chapter four

4 Startup and Initialization in Bare-Metal Rust

 

This chapter covers

  • Defining the memory layout for embedded Rust applications using custom linker scripts (including FLASH/RAM regions, section mapping, and stack/vector table placement).
  • Understanding and implementing the Cortex‑M boot/reset flow, from the microcontroller’s reset sequence to minimal startup logic (manual memory initialization, reset handler, and hand‑off to the main program).
  • Writing the smallest functional no_std Rust application for bare-metal targets.
  • Handling exceptions and interrupts safely: covering manual and runtime-crate approaches alongside idiomatic patterns for sharing data between contexts

In Chapter 3 we looked at the foundational project structure and build system knowledge essential for embedded Rust work. Building directly on these concepts, Chapter 4 dives into the heart of bare-metal programming, showing how Rust firmware starts from power-up, how the system initializes itself, and how core responsibilities like memory mapping, interrupt handling, and runtime setup are accomplished in a no_std world.

4.1 Defining the memory layout for your embedded Rust program

4.1.1 Memory initialization: LMA, VMA, and data movement

4.1.2 Defining physical memory regions

4.1.3 Mapping output sections

4.1.4 A Complete minimal linker script example

4.1.5 Inspecting the memory layout

4.2 Understanding the reset sequence & processor initialization

4.2.1 Overview of the MCU boot sequence

4.2.2 A detailed look at reset vector fetching and execution

4.2.3 Manually creating a vector table in Rust

4.2.4 A side note on the vector table’s configuration

4.3 Initializing Rust’s runtime in a bare-metal environment

4.3.1 Defining the reset handler

4.3.2 Writing a minimal startup routine in Rust

4.3.3 Optional additional initialization steps

4.3.4 Linker script reference for initialization symbols

4.4 Writing a minimal no_std Rust application

4.4.1 Disabling the standard library and the default entry point

4.4.2 Defining a custom entry point function

4.4.3 Implementing the panic handler