Building an Embedded Program

The default in a Cargo project is to compile for the host (native compilation). The nrf52-code/radio-app project has been configured for cross compilation to the ARM Cortex-M4 architecture. This configuration can be seen in the Cargo configuration file (.cargo/config):

# .cargo/config
[build]
target = "thumbv7em-none-eabihf" # = ARM Cortex-M4

The target thumbv7em-none-eabihf can be broken down as:

  • thumbv7em - we generate instructions for the Armv7E-M architecture running in Thumb-2 mode (actually the only supported mode on this architecture)
  • none - there is no Operating System
  • eabihf - use the ARM Embedded Application Binary Interface, with Hard Float support
    • f32 and f64 can be passed to functions in FPU registers (like S0), instead of in integer registers (like R0)

✅ Inside the folder nrf52-code/radio-app, use the following command to cross compile the program to the ARM Cortex-M4 architecture.

cargo build --bin hello

The output of the compilation process will be an ELF (Executable and Linkable Format) file. The file will be placed in the target/thumbv7em-none-eabihf directory.

✅ Run $ file target/thumbv7em-none-eabihf/debug/hello and compare if your output is as expected.

Expected output:

$ file target/thumbv7em-none-eabihf/debug/hello
hello: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), statically linked, with debug_info, not stripped