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:*[email protected] [mailto:[email protected]]
*Sent:* Friday, July 14, 2017 12:34 PM
*To:* Eugene Grayver <[email protected]>
*Cc:* [email protected]
*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
________________________
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