How to deal with the situation cannot download?

There are many reasons for this problem:

1. Check basics, such as power supply, board type and COM port.

2. Bluetooth will occupy the serial port which will hamper uploading. Please disconnect the current Bluetooth connection, and try again.

3. The device serial port may be occupied. Please disconnect all peripherals then recompile and download again.

4. Arduino IDE may crashed. Please disconnect all Bluetooth (include smartphone), close all Arduino IDE software, pull USB line, reopen and test.

5. Bootloader in the FireBeetle 328P may get lost. Please try re-uploading Bootloader of ATmaga328p.

6. BLE 4.1 firmware may wrong. Please re-upload firmware and check the former chapter for reference.