请问使用 Simulink 中的 S-Function 如何实现以下代码的功能 (VCO) ？(How can I implement the following code (VCO) using S-Function in Simulink?)

以上用 Matlab 语言写的大概的逻辑；请问如何用 S-Function 实现该功能（Voltage Controlled Osillator）；关键点是变步长；不知道什么原因，我用 S-Function 写的代码总是报错；我写的 S-Function 代码，如下：

// The above approximate logic written in Matlab language; please ask how to implement the function (Voltage Controlled Osillator) with S-Function; the key point is to change the step size; I don't know what the reason is, the code I write with S-Function always reports an error; the S-Function code I wrote, is as follows:

function [sys,x0,str,ts,simStateCompliance] = voltageControlledOsillator(t,x,u,flag,v1,v2,f1,f2)

switch flag,

  % Initialization
  case 0,
    [sys,x0,str,ts,simStateCompliance]=mdlInitializeSizes;

  % Derivatives
  case 1,
    sys=mdlDerivatives(t,x,u);

  % Update
  case 2,
    sys=mdlUpdate(t,x,u);

  % Outputs
  case 3,
    sys=mdlOutputs(t,x,u);

  % GetTimeOfNextVarHit
  case 4,
    sys=mdlGetTimeOfNextVarHit(t,x,u,v1,v2,f1,f2);

  % Terminate
  case 9,
    sys=mdlTerminate(t,x,u);

  % Unexpected flags
  otherwise
    DAStudio.error('Simulink:blocks:unhandledFlag', num2str(flag));

end

%=============================================================================
function [sys,x0,str,ts,simStateCompliance]=mdlInitializeSizes

sizes = simsizes;

sizes.NumContStates  = 0;
sizes.NumDiscStates  = 0;
sizes.NumOutputs     = 1;
sizes.NumInputs      = 1;
sizes.DirFeedthrough = 0;
sizes.NumSampleTimes = 1;

sys = simsizes(sizes);

x0  = [];

str = [];

ts  = [-2 0];  % -2 means vriable step for simulating (Mr. Luo)

simStateCompliance = 'UnknownSimState';

%=============================================================================
function sys=mdlDerivatives(t,x,u)

sys = [];

%=============================================================================
function sys=mdlUpdate(t,x,u)

sys = [];

%=============================================================================
function sys=mdlOutputs(t,x,u)

sys = ~sys;

%=============================================================================
function sys=mdlGetTimeOfNextVarHit(t,x,u,v1,v2,f1,f2)

fs = (u-v1)*(f1-f2)/(v1-v2) + f1;
sampleTime = 1/fs/2;
sys = t + sampleTime;

%=============================================================================
function sys=mdlTerminate(t,x,u)

sys = [];

Answer 1

[Luo Gang]

我已经解决了这个问题；

问题有两点：

1，“sizes.DirFeedthrough = 0;”应该修改为“sizes.DirFeedthrough = 1;”

2，“sys = ~sys;”用法不正确；因此我用了一个中间离散状态变量。

更正后的代码如下：

function [sys,x0,str,ts,simStateCompliance] = voltageControlledOsillator(t,x,u,flag,v1,v2,f1,f2)

switch flag,

  % Initialization
  case 0,
    [sys,x0,str,ts,simStateCompliance]=mdlInitializeSizes;

  % Derivatives
  case 1,
    sys=mdlDerivatives(t,x,u);

  % Update
  case 2,
    sys=mdlUpdate(t,x,u);

  % Outputs
  case 3,
    sys=mdlOutputs(t,x,u);

  % GetTimeOfNextVarHit
  case 4,
    sys=mdlGetTimeOfNextVarHit(t,x,u,v1,v2,f1,f2);

  % Terminate
  case 9,
    sys=mdlTerminate(t,x,u);

  % Unexpected flags
  otherwise
    DAStudio.error('Simulink:blocks:unhandledFlag', num2str(flag));

end

%=============================================================================
% mdlInitializeSizes
% Return the sizes, initial conditions, and sample times for the S-function.
%=============================================================================
function [sys,x0,str,ts,simStateCompliance]=mdlInitializeSizes

sizes = simsizes;

sizes.NumContStates  = 0;
sizes.NumDiscStates  = 1;
sizes.NumOutputs     = 1;
sizes.NumInputs      = 1;
sizes.DirFeedthrough = 1;
sizes.NumSampleTimes = 1;   % at least one sample time is needed

sys = simsizes(sizes);

x0  = 0;

str = [];

ts  = [-2 0];  % -2 means vriable step for simulating (Mr. Luo)

simStateCompliance = 'UnknownSimState';

%=============================================================================
% mdlDerivatives
% Return the derivatives for the continuous states.
%=============================================================================
function sys=mdlDerivatives(t,x,u)

sys = [];

%=============================================================================
% mdlUpdate
% Handle discrete state updates, sample time hits, and major time step
% requirements.
%=============================================================================
function sys=mdlUpdate(t,x,u)

sys = 1-x;

%=============================================================================
% mdlOutputs
% Return the block outputs.
%=============================================================================
function sys=mdlOutputs(t,x,u)

sys = x;

%=============================================================================
% mdlGetTimeOfNextVarHit
% Return the time of the next hit for this block.  Note that the result is
% absolute time.  Note that this function is only used when you specify a
% variable discrete-time sample time [-2 0] in the sample time array in
% mdlInitializeSizes.
%=============================================================================
function sys=mdlGetTimeOfNextVarHit(t,x,u,v1,v2,f1,f2)

fs = (u-v1)*(f1-f2)/(v1-v2) + f1;
sampleTime = 1/fs/2;
sys = t + sampleTime;

%=============================================================================
% mdlTerminate
% Perform any end of simulation tasks.
%=============================================================================
function sys=mdlTerminate(t,x,u)

sys = [];