Just buy ST-LINK2 on aliexpress:
it allows to flash STM32 even if it is bricked. You will need to connect GND=GND, VDD=3.3V, SWDIO=SWDIO, SWCLK=SWCLK. These signals are placed near boot jumper on the right side of nanoVNA.
In order to flash you will need ST-LINK Utility:
Connect ST-LINK to NanoVNA, start ST-LINK Utility, and set the following values in the window:
Address: 0x08000000
Size: 0x20000
Data width: 8 bits
After that select menu: Target => Connect, it should connect to STM32 and show it's memory content.
Use File => Open file menu to open HEX file with NanoVNA firmware.
And then flash it into NanoVNA with menu Target => Program and verify
That's it :)
See HEX file with NanoVNA firmware in attachment.
