Building solo

To build, develop and debug the firmware for the STM32L432. This will work for Solo Hacker, the Nucleo development board, or your own homemade Solo.

There exists a development board NUCLEO-L432KC you can use; The board does contain a debugger, so all you need is a USB cable (and some udev rules).


Install the latest ARM compiler toolchain for your system. We recommend getting the latest compilers from ARM.

You can also install the ARM toolchain using a package manager like apt-get or pacman, but be warned they might be out of date. Typically it will be called gcc-arm-none-eabi binutils-arm-none-eabi.

Install solo-python usually with pip3 install solo-python. The solo python application may also be used for programming.

Obtain source code and solo tool

Source code can be downloaded from:

solo tool can be downloaded from:

  • from python programs repository pip install solo-python
  • from installing prerequisites pip3 install -r tools/requirements.txt
  • github repository: repository
  • installation python enviroment with command make venv from root directory of source code


Enter the stm32l4xx target directory.

cd targets/stm32l432

Now build Solo.

make build-hacker

The build-hacker recipe does a few things. First it builds the bootloader, with signature checking disabled. Then it builds the Solo application with "hacker" features enabled, like being able to jump to the bootloader on command. It then merges bootloader and solo builds into the same binary. I.e. it combines bootloader.hex and solo.hex into all.hex.

If you're just planning to do development, please don't try to reprogram the bootloader, as this can be risky if done often. Just use solo.hex.

Building with debug messages

If you're developing, you probably want to see debug messages! Solo has a USB Serial port that it will send debug messages through (from printf). You can read them using a normal serial terminal like picocom or putty.

Just add DEBUG=1 or DEBUG=2 to your build recipe, like this.

make build-hacker DEBUG=1

If you use DEBUG=2, that means Solo will not boot until something starts reading its debug messages. So it basically waits to tether to a serial terminal so that you don't miss any debug messages.

We recommend using our solo tool as a serial emulator since it will automatically reconnect each time you program Solo.

solo monitor <serial-port>

Linux Users:

See issue 62.

Building a Solo release

To build Solo

If you want to build a release of Solo, we recommend trying a Hacker build first just to make sure that it's working. Otherwise it may not be as easy or possible to fix any mistakes.

If you're ready to program a full release, run this recipe to build.

make build-release-locked

This outputs bootloader.hex, solo.hex, and the combined all.hex.

Programming all.hex will cause the device to permanently lock itself. This means debuggers cannot be used and signature checking will be enforced on all future updates.

Note if you program a secured solo.hex file onto a Solo Hacker, it will lock the flash, but the bootloader will still accept unsigned firmware updates. So you can switch it back to being a hacker, but you will not be able to replace the unlocked bootloader anymore, since the permanently locked flash also disables the DFU. Read more on Solo's boot stages.