Re: [Discuss-gnuradio] clock synchronization by message passing

[Jay Prakash]

I went through the stream tagging pdf.

The tags from source has time,freq and rate.

I am interested in insuring that transmitter sets a particular frequency of transmission ie Tx_Next_freq and time at which the transmitter starts sending data packets at an instance.

The set_command_time as you suggested should work.

I see the features being implemented in Pre-cog.Can I get a heading of how has these two features been insured?

The sole purpose of my questions is setting a synchronized frequency hopping and unbroken data transfer at these hopping channels.

I have a set of TX frequencies [f1,f2,..........fn]

and Receiver two has the knowledge of the frequency table.

Now I have a file and want to send certain chunks at different frequencies and insure Receiver receives them without error.

For this Receiver will have to be synchronized with Tx and hop instances of rx/tx should not be lagging.

Setting time of transmission/freq hop from tx side and getting rx_time info from tags can help in establishing the channel I want.

Please help me figuring out the synchronization with respect to Pre-cog implementation.

Jay Prakash 

On Mon, Jun 17, 2013 at 12:43 AM, John Malsbury <address@hidden> wrote:

"how can i make the usrp send its time when configured for synchronization?"

I might be misunderstanding the question, but here's an answer.  The USRP source outputs stream tags on the first sample when streaming.  The three tags are 1) rx_time 2) rx_rate 3)  frequency.  Using (1) and (2), you should be able to determine and track the time of the USRP.

You would use set_command_time for anything with commands - gpio, tuning, etc.  This is in the control plane. You do timed bursts in the data plane with stream tags -> tx_sob, tx_time, tx_eob.

If these terms are foreign to you, Google "introduction to stream tags" by Tom R.

-John

On Sun, Jun 16, 2013 at 12:02 PM, Jay Prakash <address@hidden> wrote:

I think i can use set_command_time (which i guess set the next time of transmission/command?).

how can i make the usrp send its time when configured for synchronization?

Jay Prakash 

Senior Undergraduate 

Electronics Engineering

IIT (BHU)

VARANASI

+91-9559475258

http://about.me/jay.prakash/

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On Sun, Jun 16, 2013 at 11:58 PM, John Malsbury <address@hidden> wrote:

"XML_RPC block in the new gr-extras"

XML_RPC would have been subject to the same limitations.  It could only call set_time_next_pps if set_time_next_pps was in the uhd_sink/source blocks.  Maybe you can update them to include the function.

Let me ask a more fundamental questions - why do you want to reset the time?

-John

On Sun, Jun 16, 2013 at 11:20 AM, Jay Prakash <address@hidden> wrote:

so do we have any other block to do that. I did'nt find XML_RPC block in the new gr-extras

Jay Prakash 

Senior Undergraduate 

Electronics Engineering

IIT (BHU)

VARANASI

+91-9559475258

http://about.me/jay.prakash/

http://www.linkedin.com/profile/view?id=91120191&trk=hb_tab_pro_top

On Sun, Jun 16, 2013 at 11:43 PM, Adeel Anwar <address@hidden> wrote:

> so i checked the new grextras wiki it has uhd_control block i guess that can be used for this job.

uhd_control block  supports only a subset of usrp-functions (exposed through gr-uhd) e.g. "set_command_time", set/get_gain/freq etc BUT currently it doesn't support "set_time_now()"
https://github.com/guruofquality/grextras/blob/master/lib/uhd_control_port.cpp

-Adeel

On Sun, Jun 16, 2013 at 11:06 AM, Jay Prakash <address@hidden> wrote:

thanks for the clarification

so i checked the new grextras wiki it has uhd_control block i guess that can be used for this job.

Jay Prakash 

Senior Undergraduate 

Electronics Engineering

IIT (BHU)

VARANASI

+91-9559475258

http://about.me/jay.prakash/

http://www.linkedin.com/profile/view?id=91120191&trk=hb_tab_pro_top

On Sun, Jun 16, 2013 at 11:05 PM, John Malsbury <address@hidden> wrote:

The GPSDO can provide an "internal" 10 MHz/1 PPS signal.  I'm not sure if that's what you meant or not:  https://www.ettus.com/product/details/GPSDO-KIT

AFIAK, you cannot set the time of a USRP with a message. You may be able to use the XML_RPC block in gr-extras to call the function if it is exposed through gr-uhd.

-John

On Sun, Jun 16, 2013 at 10:30 AM, Jay Prakash <address@hidden> wrote:

how can we set the time of usrp by sending it message. I know there are function to (usrp.set_time_now()) do this from from top block variable but can this be done by sending message at usrp port . 

We can give internal reference signal of 10MHz  but is there also a way to give pps signal internally i.e. without using any external hardware.

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