🦾Mechatronic Systems Integration Unit 4 – Microcontrollers: Architecture and Programming

Microcontroller Basics

• Microcontrollers are single-chip computers designed for embedded applications
• Integrate a processor core, memory (RAM and ROM), and programmable input/output peripherals on a single integrated circuit
• Offer low cost, low power consumption, and high reliability compared to multi-chip systems
• Commonly used in automotive electronics, industrial control systems, medical devices, and consumer electronics
• Examples of popular microcontroller families include Arduino, PIC, and ARM Cortex-M series
• Microcontrollers execute programs stored in their non-volatile memory (ROM or Flash)
• Operate at clock frequencies ranging from a few MHz to hundreds of MHz depending on the application requirements

Architecture and Components

• Microcontroller architecture typically follows the Harvard architecture, which separates program memory and data memory
• Key components include the processor core (CPU), memory (RAM and ROM), clock generator, and input/output (I/O) ports
• CPU executes instructions, performs arithmetic and logic operations, and manages data flow
  • Common CPU architectures in microcontrollers: 8-bit (PIC), 16-bit (MSP430), and 32-bit (ARM Cortex-M)
• Memory stores program instructions (ROM) and temporary data (RAM)
  • ROM retains data even when power is off (non-volatile) and is used for firmware storage
  • RAM is volatile and used for temporary data storage during program execution
• Clock generator provides timing signals to synchronize operations within the microcontroller
• I/O ports enable communication with external devices (sensors, actuators, and peripherals)
• Additional components may include analog-to-digital converters (ADCs), digital-to-analog converters (DACs), and communication interfaces (UART, SPI, I2C)

Memory Types and Organization

• Microcontrollers use different types of memory for program storage and data storage
• Read-Only Memory (ROM) stores the firmware (program instructions) and is non-volatile
  • Types of ROM: Mask ROM, PROM, EPROM, and Flash memory
  • Flash memory is the most common type of ROM in modern microcontrollers due to its reprogrammability
• Random Access Memory (RAM) is volatile and used for temporary data storage during program execution
  • Static RAM (SRAM) retains data as long as power is supplied and is faster but more expensive than DRAM
  • Dynamic RAM (DRAM) requires periodic refresh to maintain data and is cheaper but slower than SRAM
• Memory organization in microcontrollers follows the Harvard architecture
  • Separate memory spaces for program memory (ROM) and data memory (RAM)
  • Allows simultaneous access to instructions and data, improving performance
• Memory addressing modes: direct, indirect, and indexed addressing
• Memory-mapped I/O: peripheral registers are accessed as memory locations, simplifying programming

Input/Output Interfaces

• Microcontrollers communicate with external devices through various input/output interfaces
• General-purpose input/output (GPIO) pins can be configured as digital inputs or outputs
  • Used for reading digital sensors (buttons, switches) or controlling digital actuators (LEDs, relays)
  • GPIO pins can often be configured as interrupt sources to detect external events
• Analog-to-digital converters (ADCs) convert analog signals from sensors to digital values
  • Used for reading analog sensors (temperature, pressure, light intensity)
  • ADC resolution (8-bit, 10-bit, 12-bit) determines the precision of the digital representation
• Digital-to-analog converters (DACs) convert digital values to analog signals
  • Used for generating analog control signals or waveforms
• Pulse-width modulation (PWM) outputs generate variable-duty-cycle square waves
  • Used for controlling motors, dimming LEDs, or generating analog signals
• Communication interfaces enable data exchange between the microcontroller and other devices
  • Universal Asynchronous Receiver/Transmitter (UART) for serial communication
  • Serial Peripheral Interface (SPI) for high-speed synchronous serial communication
  • Inter-Integrated Circuit (I2C) for multi-master, multi-slave communication
• Specialized interfaces: CAN bus (automotive), Ethernet, USB, and Bluetooth

Programming Languages and Tools

• Microcontrollers are programmed using various languages and tools depending on the architecture and application
• Low-level programming languages:
  • Assembly language provides direct control over the microcontroller's instructions and registers
  • Offers the highest performance and smallest code size but is more complex and less portable than high-level languages
• High-level programming languages:
  • C is the most common high-level language for microcontroller programming
  • Provides a balance between low-level control and high-level abstractions
  • C++ is used for object-oriented programming and can be used with microcontrollers that have sufficient memory and processing power
• Integrated Development Environments (IDEs) provide a user-friendly interface for writing, compiling, and debugging code
  • Examples: Arduino IDE, MPLAB X IDE (PIC), Keil MDK (ARM), and IAR Embedded Workbench
• Compilers convert high-level language code into machine code that can be executed by the microcontroller
  • Examples: GCC (GNU Compiler Collection), Clang, and proprietary compilers provided by microcontroller manufacturers
• Debugging tools help identify and fix errors in the code
  • In-circuit debuggers (ICD) and in-circuit emulators (ICE) allow stepping through code and monitoring variables
  • JTAG (Joint Test Action Group) is a common interface for debugging and programming microcontrollers

Instruction Set and Assembly Programming

• Microcontrollers execute machine code instructions that are specific to their architecture
• Instruction set architecture (ISA) defines the available instructions, registers, and memory addressing modes
• Common instruction categories:
  • Data transfer instructions: move data between registers and memory (MOV, LD, ST)
  • Arithmetic instructions: perform mathematical operations (ADD, SUB, MUL, DIV)
  • Logical instructions: perform bitwise operations (AND, OR, XOR, NOT)
  • Control flow instructions: modify the program counter to control execution flow (JMP, CALL, RET)
• Assembly language is a low-level programming language that uses mnemonics to represent machine code instructions
  • Each assembly language instruction corresponds to a specific machine code instruction
  • Provides direct control over the microcontroller's hardware but is less portable and harder to maintain than high-level languages
• Assembly language syntax includes opcodes (instruction mnemonics), operands (registers or memory addresses), and labels (symbolic names for memory locations)
• Assemblers convert assembly language code into machine code that can be executed by the microcontroller
• Inline assembly allows embedding assembly language code within high-level language (C or C++) programs for performance-critical sections

Interrupts and Timers

• Interrupts are signals that temporarily suspend the normal execution flow to handle high-priority events
• Interrupt sources can be external (GPIO pins, communication interfaces) or internal (timers, ADC, DAC)
• Interrupt service routines (ISRs) are special functions that are executed when an interrupt occurs
  • ISRs should be short and fast to minimize the time spent in the interrupt context
  • Interrupt priorities determine which interrupt is serviced first when multiple interrupts occur simultaneously
• Interrupt handling steps: save context, execute ISR, restore context, and resume normal execution
• Timers are hardware components that generate periodic interrupts or measure time intervals
  • Commonly used for generating PWM signals, implementing real-time clocks, or triggering periodic events
  • Timer modes: interval timer (generates interrupts at fixed intervals) and capture/compare (measures pulse width or generates PWM)
• Watchdog timers (WDT) are special timers that reset the microcontroller if it becomes unresponsive due to software or hardware faults
  • WDT must be periodically reset by the software to prevent a system reset
  • Helps improve system reliability and fault tolerance

Interfacing with Sensors and Actuators

• Microcontrollers interact with the physical world through sensors and actuators
• Sensors convert physical quantities (temperature, pressure, light intensity) into electrical signals
  • Analog sensors (thermistors, photoresistors, strain gauges) produce continuous voltage or current signals proportional to the measured quantity
  • Digital sensors (DHT11 temperature and humidity sensor, DS18B20 digital temperature sensor) provide digital outputs using communication protocols like I2C or 1-Wire
• Actuators convert electrical signals into physical actions (motion, light, sound)
  • Examples: DC motors, stepper motors, servos, relays, and LEDs
  • Motor control techniques: PWM for speed control, H-bridge for direction control, and PID for closed-loop control
• Signal conditioning circuits are often required to interface sensors and actuators with microcontrollers
  • Amplifiers (op-amps) increase the signal strength of low-level sensor outputs
  • Filters (passive or active) remove noise or unwanted frequencies from sensor signals
  • Level shifters (transistors or dedicated ICs) convert between different voltage levels (e.g., 5V sensors to 3.3V microcontrollers)
• Sensor fusion combines data from multiple sensors to improve accuracy or derive additional information
  • Example: combining accelerometer and gyroscope data for orientation estimation

Real-Time Operating Systems (RTOS)

• RTOS is a specialized operating system designed for real-time applications with strict timing constraints
• Provides a framework for managing tasks, scheduling, and inter-task communication
• Key features of an RTOS:
  • Task management: allows defining multiple tasks with different priorities and scheduling policies
  • Preemptive scheduling: higher-priority tasks can interrupt lower-priority tasks to ensure timely execution
  • Inter-task communication: provides mechanisms for tasks to exchange data and synchronize their activities (semaphores, message queues, mailboxes)
  • Resource management: handles allocation and deallocation of shared resources (memory, peripherals) to avoid conflicts
• Common RTOS for microcontrollers: FreeRTOS, Zephyr, Mbed OS, and RIOT
• Benefits of using an RTOS:
  • Simplifies the development of complex, multi-tasking applications
  • Improves system reliability and determinism by ensuring tasks meet their deadlines
  • Provides a modular and scalable architecture for managing software components
• Challenges of using an RTOS:
  • Increased memory footprint and processing overhead compared to bare-metal programming
  • Requires careful design and configuration to avoid priority inversion and deadlocks
  • Debugging can be more complex due to the interaction between tasks and the RTOS kernel

Debugging and Testing Techniques

• Debugging is the process of identifying and fixing errors (bugs) in the software or hardware
• Debugging techniques for microcontrollers:
  • Using an Integrated Development Environment (IDE) with built-in debugging features (breakpoints, step-through, variable watch)
  • Employing hardware debuggers (JTAG, SWD) to control the microcontroller's execution and inspect memory and registers
  • Adding debug print statements (e.g., using UART) to output variable values or execution flow information
  • Using logic analyzers or oscilloscopes to capture and visualize digital or analog signals
• Testing ensures that the microcontroller-based system meets its functional and performance requirements
• Types of testing:
  • Unit testing: testing individual components or modules in isolation
  • Integration testing: testing the interaction between different components or modules
  • System testing: testing the complete system under various operating conditions and scenarios
  • Acceptance testing: verifying that the system meets the end-user requirements and specifications
• Test-driven development (TDD) is a software development approach where tests are written before the actual implementation
  • Helps ensure code quality, maintainability, and reduces the likelihood of introducing bugs
• Continuous integration (CI) and continuous deployment (CD) practices can be applied to microcontroller projects
  • Automated build, test, and deployment processes to catch errors early and streamline development

Applications in Mechatronic Systems

• Mechatronic systems integrate mechanical, electrical, and software components to create intelligent and automated systems
• Microcontrollers play a central role in mechatronic systems by providing the computational power and I/O capabilities needed to control and monitor the system
• Examples of mechatronic systems using microcontrollers:
  • Industrial automation: PLCs (Programmable Logic Controllers) and embedded controllers for process control, motion control, and machine vision
  • Robotics: microcontrollers for robot control, sensor integration, and communication
  • Automotive systems: engine control units (ECUs), anti-lock braking systems (ABS), and electronic stability control (ESC)
  • Medical devices: pacemakers, insulin pumps, and prosthetic limbs
• Key considerations when using microcontrollers in mechatronic systems:
  • Real-time performance: ensuring that control loops and critical tasks execute within their specified deadlines
  • Reliability and fault tolerance: implementing error handling, watchdog timers, and redundancy to maintain system operation under adverse conditions
  • Power management: optimizing power consumption to extend battery life or reduce heat generation
  • Communication and networking: selecting appropriate communication interfaces (CAN, Ethernet, wireless) for data exchange between system components
• Model-based design and simulation tools (MATLAB/Simulink, LabVIEW) can accelerate the development of mechatronic systems by allowing rapid prototyping and virtual testing
• Hardware-in-the-loop (HIL) testing involves integrating the microcontroller with a simulated environment to validate its performance and functionality before deployment in the real system