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Re: [Discuss-gnuradio] How to pass time tag into usrp sink as a paramete

From: Marcus Müller
Subject: Re: [Discuss-gnuradio] How to pass time tag into usrp sink as a parameter ?[hurry...]
Date: Tue, 16 Dec 2014 17:34:31 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0

Hello Rui,

why do you take the detour through a file? That looks unnecessary.

the USRP sink understands transmission times you specify using tags [1],
so this will be the easiest way to deal with this. You just need to
write a really short block (in C++ or python, whatever you prefer) which
takes the rx_time tag that the USRP source added to the sample stream
and generates a tag with the desired point in time [2].

There are some examples of the rx_time and tx_time tags usage in gr-uhd,
so just search for "tx_time" or "rx_time" in gnuradio/gr-uhd/examples/ .


[1] http://gnuradio.org/doc/doxygen/page_stream_tags.html
[2] http://gnuradio.org/doc/doxygen/page_stream_tags.html
On 12/16/2014 05:21 PM, Rui Zou wrote:
> Hello,
> I would like to implement the process as follows at the Rx side:
> Record the time when the first sample arrived, and then wait for a
> certain interval and then send ack back to Tx. Meanwhile, finish the
> cfo calculating and compensating.
> Here is my whole flow graph design. (Each means a block)
>                            pkt_dtc-> cfo_calc -> file_sink
>                                             cfo_calc -> cfo_cpst
>                                        file_source -> cfo_cpst ->
> usrp_sink
> where pkt_dtc, grab_time_tag and cfo_calc was done myself with C++.
> However, My question are:
> 1. Is it correct of my whole desgin (I want to implement them in one
> top block) or are there any easier solutions ?
> 2. After the block grab_time_tag, how should I pass the time
> information (directly got from the method get_tags_in_range) into the
> usrp_sink as a parameter so as to send ack at the intended time?
> Should I write in Python(but they are not the same level) or C++(but I
> can't rewrite a usrp_sink) ?
> Any doubts or suggestions are highly appreciated !
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