you can get some hints from here
https://medium.com/@paramaggarwal/progr ... 3cec0dbc86
make sure it is a 3.3v uart dongle.
there are also some quite cost effective usb-uart dongles e.g.
https://www.aliexpress.com/wholesale?ca ... ext=cp2102
there are some subtle protocol differences which may result in getting stalled.
e.g. stm32 is expecting 8E1 line discipline (i've once noted that 8N1 works, but it may not be always that lucky, some arduino sketches don't set line disciplines, i.e. default to 8N1 in the sketch. and that specified on the command line at the pc is ignored)
https://www.st.com/resource/en/applicat ... ronics.pdf
and you need to set BOOT0
https://www.st.com/resource/en/applicat ... ronics.pdf
there are fake blue pills circulating in the market hence be wary of that too
and you'd need to see that it is after all the right 'upload method' that should be 'Serial'
normally for libmaple core the tool that interface with the com port is stm32loader, i think, i'm not sure about it too.
https://github.com/jsnyder/stm32loader
you can try using that app itself on the command line to see if you are able to achieve some success flashing the bin / firmware file.
you can try flashing one of the bins e.g. the usb dfu boot loader if you are after all using a blue pill board.
https://github.com/rogerclarkmelbourne/ ... r/binaries
the binary for blue pill normally is generic_boot20_pc13.bin
or generic_boot20_pc13_fastboot.bin
after installing the boot loader, press reset, and the led should keep blinking.
once you have this boot loader installed, you can try installing the sketch with simply a usb cable. i.e. select the upload method 'stm32duino bootloader', if you still hit issues installing a sketch, you can try setting boot1 (after you have successfully flashed the boot loader mentioned above) and try again. note, when you are using the usb cable for flashing, you should *not* set BOOT0
if you are still struggling with the atmega? uart dongle you may want to try getting a st-link v2
https://www.st.com/en/development-tools/st-link-v2.html
https://www.adafruit.com/product/2548
this is more than just a programming dongle, it is a jtag/swd dongle, hence at some point you can play with debug if you want.