Brain

Microcontroller

The microcontroller reference is STM32F103C8T6, that means:

STM32
ARM-based 32-bit ST microcontroller
F
General purpose
103
Performance line
C
Pin count, 48 pins
8
Medium-density, 64 Kbytes of Flash memory
T
Package type, LQFP
6
Temperature range, -40 to 85 ºC

Dependencies

In order to work with this project we need to install some dependencies first:

  • The GCC ARM compiler and debugger.
  • A C standard library implementation.
  • OpenOCD for programing and debugging.

In Fedora we can easily install those dependencies with:

dnf install arm-none-eabi-gcc arm-none-eabi-gdb arm-none-eabi-newlib openocd

Workspace

We will be using the libopencm3 [3] firmware library. Our workspace is based on the simple template from that project.

  1. Clone the project including submodules to get libopencm3:

    git clone --recursive git@github.com:Theseus/bulebule.git

  2. Setup libopencm3:

    cd bulebule/
./scripts/setup_libopencm3.sh

  3. Compile Bulebule

    cd src/
make

Note

The makefile on the src folder combines the libopencm3.target.mk file, the board STM32F1 makefile and the Bulebule project relative paths.

Programmer

The programmer is a generic ST-Link V2. Connecting this programmer to the board is very simple, just make sure to connect these pins together:

Board Programmer
3V3 3.3V
SWIO SWDIO
SWCLK SWCLK
GND GND

Note

The programmer uses an USB interface, which means we might need to set the proper permissions for our user:

sudo usermod -a -G dialout USER_NAME

We may need to log out and back in for this change to take effect.

Alternatively we could add some UDEV rules in /etc/udev/rules.d/99-stlink.rules:

ATTRS{idVendor}=="0483", ATTRS{idProduct}=="3748", MODE="0666"

And then simply reload the rules without logging out:

udevadm control --reload-rules

To program the microcontroller we are using OpenOCD [1]. We need to specify the interface and target configuration files:

openocd -f interface/stlink-v2.cfg -f target/stm32f1x.cfg

OpenOCD starts running as a server and waits for connections from clients (Telnet, GDB, RPC) and processes the commands issued through those channels.

We can try and connect to the OpenOCD server with Telnet:

telnet localhost 4444

Then we can, for example, display all registers and their values:

> reg

Or halt and re-run:

> reset halt
> reset run

Flashing

We can flash the microcontroller using OpenOCD (assuming we are already connected with telnet):

> program filename.elf verify reset

Note

The program command will automatically execute the reset init scripts, flash the image, verify it (if verify parameter is given) and run it if reset parameter is given.

Alternatively, we can launch OpenOCD and flash the program with a single command:

openocd -f interface/stlink-v2.cfg -f target/stm32f1x.cfg \
    -c "program filename.elf verify reset exit"

Binary files need the flash address to be specified:

> program filename.bin verify reset 0x08000000

Debugging

We use GDB [2] for debugging. Note that we connect to OpenOCD gdbserver using the port 3333, rather than the port 4444 used with telnet:

$ arm-none-eabi-gdb main.elf
(gdb) target extended-remote localhost:3333

Note

Remember that you can shorten the commands: tar ext :3333 is the same as target extended-remote localhost:3333.

Once we are connected, we can execute OpenOCD commands simply prepending the word monitor:

(gdb) monitor reset halt
(gdb) monitor reset run

If we want to load the .elf file, we can simply execute the load command now:

(gdb) load