Why 2 Linker script in STM32CubeIDE

Why Two Linker Scripts?

Understanding FLASH.ld and RAM.ld in STM32CubeIDE

When working with STM32CubeIDE to build embedded applications, you may notice that two linker scripts are generated by default:

• STM32F446RETX_FLASH.ld
• STM32F446RETX_RAM.ld

However, during the build process, only one linker script is used. This raises a common question: Why are two linker scripts generated, and what purpose do they serve? Let’s explore the reasons behind this and how you can switch between them depending on your development needs.

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Why Two Linker Scripts Are Generated

STM32CubeIDE generates two linker scripts to give you the flexibility to configure your program to run either from Flash or RAM. Both have distinct use cases:

1. Flash-based Execution (STM32F446RETX_FLASH.ld)

• Purpose: This is the default script for most embedded projects. It configures the program to run from Flash memory, which is non-volatile.
• Why Use Flash?: Flash retains data even after power cycles. It’s perfect for production code that needs to persist across reboots.

2. RAM-based Execution (STM32F446RETX_RAM.ld)

• Purpose: This script is used for running the entire application from RAM. RAM is volatile but offers faster access times.
• Why Use RAM?: Ideal for debugging and testing, since it avoids the need to frequently erase and write to Flash memory. This significantly speeds up development.

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How the Linker Scripts Work

Flash Linker Script (STM32F446RETX_FLASH.ld)

This script places:

• Program code (.text) → Flash
• Initialized data (.data) → RAM
• Uninitialized data (.bss) → RAM

MEMORY
{
  FLASH (rx)  : ORIGIN = 0x08000000, LENGTH = 512K
  RAM   (xrw) : ORIGIN = 0x20000000, LENGTH = 128K
}

Note: The .data section is special — it’s executed from RAM (VMA) but stored in Flash (LMA). You can learn more about VMA vs LMA in this blog post.

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RAM Linker Script (STM32F446RETX_RAM.ld)

This script places everything — code, initialized data, and uninitialized data — in RAM. Flash is ignored.

MEMORY
{
  RAM (xrw) : ORIGIN = 0x20000000, LENGTH = 128K
}

Used primarily for:

• Debug builds
• Temporary testing
• Fast code iteration

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When to Use Each Linker Script

Linker Script	When to Use	Pros	Cons
FLASH.ld (default)	Production builds	Non-volatile, persistent	Slower than RAM for code access
RAM.ld	Debugging, testing, prototyping	Fast execution, easy to modify	Volatile, not suitable for final deployment

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Does STM32CubeIDE Use Both Linker Scripts?

No. Only one script is active per build.

• Default: STM32F446RETX_FLASH.ld
• Optional: You can switch manually to STM32F446RETX_RAM.ld for RAM-based execution

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Switching to the RAM Linker Script in STM32CubeIDE

Here’s how to switch:

1. Right-click your project → Properties
2. Navigate to C/C++ Build > Settings
3. Under MCU GCC Linker > General, change the Linker Script file from STM32F446RETX_FLASH.ld → STM32F446RETX_RAM.ld
4. Click Apply, then Rebuild Project

Your application will now use the RAM-based layout for execution.

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Conclusion

STM32CubeIDE provides two linker scripts — one for Flash and one for RAM — to help developers manage memory layout depending on the context:

• Use Flash linker script for production-ready builds that must persist across power cycles.
• Use RAM linker script when debugging or testing code that needs to be modified and re-run frequently.

Understanding and switching between these linker scripts can speed up your development process and help you optimize your embedded application workflow.