[Discuss-gnuradio] trying to create stream tag, pass down, not as expected?

[George Nychis]

I am trying to pass a stream tag down the chain in the OFDM code.  As a point of reference, I am using Tom, Matt, and Bob's figure from their SDR08 paper:

What I want to do is in gr.ofdm_sampler, calculate the clock time the preamble was received at the USRP, then pass it on forward all the way to the python code so that every incoming decoded packet has a timestamp associated with it, which is the time the preamble was received.

So, in gr.ofdm_sampler, I calculate the timestamp and create a new stream tag, putting it on port 1 (note: also tried port 0):

https://github.com/gnychis/grforwarder/blob/7a9d5735b341f5c226b6d3a249f51bf5edfee54f/gr-digital/lib/digital_ofdm_sampler.cc#L153

At this point, I output:

"--- added sync tag in ofdm_sampler\n"

Then, this stream tag should hit gr.ofdm_frame_acquisition.  I do a quick check for it on incoming port 1:

https://github.com/gnychis/grforwarder/blob/7a9d5735b341f5c226b6d3a249f51bf5edfee54f/gr-digital/lib/digital_ofdm_frame_acquisition.cc#L191

And output:

"--- got sync tag in frame_acq\n"

Next, I make the same check in gr.ofdm_frame_sink for my stream tag (at top of work):

https://github.com/gnychis/grforwarder/blob/ade8b55b68115288b88b35a968a79a86966db14e/gr-digital/lib/digital_ofdm_frame_sink.cc#L301

And output:

"--- got sync tag in frame_sink\n"

Finally, I check for the stream tag right before the new gr.message is put in to the queue in gr.ofdm_frame_sink:

https://github.com/gnychis/grforwarder/blob/ade8b55b68115288b88b35a968a79a86966db14e/gr-digital/lib/digital_ofdm_frame_sink.cc#L414

If no stream tag is found, I output:

std::cerr << "---- Header received, with no sync timestamp? (" << nread << ")\n"

Now, what I would expect is that when I get an incoming frame, I go down that set of outputs one by one, and then I get the output that I've received a packet.  But, that doesn't seem to be the case:

http://pastebin.com/hZpuQc12

Instead, I typically get this with no output from frame_acq or frame_sink other than frame_sink to tell me it didn't get the stream tag:

--- added sync tag in ofdm_sampler

---- Header received, with no sync timestamp? (181)

ok: True pktno: 156 n_rcvd: 2 n_right: 1 valid_ts: 0

Then after a little while, I get a dump from frame_acq and frame_sink:

--- added sync tag in ofdm_sampler

---- Header received, with no sync timestamp? (509)

ok: True pktno: 174 n_rcvd: 20 n_right: 19 valid_ts: 0

--- added sync tag in ofdm_sampler

--- got sync tag in frame_acq

--- got sync tag in frame_sink

--- got sync tag in frame_acq

--- got sync tag in frame_sink

--- got sync tag in frame_acq

--- got sync tag in frame_sink

The number of those don't correspond to how many frames that I have received, and at some point just stop showing up:

http://pastebin.com/hZpuQc12 (lines 231 -> 953 have no output from frame_acq or frame_sink)

Am i missing something fundamental about how the stream tag is passed forward?

Thanks!

George