PrinterFirmware_SIL_Linux

A full Software-in-the-Loop (SIL) test framework for STM32 firmware on Linux

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Overview

This project demonstrates how to compile an entire STM32 firmware application into a Linux shared object (.so) and test it in a Software-in-the-Loop (SIL) environment using Python, pytest, and lightweight plant models.

It mirrors how real QA teams validate embedded firmware (e.g., in printers, energy systems, or robotics) before flashing hardware.

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Project Architecture

libprinter_firmware.so (all STM32 firmware compiled for Linux)
+ HAL stubs (GPIO, ADC, Delay)
          │
          ▼
Simulated Plant Models (motor load, heater ambient, etc.)
          │
          ▼
Python Test Harness (pytest, numpy, matplotlib)

Each test drives the firmware through exported C APIs (via ctypes), feeds in simulated inputs, executes multiple scheduler “steps,” and verifies that system behavior (RPM, temperature, etc.) matches expectations.

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Folder Structure

PrinterFirmware_SIL_Linux/
├── Core/
│   ├── Inc/
│   │   ├── firmware.h          # Public firmware API (exposed to Python)
│   │   ├── system_state.h      # Global state machine and fault tracking
│   │   ├── paperfeed.h         # Paper feed motor controller interface
│   │   └── heater_control.h    # Heater control interface
│   └── Src/
│       ├── main.c              # Entry point for host-mode execution
│       ├── firmware_api.c      # Glue layer exposing firmware.h functions
│       ├── system_state.c      # Basic READY/INIT state transitions
│       ├── paperfeed.c         # Motor control logic (rpm, load response)
│       └── heater_control.c    # Heater control (ambient & setpoint)
│
├── SIL_Stubs/
│   ├── hal_stubs.c             # Replaces HAL GPIO/Delay functions
│   ├── mock_adc.c              # Stub for ADC reads
│   └── timebase_stub.c         # Provides a fake system tick (HAL_GetTick)
│
├── tests/
│   ├── conftest.py             # Pytest fixture loading libprinter_firmware.so
│   ├── plant_model.py          # Simple Python models for motor & heater
│   ├── test_paperfeed.py       # Verifies motor control under load conditions
│   └── test_heater.py          # Verifies heater setpoint & ambient response
│
├── reports/                    # Test results and plots (created at runtime)
├── docs/
│   └── architecture.png        # Visual diagram of Python↔Firmware↔Plant flow
│
├── Makefile                    # Builds the firmware .so for host testing
├── requirements.txt            # Python dependencies
└── README.md                   # (this file)

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Toolchain and Dependencies

Build Tools

Tool	Purpose
gcc	Compiles firmware C code for host (Linux x86_64).
make	Automates build (creates build/libprinter_firmware.so).
ctypes (Python stdlib)	Loads and calls functions from .so.

Python Packages (from requirements.txt)

Package	Purpose
pytest	Core test framework for SIL regression.
pytest-html	Generates HTML test reports for QA.

Install all packages:

python3 -m venv venv
source venv/bin/activate
pip install -r requirements.txt

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Building the Firmware for Host (SIL Mode)

Run:

make

This compiles all .c files (firmware + stubs) into:

build/libprinter_firmware.so

This .so contains the entire firmware image (minus hardware drivers), now callable from Python via ctypes.

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Running SIL Tests

Run:

pytest -v --html=report.html --self-contained-html

Test Categories

Test	Description
test_paperfeed.py	Runs the paper feed motor controller through start/stop and load variations. Checks RPM response and decay.
test_heater.py	Verifies the heater reaches and tracks setpoint temperature under different ambients.
plant_model.py	Provides simple physical models for environment behavior.

Outputs:

• report.html — summary of test results
• (optional) plots or logs saved to reports/

Screenshot:

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How It Works (Execution Flow)

1. Python test loads the .so:

   fw = CDLL("./build/libprinter_firmware.so")

2. Calls exposed firmware APIs:

   fw.firmware_init()
   fw.firmware_cmd_paperfeed_start(1500.0)
   fw.firmware_step()
   rpm = fw.firmware_get_motor_rpm()

3. The .so executes the same C logic as your STM32 firmware, but using stubbed HAL functions (no hardware).
4. Python’s plant_model simulates environment feedback (e.g., motor load or ambient temp).
5. Assertions in pytest check firmware response against expectations.
6. The pipeline produces detailed HTML reports for QA traceability.

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Extending the Framework

Goal	How
Add more peripherals	Create additional stubs in SIL_Stubs/
Add more test scenarios	Create new test_*.py files under tests/
Integrate into CI	Add make && pytest stages to Jenkins/GitHub Actions
Include coverage/linting	Add pytest-cov, flake8 to dev-requirements.txt
Model complex physics	Expand plant_model.py (e.g., inertia, PID, noise)

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Continuous Integration Example

Typical Jenkins pipeline snippet:

stage('SIL Build & Test') {
    sh '''
        make
        pytest -v --junitxml=results.xml --html=report.html --self-contained-html
    '''
    archiveArtifacts artifacts: 'report.html, results.xml', fingerprint: true
}

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Credits

Created as a reference implementation for Firmware QA Engineers automating SIL verification of STM32 embedded systems using open-source tools.
Tested on Ubuntu 22.04 LTS with GCC 11 and Python 3.12.