Lecture Notes: Microcontroller Memory

Introduction

• Importance of understanding microcontroller memory due to limited space.
• Writing code carefully to avoid memory overflow.
• Focus on types of memory and code examples.

Types of Microcontroller Memory

Flash Memory

• Non-volatile memory.
• Used to store program code.
• Contents remain even when powered off.

RAM (Random Access Memory)

• Volatile memory.
• Used for program variables and data.
• Contents lost when powered off.

EEPROM

• Optional smaller type of non-volatile memory.
• Used mainly for storing configuration data (not covered in detail).

Memory Size Example

• Example microcontroller: 16 KB Flash, 512 Bytes RAM.
• Flash memory is usually larger than RAM in most microcontrollers.

Code Compilation Process

1. Source Code
   • Written in C (example).
2. Compilation
   • Compiler translates source code to machine code.
3. Linking
   • Linker organizes machine code into sections based on layout specified in a link script.
4. Execution
   • Flash programmer writes machine code to flash memory.
   • RAM is initialized during the startup code.

Compiler and Linker Roles

• Compiler
  • Divides code into sections (text, BSS, data).
• Linker
  • Uses link script to determine where sections go in memory.

Code Example: Memory Allocation

• Using standard blink example to demonstrate memory allocation for variables.
• Variables:
  • Global Variable: initialized, ends in data section (counts against RAM and Flash).
  • Constant Variable: identical values, ends in const section (only counts against Flash).
  • Uninitialized Global Variable: defaults to zero, ends in BSS (counts against RAM).
  • Local Variable: allocated on the stack during function execution.
  • Static Variable: behaves like global, initialized during startup code.

Memory Inspection

• Use IDE Memory Browser to inspect RAM and Flash.
• Map file shows where each variable is stored in memory.

Final Remarks on Memory Management

• Optimize code to save Flash space (avoid floating-point operations, use simpler implementations).
• Use tools to analyze memory usage:
  • elf size: check section sizes in executable.
  • readelf: inspect symbols and their sizes.

Recommendations

• Choose microcontrollers with more memory than necessary to avoid optimization issues.
• Balancing memory usage with performance needs is essential in embedded programming.