Arduino for STM32

Found it. In the STM32CubeProgrammer I have to set:

- top right type-dropdown "ST-LINK"
- Port "SWD"
- Mode "HotPlug"
- Reset mode "Software Reset"
- Speed "Fast"
- Shared "enabled" this is the key setting

With the ST-Link not connected to USB clicking the top right Refresh icon the Serial Number ...

So has anyone got an idea what the encountered error message actually wants to tell me ?

But whgat does the message say? I've no idea what a "UR connection" and what the HWrst (HerdWare Reset?) mode is.
"is defined" where?

I want the "hot debug mode", e.g. program is running on the chip, and w/o any reset
I'd like to "attach" to the running chip, watch / stop / continue executiong ...

ST_link V2 is setup, latest Firmware flashed, but I still get just the weird message "UR connection mode is defined with the HWrst reset mode" when trying to connect, google is almost empty for the search phrase.

This message happens when
- the WeAct dummy pgm is running after a reset,
- as well ...

Even weirder: on my ZOTAC PC WeAct Black Pill conencted to the USB3 Port the simple STM Bootloader activision (holding down boot0 while hitting reset) WORKS! :shock: :shock: :shock:

The process is :
- hook up WeAct to USB port
- fire up STM CubePorgrammer, set to usb in top right corner of the ...

F*$!* different PC, same USB cable, WeAct BlackPill V3.1 autostart pgm cyclically dims and brightens LED,so far so old.
Pressing KEY for ~3 Seconds results in LED going off and USB TreeView showing STM Booloader Decive 0x483/0xDF11 appearing, BTDT.

But this time the Devices stay accessible, it ...

well if it is a *real* stm32f4xx, then I'd expect USB DFU to be just threre, i.e. that button dance sequence would simply put it in DFU mode ready to update flash using DFU. no need for uart whatsoever.
All nice an fine, but the real question is:

- which pins of a WeAct F411 BlackPill need pull ...

for f4xx I won't bother with a custom bootloader, it takes flash memory and it takes the traditional 0x8000000 start of flash address.
and much less fuss bothering with custom bootloaders e.g. that your sketch is compiled for an incompatible address etc.
you would more than likely need a custom ld ...

Connect PA9 to GND with resistor (eg. 10k) and try to reset it into DFU.
Interesting thought! But are you sure about PA9 ? That's USART1 TXD, a serial transmit pin e.g. outgoing pin, right?

AN2606 https://www.st.com/resource/en/application_note/cd00167594-stm32-microcontroller-system-memory-boot ...

Maybe. But the STM bootloader is in ROM. Only ST can fix that and it would only work in new devices.