Module 02

Welcome to this module on processing units in embedded systems. In this module, we will explore the central processing units (CPUs) commonly used in embedded systems, their characteristics, and the factors to consider when selecting a CPU for an embedded application. We will also discuss real-time processing and power efficiency, which are critical aspects of embedded system design.

1. Overview of Embedded Systems

1.1 Embedded System

A dedicated computing system designed to perform specific tasks or functions within a larger system.

1.2 Characteristics

• Typically performs a narrow range of functions.

• Often operates in real-time or with strict timing constraints.

• Resource-constrained (limited memory and processing power).

• Reliable and robust.

1.3 Embedded vs. General-Purpose Computing

• Embedded Systems: Optimized for specific tasks or applications.

• General-Purpose Computers: Designed for a wide range of applications.

2. Central Processing Units (CPUs) in Embedded Systems

2.1 Types of Embedded CPUs

• Microcontrollers: Integrated CPU, memory, and peripherals on a single chip.

• Microprocessors: CPU with external memory and peripheral interfaces.

• Digital Signal Processors (DSPs): Specialized for signal processing tasks.

2.2 Key CPU Characteristics

• Clock Speed: Determines the number of instructions executed per second.

• Instruction Set Architecture (ISA): Defines CPU's instruction set and capabilities.

• Word Size: Size of data processed in a single instruction (e.g., 8-bit, 16-bit, 32-bit).

• Pipeline Depth: Number of stages in the instruction pipeline.

• Cache Size: Level 1 (L1) and Level 2 (L2) cache for faster access to memory.

2.3 CPU Architectures

• RISC (Reduced Instruction Set Computer): Simple, fixed-length instructions.

• CISC (Complex Instruction Set Computer): Complex, variable-length instructions.

• ARM: Widely used architecture in embedded systems due to its power efficiency.

3. Selecting the Right CPU for Your Embedded System

3.1 Performance Requirements

• Matching CPU performance to application needs.

• Balancing speed and power consumption.

3.2 Power Consumption

• Critical in battery-powered and energy-efficient systems.

• Consider idle power, dynamic power, and leakage power.

3.3 Cost Considerations

• Cost per unit and development costs.

• Evaluating performance-to-cost ratio.

3.4 Peripherals and Interfaces

• Compatibility with required peripherals (USB, UART, I2C, etc.).

• Availability of GPIO pins and analog interfaces.

4. Real-Time Processing in Embedded Systems

4.1 What is Real-Time Processing?

• Processing that must respond within specified time constraints.

• Critical for applications like automotive, robotics, and medical devices.

4.2 Hard vs. Soft Real-Time Systems

• Hard Real-Time: Must meet deadlines without exception.

• Soft Real-Time: Missed deadlines are tolerable but undesirable.

4.3 Real-Time Operating Systems (RTOS)

• Software layer for managing tasks and priorities.

• Examples: FreeRTOS, VxWorks, QNX.

5. Power Efficiency in Embedded CPUs

5.1 Low Power Design Strategies

• Minimizing clock speed when not needed.

• Using low-power modes and sleep states.

• Efficiently managing peripherals.

5.2 Power Management Techniques

• Dynamic Voltage and Frequency Scaling (DVFS).

• Clock gating to disable unused modules.

• Power gating to completely shut off parts of the CPU.

5.3 Sleep Modes and Wake-up Mechanisms

• CPUs can enter sleep modes to conserve power.

• External events or timers can trigger wake-up.

6. Case Studies

• Explore examples of CPUs used in real-world embedded applications.

• Discuss how CPU selection impacted system performance and power efficiency.

7. Conclusion

7.1 Recap of Key Points

• Embedded systems have specific characteristics and require careful CPU selection.

• CPUs vary in performance, power efficiency, and cost.

• Real-time processing and power efficiency are crucial in embedded design.

7.2 Future Trends in Embedded Processing

• Advancements in CPU architectures.

• Integration of AI and machine learning.

• Increased focus on security in embedded systems.

8. Conclusion

This lecture provides a comprehensive overview of processing units in embedded systems, including CPU types, characteristics, selection criteria, real-time processing, power efficiency, and case studies. Understanding these concepts is vital for designing efficient and reliable embedded systems in various application domains.