Re: [Discuss-gnuradio] Retune Request Time

Hello Richard,

The Python "API" is a minimal wrapper of the C++ API. You can call nearly every function of the multi_usrp class on a USRP sink or source object in Python. The function names are altered slightly because it makes no sense to call, for instance, set_rx_freq, on a USRP sink.

Here is the declaration of the set_center_freq function for the USRP source block.
https://github.com/gnuradio/gnuradio/blob/master/gr-uhd/lib/usrp_source_impl.h#L90

::uhd::tune_result_t set_center_freq(const ::uhd::tune_request_t tune_request, size_t chan);

This is converted to a call to set_rx_freq in the gr-uhd implementation.
https://github.com/gnuradio/gnuradio/blob/master/gr-uhd/lib/usrp_source_impl.cc#L142

Your program, and most others, are calling the function set_center_freq function with a frequency (number of herz) and no channel number. The frequency is automatically converted to a tune_request using the constructor which takes just a double. The default channel is 0 if one is not given.

http://files.ettus.com/manual/classuhd_1_1usrp_1_1multi__usrp.html#a9b61448f392466e20572fdcb042e8ec6

virtual tune_result_t uhd::usrp::multi_usrp::set_rx_freq(const tune_request_t & tune_request, size_t chan = 0)

To use your tune request with use it instead of a frequency in a call to set_center_freq

self.usrp = uhd.usrp_sink(device_addr=options.args, stream_args=uhd.stream_args('fc32'))

self.usrp.set_center_freq(900e6)
uhd.usrp_sink.get_center_freq()

tr = uhd.tune_request(901e6, 1e3)
self.usrp.set_center_freq(tr)

uhd.usrp_sink.get_center_freq()

Regards,

Derek

On Tue, Jun 14, 2016 at 12:13 PM, Richard Bell <address@hidden> wrote:

Martin,

If I create a USRP object

self.usrp = uhd.usrp_sink(device_addr=options.args, stream_args=uhd.stream_args('fc32'))

and initialize the USRP center frequency to 900e6

self.usrp.set_center_freq(900e6)

and then do

tr = uhd.tune_request(901e6, 1e3)

followed by

uhd.usrp_sink.get_center_freq()

it returns the original center freq of 900e6. My question is what is the tune_request doing?

Rich

On Mon, Jun 13, 2016 at 4:47 PM, Richard Bell <address@hidden> wrote:
I can call the C++ functions from Python? Why is there a separate python API, I'm confused.

Lets say I set an initial center frequency of 900 MHz to start the script off. You're saying that if the next frequency I want to hop to is within the ADC sampling rate, which in my case for the N210 is 100 MHz, I should manually tell the USRP to set the DSP_FREQ and leave the RF_FREQ alone for the fastest hop, and that the USRP automatic settings are not smart enough to figure this out?

If the above is true, it seems I should do something like this:
1) Ask the USRP what the current RF_FREQ is
2) Find the difference between RF_FREQ and the new center freq
3) If the difference is greater then 100 MHz, change the RF Freq, otherwise change the DSP freq

Is this correct?

On Mon, Jun 13, 2016 at 4:03 PM, Martin Braun <address@hidden> wrote:
Richard,

"use DSP tuning when possible" is not a valid policy.

In Python:

from gnuradio import uhd

rf_freq = 900e6
dsp_freq = 1e3
TR = uhd.tune_request(rf_freq, dsp_freq)
# Oh look it worked:
print TR.rf_freq_policy == uhd.tune_request.POLICY_MANUAL

So, in a nutshell, rf_freq and dsp_freq are used depending on the
respective policies, but there's no 'figure out smart tunes based on
state' policy.

-- M

On 06/13/2016 03:49 PM, Richard Bell wrote:
> Derek,
>
> that manual is the C++ API. How would I format the tune policy
> information in python? It's not clear to me looking at the C++ API and
> the Python API for the set_center_freq python function. Could you give
> an example of how you would call
>
> C++: http://files.ettus.com/manual/structuhd_1_1tune__request__t.html
> Python:
> http://www.gnuradio.org/doc/sphinx/uhd_blocks.html#gnuradio.uhd.usrp_sink
>
> set_center_freq(center_freq, <USE_DSP_TUNING_WHEN_POSSIBLE>)
>
> What goes in place of the careted argument?
>
> Rich
>
> On Mon, Jun 13, 2016 at 3:31 PM, Derek Kozel <address@hidden
> <mailto:address@hidden>> wrote:
>
> Hi Rich,
>
> You can create and pass a tune_request_t into the set frequency call
> of a USRP object. This gives you control of how it tunes. By default
> it does not optimize for speed to my knowledge.
> http://files.ettus.com/manual/structuhd_1_1tune__request__t.html
>
> Depending on what USRP you are using there are self calibration
> thresholds which will cause a retune to incur a delay when tuning
> outside of a certain range. On the B200 for instance this range is
> 100MHz.
>
> Regards,
> Derek
>
> On Mon, Jun 13, 2016 at 3:05 PM, Richard Bell
> <address@hidden <mailto:address@hidden>> wrote:
>
> I am using set_center_freq(center_freq) in my python script to
> retune my USRP to various center frequencies. Does this command
> use the smartest retune technique to get to the new frequency?
>
> For example, if I want to retune from 900.000 MHz to 900.001 MHz
> ( a 1 kHz change), will it use DSP tuning instead of RF tuning
> for speed? Is there a way to control this through python?
>
> In my testing, it seems the retune time is constant whether I
> make a 1 GHz hop, a 3 MHz hop or a 1 kHz hop, which makes me
> think I'm overlooking something.
>
> Thanks,
> Rich
>
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From:	Derek Kozel
Subject:	Re: [Discuss-gnuradio] Retune Request Time
Date:	Tue, 14 Jun 2016 13:37:40 -0700