[fix bootloader] TFT35 bigtreetech display

Описание

Do not attempt it if not needed !
A corrupted bootloader won't allow us to update the Firmware of the display (otherwise just update your display's Firmware as steps are also described below..)

https://github.com/bigtreetech/BIGTREETECH-TouchScreenFirmware
How to reinstall the Bootloader (bios) with a CH340 debugger:
1- Download your bootloader file and FlyMcu
2- 1:19 Plug everything (5v to 5v; GND-GND; TX-RX and rx-tx) / CH340 to PC
3- 3:30 Execute FlyMcu / look for your bootloader file / look for your right "Port:COM CH340" / check "Run After ISP complete"
4- 4:03 Put the display in its "update mode" (white screen) by shorting the two pads and pressing the reset button in same time
5- 5:28 In FlyMcu click "Start ISP"

After completion, you get "illegal user App1!" (6:18)
You now understandably have to reinstall the Firmware of the display:
1- Download all the repository "Code" / Local / Download ZIP
2- Extract from the archive to the root directory of your formated SD card (FAT32)
the Firmware (BIQU_TFT35_APP1_V2.0.27.x.bin)
the config file (config.ini)
the language pack (language_en.ini)
the optional theme ("TFT35" folder which contains bmp and font inside)
3- insert the SD card to your diplay and press reset; updating process will start !
4- calibrate your display (red dot appearing at each touch ! )
5- set the correct speed of the connection between it and the main board (baud rate)
https://youtu.be/Qb-0vCZgB4A?t=11

This operation is worth doing since CH340 are cheap and quickly available anywhere.
But pay attention, the "CH340 ESP-01" has more pins if ever you plan on also programming an ESP8266 (wifi-module)