function msfcn_varpulseizzy(block)
% Level-2 M-file S-function to implement a variable pulse width generator
%   Copyright 1990-2007 The MathWorks, Inc.

% This S-function takes a desired pulse width (in percentage
% of the period of a Pulse Generator block) and sets the PulseWidth
% property in a Pulse Generator block. The result is a variable-width
% pulse signal. The S-function assumes the model contains only one Pulse
% Generator block and modifies the PulseWidth of that block.

setup(block);

%endfunction

function setup(block)

% Register number of ports
 block.NumDialogPrms = 1;
block.NumInputPorts  = 1;
block.NumOutputPorts = 0;

% Setup port properties to be inherited or dynamic
block.SetPreCompInpPortInfoToDynamic;
block.SetPreCompOutPortInfoToDynamic;

% Override input port properties
block.InputPort(1).DatatypeID  = 0;  % double
block.InputPort(1).Complexity  = 'Real';

% Register sample times
block.SampleTimes = [0 0];

% Register methods
block.RegBlockMethod('PostPropagationSetup', @DoPostPropSetup);
block.RegBlockMethod('InitializeConditions', @InitializeConditions);
block.RegBlockMethod('Start', @Start);
block.RegBlockMethod('Outputs', @Outputs);
block.RegBlockMethod('Update', @Update);
block.RegBlockMethod('Terminate', @Terminate);

%endfunction

function DoPostPropSetup(block)

% Initialize the Dwork vector
block.NumDworks = 2;

% Dwork(1) stores the value of the next pulse width
block.Dwork(1).Name            = 'x1';
block.Dwork(1).Dimensions      = 1;
block.Dwork(1).DatatypeID      = 0;      % double
block.Dwork(1).Complexity      = 'Real'; % real
block.Dwork(1).UsedAsDiscState = true;

% Dwork(2) stores the handle of the Pulse Geneator block
block.Dwork(2).Name            = 'BlockHandle';
block.Dwork(2).Dimensions      = 1;
block.Dwork(2).DatatypeID      = 0;      % double
block.Dwork(2).Complexity      = 'Real'; % real
block.Dwork(2).UsedAsDiscState = false;

%endfunction

function Start(block)

% Populate the Dwork vector
block.Dwork(1).Data = 0;

% Obtain the Pulse Generator block handle
pulseGen = find_system(gcs,'BlockType','DiscretePulseGenerator');
blockH = get_param(pulseGen{1},'Handle');
block.Dwork(2).Data = blockH;

%endfunction

function InitializeConditions(block)

% Set the initial pulse width value
d=50;
set_param(block.Dwork(2).Data, 'PulseWidth', num2str(d));

%endfunction

function Outputs(block)
% Update the pulse width value
if block.InputPort(1).Data>50
    d=d-2;  %reduce dutycycle by 2
else
    d=d+2; %increment dutycycle by 2
end
set_param(block.Dwork(2).Data, 'PulseWidth', num2str(d));

%endfunction

function Update(block)
d=50;
% Store the input value in the Dwork(1)
block.Dwork(1).Data = d;

%endfunction

function Terminate(block)

%endfunction

50
d=d-2; %reduce dutycycle by 2
else
d=d+2; %increment dutycycle by 2
end
set_param(block.Dwork(2).Data, ‘PulseWidth’, num2str(d));

%endfunction

function Update(block)
d=50;
% Store the input value in the Dwork(1)
block.Dwork(1).Data = d;

%endfunction

function Terminate(block)

%endfunction
>

Thanks for the feedback. I actually decided to go with the second option since it made more sense for me to have an initialization step and subsequent output steps.

Have you played around with the dynamic port dimensions in the latest prerelease (2009b)? I’m looking at having a bus with elements of varying dimensions, but I haven’t found any documentation on the updates to the bus editor. I take it prereleases don’t come with documentation?

P.S. Glad y’all spotted the bug!

Thanks,
Jeff

• Use Embedded MATLAB - As long as you have an structure of arrays (not an array of structures) you should be able to pass the bus out of an Embedded MATLAB block.
• Mask the level 2 M-file s-function in a subsystem with a bus creator at the output. If there are 100 signals, you can pass them out separately and wire them into the bus. If the bus is more complicated, you may need to cascade the bus creators. This would have a high one time cost, but it will give you a nice interface to the system.

I think the Embedded MATLAB option may be best, though, the Embedded MATLAB language is a subset of what you can do in the M-file S-function. Embedded MATLAB blocks don’t have states the way S-functions do, so you may have to rething your code if you rely on them.

Regarding your second comment about the S-function builder bug, thanks for reporting it. Technical Support is looking into this.

Just FYI, I found a bug in the S-Function Builder. If you try to create an S-Function with a bus output and no inputs, the builder messes up while generating the code (inserts an extra comma where the input argument usually is) that causes build errors, rendering the builder GUI useless.

Thanks,
Jeff

I have a large struct that I need to pass through a simulink model (presumably by bus object). The struct is created in a Level 2 M-file S-Function. Unfortunately it doesn’t look like Level 2 M-file S-Functions support bus ports, do you have any recommendations for making this work? The struct is way too complicated to multiplex into a single matrix.

Thanks!

@Gaurav Thaiba - If you are simply looking for a block to output a pulse signal, there are some pulse generators in the Simulink Sources library. You could also model a PWM signal using SimElectronics or SimPowerSystems. Search the documentation for PWM.