1. Basic S-Functions and TLC Coding

2. Basic S-Functions and TLC
Creating Custom Blocks for Simulink
Simulink has the notion of S-functions to create user defined blocks
S-functions can be written in M, C, or FORTRAN
We will focus on C
Embedded Coder cannot code generate an S-Function without the help of a TLC (Target Language Compiler)
All MotoHawk Blocks are created using S-Functions, Masks, and TLC using interfaces defined by Mathworks
No sneaky “special” functions or APIs are used
MotoHawk maintains a very thin interface to Simulink to simplify issues that can be caused during Matlab version changes

3. Help Material
S-Functions are Described in the Simulink Help

4. Add a S-Function from the Simulink Browser
S-Function Primer
Add a S-Function from the Simulink Browser
Set the Name and add any parameters
Recommend using company_sfun_xxx

5. S-Function Primer (con’t)
Copy <MatlabInstall>\simulink\src\sfuntmpl_basic.c to your local project directory
Rename to the same name you chose in the s-function block, in this case mototron_sfun_timesX.c
Edit c file: > edit mototron_sfun_timesX.c
This must be changed to match filename

6. Editing the S-Function C File
Set the number of Parameters in the function ssSetNumSFcnParams(S, 1);
One Parameter
One Parameter

7. Input Port Definition
Set Input Port Attributes

8. Input Port Direct FeedThrough
What does Input Port Direct Feed Through mean?
This tells the block sorter that this input port is used as part of the calculation of the output ports
Setting it to Zero means that the ports are independent and the sorter does not need to make sure that blocks upstream are calculated first…This is NOT usually the case.
Setting it to One means that this input must be calculated prior to the execution of the block. This is USUALLY the case.

9. Output Port Definition
Set Output Port Attributes

10. Set Options
Set Code Generation Options

11. How Do I Know What Options to Set?
<MATLABDIR>\simulink\include\simstruc.h has the documentation

12. Setting the Sample Time
Set to Inherited Sample Time

13. Creating the Simulation Behavior
mdlOutputs contains code for simulation
Example to multiply Input by Parameter Value

14. Note resultant file (may be mex32 on newer versions)
Build DLL
Use Matlab’s mex command to compile file
Choose LCC if asked
Note resultant file (may be mex32 on newer versions)

15. Check Simulation Behavior
Run in simulation to verify operation

16. Port Data Types
We didn’t specify data types for the ports so they defaulted to double.
To accommodate different datatypes requires deeper s-function knowledge

17. S-Function Wrapup
S-function describes the block with respect to the Simulation Engine (and the Diagram Checker)
S-Function describes port data types, sizes, number of parameters, sample times, and memory allocations
S-Functions contain code that runs in the simulation but that code is not generated into a MotoHawk build, TLC will help us with that
S-Function Syntax and Help are contained in Matlab’s Help and simstruc.h

18. See Matlab Help regarding Mask Details
Masks
Interacting with the User is defined by a Mask
Select S-function block, right click->Mask Subsystem
See Matlab Help regarding Mask Details

19. Parameters are design time choices needed from the Application Builder
Add a Parameter
Parameters are design time choices needed from the Application Builder
Tunable means adjustable at run time (not available in MotoHawk)
Evaluate as a MatLab expression

20. Document on Mask Icon
Show the designer’s choice on the block icon for documentation

21. Add some Help Text
Add Mask Help, Copyright Recommended

22. Masks present the custom block to the user
Mask Wrapup
Masks present the custom block to the user
Masks can pre-compute via scripts in the Initialization pane
Heavy lifting of sorting, querying the model for information, rationalizing the designers choices, etc should be done here.
Masks should show as much of the Parameter choices as possible on the icon.
Don’t make readers look for data in dialogue boxes
Help text should not be overlooked.
Too much help documentation is almost enough
Good block design should also make the functions and parameters obvious
Masks don’t do any code generation but can pre-compute information used by the code generator

23. TLC Telling the Code Generator What to Do
TLC (Target Language Compiler) is the language that drives the Real Time Workshop code generator
TLC can be thought of a as a Macro Expansion Language
TLC has many computer language constructs like variables, loops, and functions
TLC directives use the % sign to indicate that this is a TLC statement
Anything without a % sign is either dumped to the current source file or ignored if no file is being created
The code generator makes essentially 4 passes over the model to collect code generation directives

24. TLC Documentation
TLC is descibed in Matlab’s Help under Real Time Workshop

25. Must match the s-function name and TLC file name
TLC File Contents
TLC Files Must have an Implements directive and certain “Callback” functions
Must match the s-function name and TLC file name
Run once if at least one instance of the block is in the model.
Typically we add header files here.
Note “VOID” means no active output file during this pass
Run once for each instance of the block in the model. Note no output active. Usually we add blocks to lists here

26. TLC File Contents
TLC Files Must have an Implements directive and certain “Callback” functions
Generate code destined for Startup function
Generate code destined for triggered susbsystems.

27. TLC File Contents
Anything without a % directive is dumped to the output

28. Asking The Code Generator for Names
LibBlockInputSignal() and LibBlockOutputSignal ask the code generator for signal names, Parameter[] gets parameter value
%<var> expands the TLC variable var into the output
Note Constant value is expanded as the literal value.
Output is actually a global variable.

29. First, we built the S-function DLL from a c file (language #1)
Custom Blocks So Far
First, we built the S-function DLL from a c file (language #1)
Next, we masked the S-Function block to make it look good (language #2)
Finally, we wrote a TLC file (language #3) to generated embedded C (language #4).
Looking at the generated code, we see some issues
A global variable was created when obviously the expression could have been inlined costing no RAM
The S-Function C file is terribly complex (and we used the simple template)
We can address these two issues by using a better template

30. A better Approach
The MotoHawk Template s-function file contains all of the “Correct” settings for good code generation
Simply fill out details at the top, add the simulation behavior and most everything else is taken care of (see motohawk_mex_template.c for the details)

31. Reuse Outputs and Use Expressions
Fix S-Function Options to Re-use outputs (save memory) and Use Expressions if possible
Original required two global variables and a run time operation
Original required two global variables and a run time operation
Better version uses stack variable and no run time operation.

32. Custom Blocks are Powerful
Custom Block Wrapup
Custom Blocks are Powerful
Often times complex Simulink subsystems can be aggregated into a simple block
Lower Block count = faster update and compile times
Building them requires mastery of 4 languages
TLC drives the code generator
TLC documentation is readily available in Simulink
Look at both MotoHawk and Simulink TLC files for lots of examples
Warning, using MotoHawk provided TLC functions may break in the future. We don’t publish that as a public API so we reserve the right to change without notice.