"Bare Metal" STM32 Programming

This repository contains the source files for programming an STM32 F070RB without the use of the STM32 Cube toolchain. This project nominally follows along with Vivonomicon's tutorial. (See further reading section.)

The current program (main.c) repeatedly increments a value which may be inspected by GDB. It also flashes GPIO PA5 which is associated with the user LED on the NUCLEO board for the STM32 F070RB using the SysTick timer (built in to the Cortex-M CPU). A complete vector table (with most entries pointing to a default interrupt handler) is loaded as well and should be inspectable with GDB or nm.

A Renode machine description is provided in sim/renode that can be used to simulate the code and peripherals. A GDB server is automatically started on port 4141 when simulating.

Directories

A map of the directories present in the repository is shown below.

stm32-bare-metal/           # Root
├── conf/                   # Configuration files (Meson cross compile conf.)
├── docs/                   # Additional notes and information
├── sim/                    # Simulations
│   └── renode/             # Renode models and configuration
├── src/                    # Application related source code
└── sys/                    # Target system source code and hardware abstraction

Build & Debug

The current version of the software is built using meson and may be compiled to debug.elf in the build directory of your choosing with the following commands.

meson setup <build-dir> --cross-file conf/<cross-file>
cd <build-dir>
meson compile

The chip can be debugged by running the following commands in separate bash terminals. I have chosen to use the open source ST Link utility recommended by Vivonomicon. (See link in further reading section.)

st-util
arm-none-eabi-gdb <build-dir>/debug.elf

(As a reminder to myself, st-util may be sent to the background with Ctrl-Z and bg. This permits the use of one terminal, though mixes up outputs from GDB pgrep st-util may be used to get its pid to kill it when finished.)

Simulation

A rudimentary Renode simulation is provided in sim/renode. To simulate the software, follow the build instructions and then use the script sim/renode/stm32f070rb_init.resc in the Renode shell. The command to load the script in the Renode shell follows.

include @sim/renode/stm32f070rb_init.resc

(Assuming that the Renode shell was started in the project's root directory.)

Branches

At the time of writing, there is a branch of the repository exp/nob that demonstrates the "nob" build system as an alternative to Meson. The objective of nob is to provide a build system for C projects that requires only the C compiler as a dependency. This branch was provided by @sirlilpanda (website).

Next Steps

Other than following the Vivonomicon tutorial, I'd also like to explore:

• Simulating the code execution in a framework such as Renode.
• Building some peripheral drivers from scratch.
• Unifying the hardware description for peripheral drivers and simulation by using device trees.
• DIY multithreading.
• Unit testing.
• Switch away from meson to a more embedded friendly build chain. See exp/nob for nob-based alternative. (More information in the branches section.)

Further Documentation

• VSCodium Configuration

Further Resources

• Vivonomicon "Bare Metal" STM32 article series.
• Open source ST Link utilities
• STM32 F070RB Product Page.
• Meson Build System.
• Renode.