In order to make flashing tomu boards more accessible, this directory
contains information, scripts and configurations to allow flashing of the
tomu using a Raspberry Pi and two-wire debugging. While these
configurations are specifically for a Raspberry Pi, the setup should be similar
for any system that allows you to use GPIO pins and can run GNU/Linux (and
OpenOCD of course).
I'm currently working on a set of scripts to make this much simpler, but at the moment setting up your Raspberry Pi has to be done manually. This includes compiling OpenOCD from source (which can be done with the build-openocd.sh script).
The tutorial I used can be found here, though setting up networking is out of scope for that tutorial.
This installs all of the necessary configurations to use two-wire debugging to
flash a tomu. After installing OpenOCD you can flash your tomu by running
sudo openocd -f raspberrypi-native.conf -f tomu-flash.conf.
This will flash the prebuilt dfu firmware (located at /prebuilt/toboot.bin) to the tomu.
You may need to write your own interface configuration file for other devices.
Contrary to its name, two-wire debugging (or more accurately "Serial Wire
Debug") uses four wires: vcc, swdio, swdclk, and ground. Looking at the
image below of the back of the tomu, that is the left-to-right order of
solder pads. The colour coding is red=vcc, blue=swdio, green=swdclk,
square=ground.
It is not necessary to solder anything to your tomu in order to flash it. If
you have a steady hand you can just hold the wires in place for the couple of
seconds it takes to flash a board. I super-glued some breadboard wires together
to ensure the spacing is constant. You can loop openocd invocations by adding
watch in front of your flashing command. e.g. watch openocd -f ...
The pins used by the configuration files for the Raspberry Pi in this directory
for two-wire debugging are pins 24 and 25 for swdio and swclk
respectively. As far as I can tell, Raspberry Pi pin numbering is backwards
compatible, so if your Raspberry Pi has less pins than in the diagram below
just count the pins from the left. In the diagram, vcc is orange and ground
is black. Make sure you get the ordering of the pins correct or you'll end up
restarting your board (due to a short-circuit).
If you're flashing a tomu with a different board you'll need to figure out
the right pins to use on your own.
tomu can also be flashed using the ST-Link v2 programmer. The ST-Link v2 comes as part of STM Discovery and STM Nucleo boards. It can also be bought off eBay/Aliexpress/etc. for 2-5 USD in a USB Stick format.
This example uses an STM32F407 discovery board, however the interface should always be a 6-pin header with a white dot marking for the VDD side for all STM Discovery and Nucleo boards. If you have a chinese USB stick, they usually follow the layout of the 10-pin Cortex Debug Connector and you'll need to connect to the VDD, GND, SWDIO and SWDCLK pins there as well.
For wiring up the Discovery/Nucleo, follow the picture. The coloring of the pins is the same as described under Wiring. Also make sure your ST-Link selector jumpers are cleared. Note that Discovery ST-Link does not power the target MCU directly, so power has to come from the host board.
After connecting, run:
openocd -f interface/stlink-v2.cfg -f tomu-flash.conf