So there are three USB modes:
- Power off and connect USB - STM32 Bootloader
This one will need drivers (first one is recommended)
DFU Flashes both the bootloader and the firmware. Using this firmware file:opentx-x9d-afhds3-eu-en-2.3.14-otx.bin
Don't forget to choose X9D (and not X9D+, as I did accidentally)
2. Hold the lower trims inwards and power on - OpenTX bootloader
This would be the regular mode, when you use OTX Companion and this flashes the firmware only - not the bootloader
3. Last mode is Joystick basically
Flashing the internal RF module
1. Download the file "XJT_ACCST_2.1.0_LBT.frk", put in in FIRMWARE folder on the SD card.
2. Hold down "MENU" and go to page 2/7, scroll down to FIRMWARE folder, choose the file above.
3. Hold "ENT" and choose "Flash internal module" and press "ENT" again