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

[Josh Blum]

On 02/06/2012 06:13 PM, George Nychis wrote:
> 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).
> 

The timestamps are only sent on the very first packet and after overflow
conditions. Are you seeing at least one tag at the very beginning of
streaming?

-Josh