[Discuss-gnuradio] not getting timestamps from UHD received stream tags

[George Nychis]

I am trying to read incoming RX timestamps from the UHD sample stream.  I'd like to calculate the approximate time a preamble is received in the OFDM code.

The issue is that, despite getting incoming frames and preambles, I do not seem to be getting timestamp values.  I use get_tags_in_range() on "rx_time":

https://github.com/gnychis/grforwarder/blob/8f8c4e6cf79a2d635a0eb3bcad9b5ab325f1e373/gr-digital/lib/digital_ofdm_sampler.cc#L78

However, the size of the rx_time tags is consistently zero:

https://github.com/gnychis/grforwarder/blob/8f8c4e6cf79a2d635a0eb3bcad9b5ab325f1e373/gr-digital/lib/digital_ofdm_sampler.cc#L99

The output of the OFDM receiver code:

ok: True         pktno: 637      n_rcvd: 18      n_right: 17

got a preamble, size of time_tags: 0

ok: True         pktno: 638      n_rcvd: 19      n_right: 18

got a preamble, size of time_tags: 0

ok: True         pktno: 639      n_rcvd: 20      n_right: 19

got a preamble, size of time_tags: 0

...

Is there something I am missing to enable the RX timestamp on the incoming samples, or am I not properly reading the stream tag?  My branch came from the GR master 4 days ago (309ca769af).  

Thanks a bunch.

- George