Building an Embedded Program

The default in a Cargo project is to compile for the host (native compilation). The stm32-code/standalone-app project has been configured for cross compilation to the ARM Cortex-M33 processor. This configuration can be seen in the Cargo configuration file (.cargo/config):

# .cargo/config
[build]
target = "thumbv8m.main-none-eabi" # = ARM Cortex-M33

The target thumbv8m.main-none-eabi can be broken down as:

• thumbv8m.main - we generate instructions for the Armv8-M Mainline architecture running in Thumb-2 mode (actually the only supported mode on this architecture)
• none - there is no Operating System
• eabi - use the ARM Embedded Application Binary Interface, with Soft Float support
  • f32 and f64 are passed to functions in normal CPU registers (like R0), instead of in FPU registers (like S0)

✅ Inside the folder stm32-code, use the following command to cross compile the program:

cargo build --bin standalone-hello

Building the application also requires a Rust Standard Library that has been pre-compiled for the thumbv8m.main-none-eabi target. Normally, you would have to add this component to cargo by using rustup target add thumbv8m.main-none-eabi, but we provide a rust-toolchain.toml that is used to determine which toolchains and targets should be installed automatically when in this folder.

The output of the compilation process will be an ELF (Executable and Linkable Format) file. The file will be placed in the target/thumbv8m.main-none-eabi directory.

✅ Run file target/thumbv8m.main-none-eabi/debug/standalone-hello and compare if your output is as expected.

Expected output:

$ file target/thumbv8m.main-none-eabi/debug/standalone-hello
target/thumbv8m.main-none-eabi/debug/standalone-hello: ELF 32-bit LSB executable, ARM, EABI5 version 1 (GNU/Linux), statically linked, with debug_info, not stripped