Re: Inject "tx_time" tags in a stream

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, jnunez@uvigo.es wrote:
>> Has anyone worked with tx_time tags?
>>
>> jnunez@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
>>
>>
>>