Serial flashing method

Caution

Warning! Using serial flashing requires doing micro soldering to the pin(s) of gd32, please use the SWD flashing method if you are not comfortable doing it!)

Usage

In the following cases, you might want to use serial for flashing your board:

The SWD GPIO (PA13 PA14) is used as a GPIO, thus SWD is disabled
You do not have a STlink V2 or any compatible SWD debug probe
You want to use STM32 Cube Programmer
Flash unlock fails

Wiring

T1he gd32/stm32/mm32 bootloader is activated by pulling BOOT0 HIGH and BOOT1 LOW

The Serial pin in bootloader mode is different from the normal ones (pa9 TX pa10 RX)

GPIO	Description	wiring
BOOT0	--	connect to 3.3V
PB2	BOOT1	connect to GND with 1K resistor
PA9	TX	RX
PA10	RX	TX
VCC		3.3V
GND		GND

serial flash

On most board, the BOOT0 is directly soldered to GND pad, so you will have to lift the pin up with a sharp tool while heating it
BOOT0 can be directly connected to 3.3v afterwards, just make sure there is no short circuit to GND from the pad it originally connect to
BOOT1 must be pulled LOW through a 1K resistor, because it is used as a normal GPIO, if you hard pull it to GND it can cause a short circuit in the micro controller and destroy it, and if you use too high value it can get dragged by the load to HIGH
TX and RX is PA9 PA10 which is always used by the motor blue and green phase, so you can solder the line to the gate driver ic they will not interfere with the signal and makes a larger solder pad to work with
It is important never connect the battery when serial line is connected, because you can create a short circuit with the mosfets, power the board from CP2102 internal 3.3v source is enough (100ma)
Make sure the usb to serial adapter is 3.3v not 5v(and also not +-15v!), or at least have a series resistor, otherwise it will not work I tried

video toturial of soldering: https://youtu.be/rUMzHYvKoW4