Hi Derek,
Thank you very much for your detailed response. I thought that tag's
insertion could be done directly from GRC. I hoped that there would be
some library to insert these tags in a stream. The truth is that I
don't have enough knowledge to write my own block.
On the other hand, I think my problem (which is essentially a burst
stream synchronized with a trigger signal) is conceptually very simple
and must have been encountered by many more people before. I've
searched the whole forum and it's not like that. I am also surprised
that no one else has answered my question.
Regards,
José
Hi Jose,
You'll have to write a block to add those tags where you want them
in the stream (at the start of each burst) and with the time you
want them at (the time is relative to the USRP's internal timekeeper
clock). You'll also need to read from or set the time on that clock
at the start of the application.
The first part you can do with an embedded Python Block to add those
tags. The second part you'll either need to modify the generated
Python flowgraph or use the very latest 3.9 development code which
added the Python Snippets block.
https://github.com/gnuradio/gnuradio/pull/3169
Ettus Research's UHD manual includes a helpful page on
synchronization and how to read/set the time.
https://files.ettus.com/manual/page_sync.html
Regards,
Derek
On 27/02/2020 19:33, jnu...@uvigo.es wrote:
Has anyone worked with tx_time tags?
jnu...@uvigo.es escribió:
Hi, all!
I am working on a proof of concept of a radar system for my
doctoral thesis. I recently installed the great gr-pdu and
gr-timing utilities from Sandia Labs and I am trying to develop a
little application with GNURadio Companion (GRC), based on a USRP
N200 system.
I essentially want to use the rising edges of a pulsed signal to
generate another signal. For this purpose, first the trigger
signal is sampled with a USRP-Source block, then is threshold
detected by means of a "Threshold trigger" block and finally, a
message with a "Tag message trigger" block is generated. The
output of this last block feeds a "PDU to Bursts" block which
enters a USRP-Sink.
I have checked with a "Tag Debug" that the threshold detection and
message generation are both working fine. At the output of the
"PDU to Bursts" block, each burst is tagged with the "tx_sob" and
"tx_eob" tags. The problem arises when those burts enter the
USRP-Sink. As far as I've read, this blocks transmits all burts
sequentially ignoring the time separation that should be between
them. Please, take into account that the trigger pulses are not
equally separated in time, so I must transmit one burst with each
received pulse.
I think the issue is that no "tx_time" tags are being generated
and added to each burst. I wonder if anyone have the same
explanation for this issue, and hopefully, if anyone can guide me
on how can I inject those "tx_time" tags properly in my stream
with GRC.
Any help will be appreciated!
Regards,
José
