Documentation

Create a local working folder, for example, c:\ex_2ndOrder_filter.

Change to the docroot\toolbox\fixpoint\examples folder. At the MATLAB command line, enter:

cd(fullfile(docroot, 'toolbox', 'fixpoint', 'examples')) 

Copy the ex_2ndOrder_filter.m and ex_2ndOrder_filter_test.m files to your local working folder.

 The ex_2ndOrder_filter Function

function y = ex_2ndOrder_filter(x) %#codegen
  persistent z
  if isempty(z)
      z = zeros(2,1);
  end
  % [b,a] = butter(2, 0.25)
  b = [0.0976310729378175,  0.195262145875635,  0.0976310729378175];
  a = [1, -0.942809041582063,  0.3333333333333333];

 
  y = zeros(size(x));
  for i = 1:length(x)
      y(i) = b(1)*x(i) + z(1);
      z(1) = b(2)*x(i) + z(2) - a(2) * y(i);
      z(2) = b(3)*x(i)        - a(3) * y(i);
  end
end

 The ex_2ndOrder_filter_test Script

% ex_2ndOrder_filter_test
%
% Define representative inputs
N = 256;                   % Number of points
t = linspace(0,1,N);       % Time vector from 0 to 1 second
f1 = N/2;                  % Target frequency of chirp set to Nyquist
x_chirp = sin(pi*f1*t.^2); % Linear chirp from 0 to Fs/2 Hz in 1 second
x_step = ones(1,N);        % Step
x_impulse = zeros(1,N);    % Impulse
x_impulse(1) = 1;

% Run the function under test
x = [x_chirp;x_step;x_impulse];
y = zeros(size(x));
for i = 1:size(x,1)
  y(i,:) = ex_2ndOrder_filter(x(i,:));
end

% Plot the results
titles = {'Chirp','Step','Impulse'}
clf
for i = 1:size(x,1)
  subplot(size(x,1),1,i)
  plot(t,x(i,:),t,y(i,:))
  title(titles{i})
  legend('Input','Output')
end
xlabel('Time (s)')
figure(gcf)

disp('Test complete.')

Navigate to the work folder that contains the file for this example.

On the MATLAB Toolstrip Apps tab, under Code Generation, click the app icon.

Set Numeric Conversion to Convert to single precision.

Click Next to go to the Define Input Types step.

The app screens ex_2ndOrder_filter.m for code violations and code generation readiness issues. The app does not find issues in ex_2ndOrder_filter.m.

On the Define Input Types page, to add ex_2ndOrder_filter_test as a test file, browse to ex_2ndOrder_filter_test. Click Open.

Click Autodefine Input Types.

The test file runs and displays the outputs of the filter for each of the input signals. The app determines that the input type of x is double(1x256).

Click Next to go to the Check for Run-Time Issues step.

On the Check for Run-Time Issues page, the app populates the test file field with ex_2ndOrder_filter_test, the test file that you used to define the input types.

Click Check for Issues.

The app generates a single-precision MEX function from ex_2ndOrder_filter. It runs the test file ex_2ndOrder_filter_test replacing calls to ex_2ndOrder_filter with calls to the generated MEX function. If the app finds issues, it provides warning and error messages. Click a message to highlight the problematic code in a window where you can edit the code. In this example, the app does not detect issues.

Click Next to go to the Generate Code page.

In the Generate dialog box, set Build type to Static Library.

Set Language to C.

For other settings, use the default values.

To generate the code, click Generate.

MATLAB Coder builds the project and generates a C static library and supporting files in the default subfolder, codegen/lib/ex_2ndOrder_filter.