I've built a couple of small PCBs with different ST Micro STM32 MCUs on them, such as my STM32F072 breakout board. These boards need some kind of firmware to do something useful.
ChibiOS-RT is a small RTOS which has support for most STM32 MCUs, including a USB stack which can make the MCU appear as a virtual COM port (CDC ACM) on both Windows and Linux. This means that ChibiOS makes it very easy to start actually doing something with the hardware I've built.
This project is a collection of small test firmwares for the PCBs I've designed and built. It's nothing fancy, most firmwares just blink a LED and start up a virtual COM port where one can use the built in "shell" to run small commands on the device.
It's very easy to extend the ChibiOS shell with new commands, making it possible to quickly verify that a piece of hardware is working the way it should.
Get a STM32F072 breakout board. You'll probably have to have someone else manufacture the naked PCB for you but you should be able to solder the components yourself. The STM32F072 MCU and the USB connector can be a bit tricky to solder, but other than that there are only a dozen small components needed.
Install a recent version of Ubuntu Linux on a PC. Personally I use Linux Mint 17.2 which based on Ubuntu 14.04. If you run Windows or OSX the easiest way to get started is probably to install Ubuntu in a virtual machine, but I'm not sure if it will be program the board over USB using a virtual machine.
When you have installed Ubuntu, start a terminal and make sure the system is up to date:
sudo apt-get update
sudo apt-get upgrade
Install some tools and libraries needed by this project:
sudo apt-get install git automake autoconf make pkg-config libusb-1.0-0-dev
Install a toolchain, that is, a C compiler, linker, C library and some other tools needed to build applications for Linux:
sudo apt-get install gcc binutils libc6-dev
Install a toolchain for ARM needed to build applications for the ARM core in the STM32 MCU:
sudo apt-get install gcc-arm-none-eabi libnewlib-arm-none-eabi
Use git to download a copy (clone) of the source code from github:
git clone https://github.com/wingel/chibios-stm.git
Use git to download the source code for some other projects (submodules) this project depends on:
cd chibios-stm
git submodule init
git submodule update
Build dfu-util which is needed to program a STM32 device over USB:
cd dfu-util
./autogen.sh
./configure
make
cd ..
Build the firmware for the STM32F072 breakout board:
cd stm32f072-breakout
./build.sh
Connect the STM32F072 breakout board to your PC. Put it in Device Firmware Update (DFU) mode by keeping the BOOT button pressed while pressing and releasing the RESET button.
If you look at the kernel logs.
dmesg | tail
You should see some messages about new a USB device like this:
usb 4-1.2: New USB device found, idVendor=0483, idProduct=df11
usb 4-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 4-1.2: Product: STM32 BOOTLOADER
usb 4-1.2: Manufacturer: STMicroelectronics
usb 4-1.2: SerialNumber: FFFFFFFEFFFF
Start the programming with:
./prog.sh
When the programming has finished the board should reboot and the blue LED should start blinking. If you want make sure that it really is your new firmware that's running, modify "main.c" and change the chThdSleepMilliseconds delays in the "blink" thread function at the beginning of the file, build and program the board again and verify that the blink rate changes.
If you look at the kernel logs now the board should also show as a USB virtual COM port named ttyACM-something:
usb 4-1.2: New USB device found, idVendor=0483, idProduct=5740
usb 4-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 4-1.2: Product: STM32
usb 4-1.2: Manufacturer: STMicroelectronics
usb 4-1.2: SerialNumber: 000000000000000000000000
cdc_acm 4-1.2:1.0: ttyACM3: USB ACM device
Start a terminal program and connect to the virtual COM port. I usually use my own little terminal program for Linux, tt, but you could also use minicom or Putty which is available for both Linux and Windows. You can now start issuing commands to the ChibiOS shell, for example, try the "help" or "info" commands:
ChibiOS/RT Shell
ch> help
Commands: help exit info systime reset
ch> info
Kernel: 3.0.2
Compiler: GCC 4.8.2
Architecture: ARMv6-M
Core Variant: Cortex-M0
Port Info: Preemption through NMI
Platform: STM32F072xB Entry Level Medium Density devices
Board: ST STM32F072B-Discovery
Build time: Aug 24 2015 - 21:14:14
ch>
You can now start extending the firmware with new commands. To see how to do this, open at main.c and look at the function "cmd_reset" and the "commands" table. For example, to see an example on how to extend the stm32f072-breakout code to interface with a DHT11 or DHT22 temperature sensor, look at the stm32f072-breakout-dht directory.