Question over the Silder in GRC

Hi all,

I am using USRP N210 and GRC. I have a question over changing a USRP
parameter using a slider in GRC.

If I want to change the TX frequency from 2GHz to 4GHz using a slider,
we know, during this process, the slider would experience many
values, such as 2.1, 3, 3.55, 3.888 and so on, how USRP would react to
these in-between values? Is there some mechanism to prevent the USRP
from overloaded if I move the slider very fast? Should the slider value
hold on for some time before sending the value to USRP?



On Wed, Oct 09, 2013 at 05:15:04PM -0400, Baokun Liu wrote:

hold on for some time before sending the value to USRP?
Hi Baokun,

haven’t checked this, but are you sure the event doesn’t get triggered
once you let go of the slider? At least that’s what I thought would


Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin B.
Research Associate

Kaiserstraße 12
Building 05.01
76131 Karlsruhe

Phone: +49 721 608-43790
Fax: +49 721 608-46071

KIT – University of the State of Baden-Württemberg and
National Laboratory of the Helmholtz Association

Thanks, Martin.

In fact, the event would be triggered as imagined. I want to know
each in-between value during moving the slider would be sent to USRP,
the USRP would react to each value? Does the value have to hold on for
time before the event is triggered?



It sounds like when you say “in between” you mean the period of time
when the user stop dragging the slider and the next time they stop
the slider.

In general, when people ask this question the area of focus is the
of time when they are dragging the slider.


Trying to figure that out, I went and had a look at the source code of
the wxgui slider.
In fact, it had a demo mode that could be accessed when just calling the
python file as main:
$python gr-wxgui/python/wxgui/
However, that was broken, so I fixed it; pull request against master has
been sent.

Using the repaired demo I was able to find out that intermediate values
are given at random intermediate points, so changing a slider from its
minimum to its maximum as fast as possible yields a (seemingly) random
selection of values in between.