STM32 barebones setup

Barebones STM32 CLI based project for the nucle-F303RE board.

Chip Specifications

MCU	STM32F303RET6
CPU Core	ARM®32-bit Cortex®-M4 CPU
Speed	72 Mhz with 8 Mhz oscillator
LED pin	D13 or PA_5

Item	Size	Map
RAM	64 KB	0x2000 0000 - 0x2001 0000
Flash	512 KB	0x0800 0000 - 0x0808 0000

Getting started

Do a git clone (git clone ssh://gitea@gitea.hak8or.com:6022/hak8or/Minimal_Embedded.git) to get a copy of all the code in this repository.

Getting everything setup might present some difficulty depending on how familiar you are with gdb, openocd, and debugging in general for embedded applications. On the high level, you have openocd talking to the STM32 chip over SWD using the on board ST-Link V2. You can actually telnet into the openocd server on port 4444 and do basic functions like flashing the chip, reseting, halting, etc. To compile run make, flash run make flash, and start run make start. To do all those in one go, simple run make full.

CMSIS

ARM has made efforts to standerdize various parts of code needed for developing for ARM based microcontrollers. CMSIS contains code needed to interact with the core, such as NVIC_Enable_IRQ(), while vendors such as STM create a large header file (stm32f30x.h) that contains all the register interacting code.

Cross Compiler

Most distro's have an ARM cross compiler in their repository (Arch has one), but for whatever reason you may want to get an ARM maintained version of GCC here manually, which is what I am using. First we need to make sure our cross compiler is accessible by either your path variable or symlinking it to /usr/bin. You don't need to do this if running -arm-none-eabi-gcc --version works from where you are running the makefile.

Flashing

To program the chip, we just run make flash.

GDB

And now for GDB, which may be problematic depending on which distro you are using since GDB seems to require the 32 bit ncurses library. For example, I am using Arch which requires the following changes:

yaourt -S ncurses        # Install ncurses
vim /etc/pacman.conf     # Enable multilib by uncommenting both [multilib]
                         # and the include path.
yaourt -Syu              # Get the multilib mirror.
youart -S lib32-ncurses  # Install the 32 bit library.

Start up openocd using openocd -f interface/stlink-v2-1.cfg -f target/stm32f3x.cfg and to start up gdb do arm-none-eabi-gdb --tui --eval-command="target remote localhost:3333" firmware.elf. This loads the elf file including all it's metadata into gdb and talks to openocd over port 3333. Here is a list of commands you can run in GDB, through make sure to use help often because GDB offers a ton of functionality.

Commands	Description
s	Single step source C/C++.
mon reg	Dumps the registers.
mon reg pc	Dumps a specific register, like PC.
display foo	Dumps the contents of variable foo.
print foo	Dumps the contents of variable foo.
info frame	Dumps the current stack frame.
x 0x20000000	Dumps the contents of memory at location.
layout split	Display the C/C++ source and assembly view.
layout regs	Display the registers and source.
stepi	Single step assembly.
break 5	Set a breakpoint on C/C++ source line 5.
continue	Run forever or till we hit a breakpoint.

Resources

• Exception Vector
• Barebones example
• Awesome explanation on SO of barebones example
• Even awesomer explanation of barebones example
• Another barebones example
• Walkthrough of low level embedded ARM ecosystem
• Nucle-F303RE
• MCU Datasheet