USRP Codegen error : Nontunable property 'ChannelMapping' may only be assigned once.

Hi all,

I am trying to use code generation to accelerate my usrp fucntion. However, when I set ChannelMaping to '[1 2]' to receive data from both antennas on B210, the error 'Nontunable property 'ChannelMapping' may only be assigned once' popped up. How can I solve this?

[Matan Silver]

Hi Xianglong,

To best answer your question, it would be helpful to have some example code or reproduction steps. Could you show a minimal example of how you are using Support Package for USRP to get this error? For example, are you generating code from MATLAB, or are you generating code for a model using the USRP Simulink blocks?

In the mean time, there is some information I can give you based on the context of your question which may be helpful.

For the SDRuTransmitter and SDRuReceiver System Objects, ChannelMapping is a Nontunable property. Nontunable properties have restrictions on when they can be modified. See this doc page for more info on that:

https://www.mathworks.com/help/matlab/matlab_prog/define-property-attributes-1.html

Does that help narrow down if you are modifying ChannelMapping in a place that is disallowed?

Please let me know if you can reply with reproduction steps--I might be able to get you a more helpful answer.

Matan

[XIANGLONG WANG]

Hi Matan,

Thanks for your reply. My code is to receive signal from both channels and compare them in spectrum.

In my main function, I use codgen by:

if compileIt
    codegen('runSignalSpectrum', '-args', {coder.Constant(prmUSRP)}); 
end
if useCodegen
   clear runSignalSpectrum_mex 
   runSignalSpectrum_mex(prmUSRP);
else
   runSignalSpectrum(prmUSRP);
end

And in runSignalSpectrum:

function runSignalSpectrum(prmUSRP)

persistent rxRadio hSpectrum

if isempty(rxRadio)

    rxRadio = comm.SDRuReceiver(...
        'Platform',             'B210', ...
        'SerialNum',            prmUSRP.Address, ...
        'MasterClockRate',      prmUSRP.MasterClockRate, ...
        'CenterFrequency',      prmUSRP.USRPCenterFrequency, ...
        'Gain',                 prmUSRP.USRPGain, ...
        'DecimationFactor',     prmUSRP.USRPDecimationFactor, ...
        'SamplesPerFrame',      prmUSRP.USRPFrameLength, ...
        'ChannelMapping',       [1 2], ...
        'OutputDataType',       'double');

    hSpectrum = spectrumAnalyzer(...);
end

% Some Processing Code

release(hSpectrum);
release(rxRadio);
end

If I remove the 'Channel Maping' property, the code generation will success.

Answer 1

[Karunya Choppara]

Here the property 'ChannelMapping' of system object comm.SDRuReceiver is a non tunable property, and cannot be changed in between the simulation.

The error is seen as the ChannelMapping is assumed as 1, while setting the other parameters. The error happens as it tries to tune the ChannelMapping to [1 2] later.

Set the Channel Mapping to [1 2] after specifying the radio address, as below

rxRadio = comm.SDRuReceiver(...

'Platform', 'B210', ...

'SerialNum', prmUSRP.Address, ...

'ChannelMapping', [1 2], ...

'MasterClockRate', prmUSRP.MasterClockRate, ...

'CenterFrequency', prmUSRP.USRPCenterFrequency, ...

'Gain', prmUSRP.USRPGain, ...

'DecimationFactor', prmUSRP.USRPDecimationFactor, ...

'SamplesPerFrame', prmUSRP.USRPFrameLength, ...

'OutputDataType', 'double');

[XIANGLONG WANG]

Thanks Karunya! This works for me.