[USRP-users] TwinRX tuning timing

Marcus D. Leech mleech at ripnet.com
Fri Jul 14 16:46:00 EDT 2017


On 07/14/2017 04:22 PM, Eugene Grayver wrote:
>
> Yes, I definitely agree that there’s no way to tell when the tuning is 
> DONE.  However, my question was about the ‘shortly after’ part.  
> Should it not be inserted ‘shortly before’, or ‘exactly at’?  Since 
> there’s typically no way to look into the future, (yes, of course it 
> is doable), there’s no way for somebody to know that the samples that 
> are before the tag are actually ‘invalid.’
>
> _______________________
> Eugene Grayver, Ph.D.
> Aerospace Corp., Sr. Eng. Spec.
> Tel: 310.336.1274
> ________________________
>
The control-plane an data-plane run asynchronously to one another. The 
only guarantee is that samples that arrive after the tag will be after 
the comman has been issued.


> *From:*mleech at ripnet.com [mailto:mleech at ripnet.com]
> *Sent:* Friday, July 14, 2017 12:34 PM
> *To:* Eugene Grayver <eugene.grayver at aero.org>
> *Cc:* usrp-users at lists.ettus.com
> *Subject:* Re: [USRP-users] TwinRX tuning timing
>
> The frequency tag is inserted at some point shortly after the 
> command-set is issued to the hardware.  There's no way for the various 
> bits and pieces to tell when the underlying (mostly analog) hardware 
> has converged to an "acceptable" steady-state operating mode.  PLL 
> synthesizers don't instantly switch from one frequency to another, 
> digital (and analog) filters have group delays, etc.
>
> The time to achieve steady-state can vary from hardware-type to 
> hardware-type, ambient temperature, size of the frequency step, etc.
>
> On 2017-07-14 15:10, Eugene Grayver via USRP-users wrote:
>
>     I am running some experiments to understand the timing of TwinRX
>     tuning.  A very simple experiment shows that the tag indicating a
>     frequency change is not placed at the right sample.  Here’s a
>     capture: The dashed line indicates the tag sample number. 
>     However, there’s clearly something happening before the tag.  Note
>     that I am not using timed commands for this – just a regular tune
>     request.
>
>     _______________________
>     Eugene Grayver, Ph.D.
>     Aerospace Corp., Sr. Eng. Spec.
>     Tel: 310.336.1274
>     ________________________
>
>     _______________________________________________
>     USRP-users mailing list
>     USRP-users at lists.ettus.com <mailto:USRP-users at lists.ettus.com>
>     http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>

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