Simulink code generation: simple state machine and its code

This paper studies simple state machine modeling and its generated code .

1 Simulink Medium Chart modular

Chart The module is used to describe the jump relationship between states , It is often used in the process of automotive software development . You need to define the state in the state machine 、 Jump condition between States 、 I / O, local variables, etc . This article will use a simple example to study state machine modeling , And understand the principle through the generated code .

2 State machine modeling

If there is a need now , When the vehicle speed is higher than a certain value , The output variable is the motion state , Below this value, it is at rest . The first reaction to this problem is to use if-else Conditional judgment implementation , But it can also be implemented by state machine modeling . The state machine modeling process will be demonstrated later .

1） First pull out one Chart modular , At this time, there are no input / output interfaces on both sides of it ;

2） Double click in Chart, Open it up Model Explorer, Add input interface as VehicleSpeed, The output interface is MotionState, Respectively, the input signals are vehicle speed information , The output signal is the vehicle motion state ;

here ,Chart The module will be refreshed to have an I / O port ;

3） next , Need to be in Chart Internally defined state 、 State jump condition ;

The explanation is as follows ：

• The two rectangular boxes represent Stop and Move Two states , In the upper left corner is the name of the state ;
• In the status box en and du Indicates when entering a state or in a state , Executed statements , Here is the time to enter the state MotionState Assign the corresponding constant ;
• The arrows between states indicate a jump , The statements in square brackets are bar conditions , Here is when the vehicle speed is greater than a certain value Stop Jump to Move, Less than this value from Move Jump meeting Stop;
• Stop The arrow above indicates that the default jump to at the initial time Stop in ;

4） In the last step STOP/MOVE/P_VehStopThres These three variables have not been defined , The state machine doesn't know what it is , So first Matlab Workspace definition ;

Define... In the workspace MOVE and STOP by boolen type , The values are 1 and 0;P_VehStopThres Defined as single type , Values for 0.5, It means that the vehicle speed exceeds 0.5 It is judged to be in motion , On the contrary, it is in a static state ;

next , stay Chart The three variables defined in the module are Parameter Parameters , Inherit Simulink The type of ;

5） Last , Set up Chart The working language in is C Language , The default is Matlab Language ; Check Execute (enter) Chart At Initialization Indicates that the state machine is initialized at zero time ; These two are bloggers' working habits , It can be configured according to your own needs ;

thus ,Chart The modeling of the module is completed

3 Model simulation

stay Chart Add a... Outside the module Signal Builder Input module , One Scope output module .

Signal Builder The vehicle speed is defined in the input module , from 0 To 0.9 Back to 0, The expected result should be a static state first , Re movement state , And then rest .

Run the model , The results are in line with expectations ;

4 Code generation

Replace the input and output of the model with port mouth ,Ctrl + B The generated code .

1） First , In addition to the global variables corresponding to the input and output ports , Another global variable is generated demo_DW, It stores the current status .

This state can take two enumerators ：demo_IN_Move and demo_IN_Stop.

2） stay Step Function , Generated a lot of conditional judgment nesting . The basic idea is the same as that in the state machine , Will judge demo_DW, The current state , And state jump conditions CAN_VehicleSpeed, Thus different... Are given in the branch MotionState Value of output .

This code is pretty good to understand , You can have a look and study for yourself .

In this case , Use one... Directly Switch The module judges the vehicle speed , The output status is more convenient , The code will also be simpler . But if the execution statement in the state is more complex , Or the jump between States is more complicated , Or should we use Stateflow State machine for modeling . This not only ensures the readability of the model , Policy modeling in the form of state machine will also greatly reduce the possibility of logic errors .

5 summary

This paper studies the modeling and code generation of state machine . Note the configuration , And global variables representing states in the generated code .

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