So went wnt the following way to get support for STM32-Boards (like the STM32F405 on my pyboard)
in the Arduino IDE:
- Installing Arduino IDE
- getting STM32-Support via the Boardmanager and the Boards-URL
http://dan.drown.org/stm32duino/package ... index.json
- getting program/flash-Support for the STM32-Boards via the
STM32CubeProgrammer - which includes the CLI-Flash-command in the /bin directory
On my system the pyBoard is shown as COM4: (while running MicroPython) and connected via USB
I do set the Arduino IDE to a generic STM32F405RG board and the transfer-mode to DFU
Then I connect on the pyBoard 3.3V and BOOT0 for DFU-mode (COM4: goes away)
I can compile the sketch and it gets transfered to 0x8000000 (sometimes als referenced as 0x08000000) - but after the successful transfer and a reset to the pyBoard the LEDS keeping lit like in the DFU-mode and no COM-port is recognized

The only way to get the board to lige again is to flash MicroPython again via the DFU-Mode
(here I use dfu-utils under Linux) but can also try the STM32CubeProgrammer-GUI (which needs Java)
to flash the DFU-file
Has anyone successfully flashed/used a pyBoard (v1.1) with the Arduino IDE?
Is there another/special board-definition available for the Arduino IDE Boardmanager for the use with the pyBoard?