Custom Code Integration (Legacy Code Tool) - Model-Based Development

Legacy Code Tool (LCT)

What Is the Legacy Code Tool?

The Legacy Code Tool (LCT) creates an S-Function wrapper that allows existing C functions (legacy MCAL drivers, hand-written algorithms, third-party libraries) to be called from a Simulink model as a block. The model calls the C function during simulation and the generated code calls it directly.

LCT generates: an S-Function block (.c + .tlc), a block mask, and documentation. The C function signature is described in a MATLAB structure.

LCT Example: Wrapping an MCAL ADC Function

MATLABlct_adc_wrapper.m

% Legacy Code Tool: wrap Adc_ReadGroup() for use in Simulink

def = legacy_code("initialize");

% Specify the legacy C function signature
def.SFunctionName   = "Adc_ReadGroup_SFcn";
def.OutputFcnSpec   = "void Adc_ReadGroup(uint8 p1, uint16 y1[4])";
% p1: input parameter (ADC group ID)
% y1: output array (4 ADC results)

def.HeaderFiles     = {"Adc.h"};
def.SourceFiles     = {"Adc_Stub.c"};  % stub for simulation
def.IncPaths        = {"$(PROJECT_ROOT)/include/mcal"};

% Generate S-Function source
legacy_code("sfcn_cmex_generate",  def);
% Compile for simulation
legacy_code("compile",             def);
% Generate TLC for code generation (no wrapper -- calls C directly)
legacy_code("sfcn_tlc_generate",   def);
% Generate Simulink block
legacy_code("slblock_generate",    def);

% Result: a Simulink block "Adc_ReadGroup_SFcn" that:
% - During simulation: calls Adc_Stub.c (returns test values)
% - In generated code: calls Adc_ReadGroup() directly
% - Passes type checking and MAAB compliance
% - Appears in Code Gen Report with correct traceability

Inline TLC for Direct Function Calls

MATLABlct_direct_call.m

% For maximum code generation efficiency:
% Use "InlineOption = Inline" to generate direct function call
% (no wrapper function in generated code)

def.Options.singleCPPMexFile = false;
def.Options.isInlineAccordingToMisraC = true;

% Generated code with Inline option:
% Adc_ReadGroup(ADC_GROUP_SENSORS, &SpeedController_B.AdcResults[0]);

% Without Inline (wrapper generated):
% Adc_ReadGroup_SFcn_Outputs_wrapper(&SpeedController_B.AdcGroup,
%                                    SpeedController_B.AdcResults);
% --> wrapper calls --> Adc_ReadGroup(...);
% Wrapper adds overhead and obscures traceability to MCAL

Summary

The Legacy Code Tool is the correct way to integrate existing C code into an MBD model. The alternatives are worse: writing a manual S-Function (time-consuming, error-prone), using a MATLAB Function block to call C functions (loses type information), or wrapping the call in a post-processing script that patches generated code (breaks traceability and requires re-patching every time the model changes). LCT-generated blocks participate fully in Model Advisor checks, code generation reports, and back-to-back MiL/SiL testing. The stub file pattern (Adc_Stub.c for simulation, real Adc.c for the ECU) is the standard approach that enables MiL testing without hardware while generating code that calls the real MCAL driver.

🔬 Deep Dive — Core Concepts Expanded

This section builds on the foundational concepts covered above with additional technical depth, edge cases, and configuration nuances that separate competent engineers from experts. When working on production ECU projects, the details covered here are the ones most commonly responsible for integration delays and late-phase defects.

Key principles to reinforce:

Configuration over coding: In AUTOSAR and automotive middleware environments, correctness is largely determined by ARXML configuration, not application code. A correctly implemented algorithm can produce wrong results due to a single misconfigured parameter.
Traceability as a first-class concern: Every configuration decision should be traceable to a requirement, safety goal, or architecture decision. Undocumented configuration choices are a common source of regression defects when ECUs are updated.
Cross-module dependencies: In tightly integrated automotive software stacks, changing one module's configuration often requires corresponding updates in dependent modules. Always perform a dependency impact analysis before submitting configuration changes.

🏭 How This Topic Appears in Production Projects

Project integration phase: The concepts covered in this lesson are most commonly encountered during ECU integration testing — when multiple software components from different teams are combined for the first time. Issues that were invisible in unit tests frequently surface at this stage.
Supplier/OEM interface: This is a topic that frequently appears in technical discussions between Tier-1 ECU suppliers and OEM system integrators. Engineers who can speak fluently about these details earn credibility and are often brought into critical design review meetings.
Automotive tool ecosystem: Vector CANoe/CANalyzer, dSPACE tools, and ETAS INCA are the standard tools used to validate and measure the correct behaviour of the systems described in this lesson. Familiarity with these tools alongside the conceptual knowledge dramatically accelerates debugging in real projects.

⚠️ Common Mistakes and How to Avoid Them

Assuming default configuration is correct: Automotive software tools ship with default configurations that are designed to compile and link, not to meet project-specific requirements. Every configuration parameter needs to be consciously set. 'It compiled' is not the same as 'it is correctly configured'.
Skipping documentation of configuration rationale: In a 3-year ECU project with team turnover, undocumented configuration choices become tribal knowledge that disappears when engineers leave. Document why a parameter is set to a specific value, not just what it is set to.
Testing only the happy path: Automotive ECUs must behave correctly under fault conditions, voltage variations, and communication errors. Always test the error handling paths as rigorously as the nominal operation. Many production escapes originate in untested error branches.
Version mismatches between teams: In a multi-team project, the BSW team, SWC team, and system integration team may use different versions of the same ARXML file. Version management of all ARXML files in a shared repository is mandatory, not optional.

📊 Industry Note

Engineers who master both the theoretical concepts and the practical toolchain skills covered in this course are among the most sought-after professionals in the automotive software industry. The combination of AUTOSAR standards knowledge, safety engineering understanding, and hands-on configuration experience commands premium salaries at OEMs and Tier-1 suppliers globally.