Hello everyone

We have been wondering about rx_time tags after drop. In [1] it is stated
that "Then, if a dropped
packet or overflow are detected, it sends a new rx_time tag."

The tag debugger output is shown below.
Initially we thought that in the tag the time and the offset are bound
together. Instead seems that this is true only for the first tag. Meaning,
the offset is always bound to the initial rx_time, as one can see from the
example printout. Both the offset and the time increase (sampling rate is
10e6).

Actually, now that I look at them the rx_time values are messed up, they
are not even monotonically increasing (the timestamp in the second tag is
"newer" than in the third). So what does the rx_time in the tag after drop
represent?

In any case, isn't this a bit counter intuitive? I know we fell for it at
first. There might be more places in the code that mishandle the rx_time
tags after drops. I understand that drops should be avoided, but still I
think it is crucial that they are correctly handled.

---------------------------------------------------------------------
Tag Debug:
Input Stream: 00
  Offset: 0  Source: gr uhd usrp source1     Key: rx_time   Value:
{1480518095 0.75052}
  Offset: 0  Source: gr uhd usrp source1     Key: rx_rate   Value: 1e+07
  Offset: 0  Source: gr uhd usrp source1     Key: rx_freq   Value: 1.56e+08
----------------------------------------------------------------------
D
----------------------------------------------------------------------
Tag Debug:
Input Stream: 00
  Offset: 17461752  Source: gr uhd usrp source1     Key: rx_time Value:
{1480518097 0.497203}
  Offset: 17461752  Source: gr uhd usrp source1     Key: rx_rate Value:
1e+07
  Offset: 17461752  Source: gr uhd usrp source1     Key: rx_freq Value:
1.56e+08
----------------------------------------------------------------------
D
----------------------------------------------------------------------
Tag Debug:
Input Stream: 00
  Offset: 17471916  Source: gr uhd usrp source1     Key: rx_time Value:
{1480518097 0.496695}
  Offset: 17471916  Source: gr uhd usrp source1     Key: rx_rate Value:
1e+07
  Offset: 17471916  Source: gr uhd usrp source1     Key: rx_freq Value:
1.56e+08
----------------------------------------------------------------------
D
----------------------------------------------------------------------
Tag Debug:
Input Stream: 00
  Offset: 17476998  Source: gr uhd usrp source1     Key: rx_time Value:
{1480518097 0.498219}
  Offset: 17476998  Source: gr uhd usrp source1     Key: rx_rate Value:
1e+07
  Offset: 17476998  Source: gr uhd usrp source1     Key: rx_freq Value:
1.56e+08
----------------------------------------------------------------------

With regards
Meelis

[1]
http://gnuradio.4.n7.nabble.com/How-to-get-multipe-rx-time-tags-while-receiving-continuously-tt44492.html#a44515
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