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Verify FIR Filter on ARM Cortex-M Processor in MATLAB

This example shows how to use the Code Replacement Library (CRL) for ARM Cortex-M processor with DSP System object™. The example uses a dsp.FIRFilter System object to filter two sine waves of different frequencies.

Prerequisites

Before you start with this example, install these MathWorks® products:

  • DSP System Toolbox Support Package for ARM Cortex-M Processors

  • DSP System Toolbox

  • Embedded Coder

Task 1: Setup and Simulate

1. Open the ex_fircmsis_tut_ml example function, which implements a lowpass FIR filter object.

2. Create two sine wave signals with 1KHz and 3KHz frequency, respectively.

sin1 = dsp.SineWave('Amplitude',1,'Frequency',1000,...
                     'SampleRate',8000, 'SamplesPerFrame', 75,...
                     'OutputDataType', 'single');
sin2 = dsp.SineWave('Amplitude',4,'Frequency',3000,...
                     'SampleRate',8000, 'SamplesPerFrame', 75,...
                     'OutputDataType', 'single');

3. Create a spectrum analyzer to view the spectrum of the input and filtered output.

scope = dsp.SpectrumAnalyzer('SampleRate',8e3,'ShowLegend',true,...
                          'PlotAsTwoSidedSpectrum', false, ...
                          'RBWSource', 'Property',...
                          'RBW',8000/260, 'Window','Kaiser', ...
                          'OverlapPercent', 80,...
                          'YLimits', [-76 56], 'SpectralAverages',10);

4. Simulate the example

NN = 2000;
for k = 1:NN
   x1k = sin1(); % generate 1K Hz sine wave
   x3k = sin2(); % generate 3K Hz sine wave
   n1 = randn(size(x1k), 'single')*sqrt(.05); % generate noise signal
   u1 = x1k+x3k+n1;
   y1 = ex_fircmsis_tut_ml(u1);
   scope([u1,y1]);
end

Task 2: Configure for Code Replacement

1. Create a code generation configuration object for use with codegen when generating a C/C++ static library.

cfgEx = coder.config('lib');
cfgEx.CodeReplacementLibrary = 'ARM Cortex-M';
cfgEx.HardwareImplementation.ProdHWDeviceType = 'ARM Compatible->ARM Cortex';
cfgEx.GenCodeOnly = true;

2. Open the Custom code panel of the configuration dialog and verify the settings.

cfgEx.dialog

Task 3: Generate code

1. Change your current folder in MATLAB to a temporary writable folder. Copy the MATLAB file to the temporary folder. tempdirObj = dstarmexample.dstTempdir('ex_fircmsis_tut_ml_workflow'); dstarmsrc = which('ex_fircmsis_tut_ml'); dstarmtmpdir = tempdirObj.tempDir; type(fullfile(dstarmsrc)) copyfile(dstarmsrc, dstarmtmpdir, 'f');

function y1 = ex_fircmsis_tut_ml(u1)

#codegen

  persistent firfilter;
  if isempty(firfilter)
      firfilter = dsp.FIRFilter('Numerator', fir1(63, 0.33));
  end
  y1 = firfilter(u1);
end

2. Generate C code for the MATLAB function ex_fircmsis_tut_ml.m.

codegen ex_fircmsis_tut_ml -args single(u1) -config cfgEx -report

3. When code generation finishes successfully, click View report to display the code generation report.

4. Click on the ex_fircmsis_tut_ml.c file. Notice the CMSIS functions, arm_fir_init_f32 and arm_fir_f32 in the ex_fircmsis_tut_ml function.

Task 4: Verify the generated C code on target

The generated code can be compiled and executed on ARM Cortex-M target by using a user- selected tool chain, for example, ARM® KEIL™ uVision® IDE.

Task 5: Fixed-Point FIR Filter

Following similar steps of Task 3, you can generate fixed-point C code for the MATLAB function ex_fircmsis_tut_ml_q15.m.

dstarmsrc = which('ex_fircmsis_tut_ml_q15');
copyfile(dstarmsrc, dstarmtmpdir, 'f');
codegen ex_fircmsis_tut_ml_q15 -args fi(u1, true, 16, 15) -config cfgEx -report

Run the following code to delete the temporary directory. status = tempdirObj.cleanUp;

dstarmexample.displayDSPARMEndOfDemoMessage(mfilename)