How to reinstall (restore) manufacturer`s bootloader on STM32F103C8T6 development board?

[AMelk]

I have STM32F103C8T6 development board (like this: https://www.rogerclark.net/wp-content/uploads/2014/11/STM32Mini.jpg) which can be programmed by USB interface. I programmed it several time before, but now I can't do this. When I connect it to the PC, I get a warning messege (pinned) and can't load firmware to the STM.

[Tesla DeLorean]

The ST boot loader is in ROM, strap BOOT0 high to enter it.

People call this the "Blue Pill"

Still doesn't work, perhaps review voltages on supplies, and behaviour of NRST pin. Try using a SWD/JTAG in "Connect Under Reset" mode, where you connect SWDIO, SWCLK, NRST, GND

[AMelk]

Thanks for reply. I can program my STM32 board by external ST-Link V2 programmer, but USB interface is doesn't working.

[AMelk]

And all voltages is normal. On NRST pin is 3.3V.

[Tesla DeLorean]

USB doesn't report as "STM32 DFU MODE" (or whatever) when BOOT0 is high at power on/reset, or your code running doesn't support USB?

You could have broken/damaged the port and or cable.

[AMelk]

When I loading empty code (with empty cycles while() and int main()) by external programmer St-Link V2 - usb bootloader still not working.

[Tesla DeLorean]

The code you're loading should be irrelevant is BOOT0 is HIGH.

Attempt to isolate the issue to the board by changing USB port, USB cable, or PC

[turboscrew]

Blue pill can't be programmed with USB unless you put an USB-bootloader in it. I wonder if there has been STM32duino USB bootloader in it. The only manufacturer-made bootloader in it is RS-bootloader.

https://wiki.stm32duino.com/index.php?title=Burning_the_bootloader

[AMelk]

Thanks for reply. It's a new board. All that I was do - it load blink code (​then it worked). I did nothing with bootloader. I was try to connected board to the another PC, by another usb cable, but it's still not working🙁

[turboscrew]

Where did you got it? If it's from STM32DUINO-related place, it may have USB-bootloader preinstalled. STM doesn't put USB-bootloader in F103s.

Check table 3 here...

https://www.st.com/content/ccc/resource/technical/document/application_note/b9/9b/16/3a/12/1e/40/0c/CD00167594.pdf/files/CD00167594.pdf/jcr:content/translations/en.CD00167594.pdf