Re-programming the CH559 device
Hold down the button and plug in the device into your PC. You can simply run the “compile.bat” and it will compile the source and upload it to the device. The device will then disconnect from USB.
uart.c sendHidPollMSG function is where most of the interesting things happen. You may need a serial USB adapter (TX/GND pins on the board) so you can see what the CH559 device is sending to the AVR which goes to the GB.
By default, it seems that USB keyboards send the same character over and over again until you let go and then it sends a 0. We added some code to the sendHidPollMSG function to only send the button pressed.