(Clean Architecture by Robert C. Martin)
This chapter explores how the principles of Clean Architecture apply to embedded systems. Embedded systems, which are constrained by hardware resources and tightly coupled to hardware functionality, require a unique approach to achieve flexibility, maintainability, and testability. Robert C. Martin explains how to decouple hardware dependencies and maintain clean, modular software design in embedded environments.
Key Concepts of Clean Embedded Architecture
1. Challenges in Embedded Systems
- Hardware Constraints:
- Limited CPU, memory, and storage.
- Tight Coupling:
- Embedded systems often directly interact with hardware components like sensors, actuators, or microcontrollers.
- Real-Time Requirements:
- Timing constraints are critical, as systems must respond to events within strict deadlines.
- Difficult Testing:
- Testing is often hardware-dependent, making it hard to isolate software logic.
2. Applying Clean Architecture to Embedded Systems
The principles of Clean Architecture can be adapted to address these challenges by:
a. Decoupling Hardware from Software
- Isolate hardware-specific code behind interfaces.
- The core logic should not directly interact with hardware components.
Example: Abstracting Sensor Data
// Hardware Interface
typedef struct {
int (*readTemperature)();
} TemperatureSensor;
// Implementation for Specific Hardware
int hardwareReadTemperature() {
// Hardware-specific code to read temperature
return analogRead(TEMP_PIN);
}
TemperatureSensor sensor = { .readTemperature = hardwareReadTemperature };
b. Separating Policies from Details
- Policies (business logic) should reside in the core layers, independent of hardware details.
- Hardware interactions belong to the outermost layer, following the Dependency Rule.
c. Using Dependency Injection
- Inject hardware dependencies into the core logic at runtime.
- This ensures that the core logic is independent of specific hardware implementations.
3. Layered Architecture in Embedded Systems
Core Logic (Entities Layer):
- Contains algorithms and business rules.
- Independent of hardware and real-time constraints.
Use Cases (Application Layer):
- Coordinates between the core logic and hardware interfaces.
- Implements workflows like “Monitor Temperature” or “Control Motor Speed.”
Hardware Abstractions (Interface Adapters):
- Adapters convert hardware signals into formats usable by the application layer.
- Example: Translating raw sensor data into temperature readings.
Hardware Drivers (Frameworks and Drivers Layer):
- Interact directly with hardware components.
- Example: GPIO control, ADC (Analog-to-Digital Converter), or I2C communication.
4. Example: Temperature Control System
Entities Layer (Core Logic):
- Contains the logic for determining whether to turn a fan on or off.
int shouldTurnOnFan(int currentTemp, int threshold) {
return currentTemp > threshold;
}
Use Cases Layer:
Implements the workflow of monitoring temperature and controlling the fan.
void monitorTemperature(TemperatureSensor* sensor, FanController* fan, int threshold) {
int temp = sensor->readTemperature();
if (shouldTurnOnFan(temp, threshold)) {
fan->turnOn();
} else {
fan->turnOff();
}
}
Interface Adapters:
- Adapters for the hardware-specific implementation of sensors and fan controllers.
typedef struct {
void (*turnOn)();
void (*turnOff)();
} FanController;
void hardwareTurnOnFan() {
digitalWrite(FAN_PIN, HIGH);
}
void hardwareTurnOffFan() {
digitalWrite(FAN_PIN, LOW);
}
FanController fan = { .turnOn = hardwareTurnOnFan, .turnOff = hardwareTurnOffFan };
Hardware Drivers:
- The actual hardware interaction code (e.g., GPIO control).
int hardwareReadTemperature() {
// Example: Read temperature from a sensor
return analogRead(TEMP_PIN);
}
Main Component:
- Initializes hardware and orchestrates the system.
int main() {
TemperatureSensor sensor = { .readTemperature = hardwareReadTemperature };
FanController fan = { .turnOn = hardwareTurnOnFan, .turnOff = hardwareTurnOffFan };
while (1) {
monitorTemperature(&sensor, &fan, 25);
}
}
5. Testing Embedded Systems
- Testing embedded systems is challenging due to hardware dependencies, but Clean Architecture makes it easier:
- Unit Testing: Test core logic (entities) in isolation without requiring hardware.
void testShouldTurnOnFan() {
assert(shouldTurnOnFan(30, 25) == 1);
assert(shouldTurnOnFan(20, 25) == 0);
}
void testMonitorTemperature() {
TemperatureSensor mockSensor = { .readTemperature = mockReadTemperature };
FanController mockFan = { .turnOn = mockTurnOnFan, .turnOff = mockTurnOffFan };
monitorTemperature(&mockSensor, &mockFan, 25);
// Verify fan state changes
}
Key Takeaways
- Decouple Hardware and Logic:
- Use interfaces to abstract hardware interactions.
- Follow the Dependency Rule:
- Core logic depends on abstractions, not on hardware details.
- Design for Testability:
- Isolate business rules to make them testable without hardware.
- Balance Constraints:
- While embedded systems are resource-constrained, Clean Architecture principles can still be adapted to fit.