Black Magic Probe from a Blue Pill

This chapter describes the process of making a Black Magic Probe from a Blue Pill board. The steps were tested on Ubuntu 18.04.3 LTS and Arch Linux 5.3.7.

Preparation

The process requires the following packages to be installed:

$ sudo apt install build-essential \
                   curl \
                   dfu-util \
                   gcc-arm-none-eabi \
                   gdb-multiarch \
                   git \
                   python \
                   python-pip

or on Arch Linux:

$ sudo pacman -S curl \
                 dfu-util \
                 git \
                 python \
                 python-pip
$ yaourt -S arm-none-eabi-gcc \
            gdb-multiarch

It is convenient to join the dialout group. This way you will not need super-user privileges to work with BMP and USB-to-UART adapter:

$ sudo adduser $(id -un) dialout

or the uucp group on Arch Linux:

$ sudo gpasswd -a $(id -un) uucp

In order for the group change to take effect, you will need to re-login.

Get the stm32loader script and install its python dependencies:

$ git clone https://github.com/jsnyder/stm32loader
$ pip install pyserial

Get the BMP firmware:

$ git clone https://github.com/blacksphere/blackmagic
$ cd blackmagic
$ git submodule update --init --recursive

BMP repository provides udev rules for the probe. The rules instruct udev to symlink the GDB endpoint to /dev/ttyBmpGdb and the UART to /dev/ttyBmpTarg. Also they allow to upgrade BMP firmware without super-user permissions.

$ sudo cp driver/99-blackmagic.rules /etc/udev/rules.d/
$ sudo udevadm control --reload-rules

Building

Correct probe host should be selected. In our case it's swlink.

$ make PROBE_HOST=swlink

Building

This will produce two binaries we are interested in: src/blackmagic_dfu.bin and src/blackmagic.bin. The first is a bootloader, which will be flashed with the USB-to-UART adapter. And the second is the actual firmware, which will be loaded through USB with help of the bootloader.

Flashing Bootloader

Connect the USB-to-UART adapter with the Blue Pill according to this table:

USB-to-UART Blue Pill

GND GND

RXD A9

TXD A10

Warning: Don't connect any power source now. We will power up the board through USB at the step 5. Using USB together with 5V or 3.3 pins can damage your board.
Set the jumper on the USB-to-UART adapter to the position where VCC and 3V3 are shorted. This will set the adapter's output voltage to 3.3 v. Although it is not strictly needed, because A9 and A10 pins are five-volt-tolerant.
Set BOOT0 jumper on the Blue Pill to 1 to boot into the factory programmed bootloader. The bootloader is responsible for programming the board through UART.

USB-to-UART	Blue Pill
GND	GND
RXD	A9
TXD	A10

CH340G connected to Blue Pill

Before connecting the USB-to-UART adapter to your PC, open the system journal:
```
$ journalctl -f
```
Connect the USB-to-UART adapter and notice the name it is assigned:

CH340G in journal

Connect a USB-cable to the Blue Pill and start the flashing process. Replace /dev/ttyUSB0 with your value from the previous step. If the process is not starting, press the reset button on the Blue Pill.
```
$ ../stm32loader/stm32loader.py -p /dev/ttyUSB0 -e -w -v src/blackmagic_dfu.bin
```

Successful load

Set BOOT0 jumper on the Blue Pill back to 0.

Reset Blue Pill jumpers

Flashing Firmware

Now you can disconnect the USB-to-UART adapter from the Blue Pill and your PC. The firmware will be flashed through USB port:

$ dfu-util -d 1d50:6018,:6017 -s 0x08002000:leave -D src/blackmagic.bin

Successful load

Now we will check that it works. Reconnect the Blue Pill and open a GDB session:

$ gdb-multiarch

At the GDB prompt enter the following commands:

target extended-remote /dev/ttyBmpGdb
monitor version

GDB check

If your output is similar to the output above, congratulations! Now your Blue Pill is a Black Magic Probe! Next time you need to upgrade the firmware you only need to repeat the dfu-util command above.