Re: Inject "tx_time" tags in a stream

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
>
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