) FFT Filter—>RMS—>Log10—>Python block.  

Python block checks samples vs threshold and timestamps signal start and signal stop.   Calculating timestamps by counting samples in the python block, it slowly loses time at irregular intervals, presumably due to packet loss.   Is there a way to call the soapy-source(Limesdr) block to send a new tagged packet so I can resync the counter/clocks?  I need to reach timing resolution and accuracy better than system time can deliver.  Any clever ideas or tips on edge detection would be well received.  

Thank you and Happy Holidays,

Elizabeth