Re: [Discuss-gnuradio] Synchronizing N210 TX and RX channels

[Stefan Wunsch]

Hey,

If you use the Echotimer you can use the same IP vor TX and RX, this
should work.

Probably you can do your own USRP Sink/Source with UHD. You dont need
much code to implement this (Echotimer ~300 lines in the *impl.cc). Main
change should be an other stream command (most likely
STREAM_MODE_START_CONTINUOUS [0]). Good code examples are UHD
Sink/Source in gr-uhd and especially the examples from UHD itself (<uhd
repo>/host/examples). And the Echotimer of course!

My approach: Read the system time on the USRP, set the stream command on
actual_time+some_offset and spawn two threads with a tx_streamer and a
rx_streamer. You can use both of them on the sampe USRP without any
problems (just dont use two of the same type on one USRP). This should
also work with streaming if you can push your data in the work function
continuously.

Greetings,
Stefan

[0]
http://files.ettus.com/uhd_docs/doxygen/html/structuhd_1_1stream__cmd__t.html#a4df1f2e22148b7e09ace0eca0dfbf904

Am 22.07.2014 19:25, schrieb Daniele Nicolodi:
> Hello Stephan,
> 
> thank for your reply.  What I would like to do is more simple than that:
> I need to synchronize tx and rx of the same USRP, not of two different
> devices.  But I need continuous streaming and not burst.
> 
> Any help in this direction is much appreciated.
> 
> Thanks. Best,
> Daniele
> 
> 
> On 22/07/2014 19:14, Stefan Wunsch wrote:
>> Hey Daniele,
>>
>> I have done the radar toolbox and implemented a synced USRP interface
>> (USRP Echotimer).
>>
>> You are right, the USRP Echotimer does align the timestamps of the TX/RX
>> commands on both USRPs. But if you connect them by MIMO, the time and
>> clock are pretty good in sync. Therefore I think the Echotimer can
>> provide a sync with an accuracy of at least +- 1 sample. Check out [0]
>> for a video of the sync. There is also a sync setup for testing
>> (gr-radar/examples/usrp). Unfortunately the documentation is not
>> finished yet.
>>
>> But care: The Echotimer bursts only a packet in sync, it does not stream
>> the whole time! The packet is defined by a tagged stream.
>>
>> Greetings,
>> Stefan
>>
>> [0]
>> https://grradar.wordpress.com/2014/06/17/synchronisation-echotimer-usrp-interface/
>>
>> Am 22.07.2014 18:40, schrieb Daniele Nicolodi:
>>> On 22/07/2014 18:18, Martin Braun wrote:
>>>> On top of what Marcus' has said,
>>>>
>>>> the gr-radar toolbox might be helpful. It has a block that takes a
>>>> tagged stream, and outputs a signal it acquired synchronously to the
>>>> transmitted one.
>>>
>>> Thanks Martin.  This seems to imply that there is no way to actually
>>> synchronize the hardware, and that the synchronization can only be done
>>> in software aligning the timestamps of the two streams. Is that the case?
>>>
>>> Thanks. Cheers,
>>> Daniele
>>>
>>>
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