What is Scatter File in ARM: Explanation and Usage

A scatter file in ARM is a text file used to control how a program's code and data are placed in memory during linking. It defines memory regions and assigns program sections to specific addresses, helping organize the layout of embedded system firmware.

How It Works

A scatter file acts like a map for the linker, telling it exactly where to put different parts of your program in the device's memory. Imagine you have a box with different compartments (memory regions), and you want to place your items (code, data) in specific compartments. The scatter file describes these compartments and assigns each item to one.

During the build process, the linker reads the scatter file to arrange the program sections such as code, read-only data, and variables into the defined memory areas. This is crucial in embedded systems where memory is limited and must be carefully managed to ensure the program runs correctly.

Example

This example shows a simple scatter file defining two memory regions and placing code and data sections accordingly.

scatter

LR_IROM1 0x08000000 0x00010000  {    ; Load region starting at address 0x08000000 with size 64KB
  ER_IROM1 0x08000000 0x00008000  {  ; Execution region for code, 32KB
    *.o (RESET, +First)               ; Reset vector and startup code
    *(InRoot$$Sections)               ; Root sections
    *(+RO)                          ; Read-only code and constants
  }
  RW_IRAM1 0x20000000 0x00002000  {  ; Execution region for RAM data, 8KB
    *(+RW +ZI)                      ; Read-write and zero-initialized data
  }
}

When to Use

Use a scatter file when you need precise control over memory layout in ARM embedded projects. It is essential for placing code in flash memory and variables in RAM, especially when working with microcontrollers that have multiple memory types.

For example, you might want to place interrupt vectors at a fixed address or reserve memory for special hardware functions. Scatter files help you organize your program to meet these hardware requirements and optimize memory usage.

Key Points

• A scatter file defines memory regions and assigns program sections to them.
• It guides the linker in placing code and data in specific memory addresses.
• Essential for embedded systems with limited and specialized memory.
• Helps meet hardware constraints like fixed interrupt vector locations.

Key Takeaways

A scatter file controls how program sections are placed in ARM memory during linking.

It defines memory regions and assigns code and data to specific addresses.

Scatter files are crucial for managing limited memory in embedded systems.

They help meet hardware requirements like fixed addresses for special functions.