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Nucleo32 board preparation

Additional steps are required to run the firmware on the Nucleo32 board.

USB-A cable

Board does not provide an USB cable / socket for the target MCU communication. Own provided USB plug has to be connected in the following way:

PIN / Arduino PIN MCU leg USB wire color Signal
D10 / PA11 21 white D-
D2 / PA12 22 green D+
GND (near D2) ------- black GND
not connected ------- red 5V

Each USB plug pin should be connected via the wire in a color defined by the standard. It might be confirmed with a multimeter for additional safety. USB plug description:

PIN USB wire color Signal
4 black GND
3 green D+
2 white D-
1 red 5V

See this USB plug image, and Wikipedia's USB plug description.

Plug in USB-A_schematic.pdf has wrong wire order, registered as solo-hw#1.

The power is taken from the debugger / board (unless the board is configured in another way). Make sure 5V is not connected, and is covered from contacting with the board elements.

Based on USB-A_schematic.pdf.

Firmware modification

Following patch has to be applied to skip the user presence confirmation, for tests. Might be applied at a later stage.

diff --git a/targets/stm32l432/src/app.h b/targets/stm32l432/src/app.h
index c14a7ed..c89c3b5 100644
--- a/targets/stm32l432/src/app.h
+++ b/targets/stm32l432/src/app.h
@@ -71,6 +71,6 @@ void hw_init(void);
 #define SOLO_BUTTON_PIN         LL_GPIO_PIN_0

-#define SKIP_BUTTON_CHECK_FAST              0
+#define SKIP_BUTTON_CHECK_FAST              1


It is possible to provide a button and connect it to the MCU pins, as instructed in USB-A_schematic.pdf:

PA0 / pin 6 --> button --> GND

In that case the mentioned patch would not be required.

Development environment setup

Environment: Fedora 29 x64, Linux 4.19.9

See for the original guide. Here details not included there will be covered.

Install ARM tools Linux

  1. Download current ARM tools package: gcc-arm-none-eabi-8-2018-q4-major-linux.tar.bz2.

  2. Extract the archive.

  3. Add full path to the ./bin directory as first entry to the $PATH variable, as in ~/gcc-arm/gcc-arm-none-eabi-8-2018-q4-major/bin/:$PATH.

Install ARM tools OsX using brew package manager

brew tap ArmMbed/homebrew-formulae
brew install arm-none-eabi-gcc

Install flashing software

ST provides a CLI flashing tool - STM32_Programmer_CLI. It can be downloaded directly from the vendor's site: 1. Go to download site URL, go to bottom page and from STM32CubeProg row select Download button. 2. Unzip contents of the archive. 3. Run *Linux setup 4. In installation directory go to ./bin - there the ./STM32_Programmer_CLI is located 5. Add symlink to the STM32 CLI binary to .local/bin. Make sure the latter it is in $PATH.

If you're on OsX and installed the STM32CubeProg, you need to add the following to your path:

# ~/.bash_profile
export PATH="/Applications/STMicroelectronics/STM32Cube/STM32CubeProgrammer/":$PATH

Building and flashing


Please follow, as the build way changes rapidly. Currently (8.1.19) to build the firmware, following lines should be executed

# while in the main project directory
cd targets/stm32l432
make cbor
make build-hacker DEBUG=1

Note: DEBUG=2 stops the device initialization, until a serial client will be attached to its virtual port. Do not use it, if you do not plan to do so.

Flashing via the Makefile command

# while in the main project directory
# create Python virtual environment with required packages, and activate
make venv
. venv/bin/activate
# Run flashing
cd ./targets/stm32l432
make flash
 # which runs:
 # flash: solo.hex bootloader.hex
 #  python solo.hex bootloader.hex all.hex (intelhex library required)
 #  STM32_Programmer_CLI -c port=SWD -halt -e all --readunprotect
 #  STM32_Programmer_CLI -c port=SWD -halt  -d all.hex -rst

Manual flashing

In case you already have a firmware to flash (named all.hex), please run the following:

STM32_Programmer_CLI -c port=SWD -halt -e all --readunprotect
STM32_Programmer_CLI -c port=SWD -halt  -d all.hex -rst



Project-provided tests.

Simulated device

A simulated device is provided to test the HID layer.

make clean
cd tinycbor
cd ..
make env2
# run simulated device (will create a network UDP server)
# run test 1
./env2/bin/python tools/
# run test 2 (or other files in the examples directory)
./env2/bin/python python-fido2/examples/

Real device

# while in the main project directory
# not passing as of 8.1.19, due to test solution issues
make fido2-test


FIDO2 test sites


U2F test sites


FIDO2 standalone clients


USB serial console reading

Device opens an USB-emulated serial port to output its messages. While Nucleo board offers such already, the Solo device provides its own.

  • Provided Python tool
python3 ../../tools/ monitor /dev/solokey-serial
  • External application
sudo picocom -b 115200 /dev/solokey-serial

where /dev/solokey-serial is an udev symlink to /dev/ttyACM1.


Dumping firmware

Size is calculated using bash arithmetic.

STM32_Programmer_CLI -c port=SWD -halt  -u 0x0 $((256*1024)) current.hex

Software reset

STM32_Programmer_CLI -c port=SWD  -rst

Installing required Python packages

Client script requires some Python packages, which could be easily installed locally to the project via the Makefile command. It is sufficient to run:

make env3