As I wrote last time, I have bricked my NAS due to the upgrade to a new firmware. I had to start with debugging over the serial console. I have couple of RaspberryPis laying around. One of my RaspberryPi 2 had enabled a serial port from a previous project. The great thing is that NAS board Gemini and RaspberryPi are both on same voltage levels (3.3V) for I/Os ports, so they do not need any level shifter or converter, just 3 wire cable to be able to communicate via serial (UART).
Boards data lines cannot be connected before reset, otherwise NAS would not boot up. The connection has to be established straight away after the reset and in opened terminal on the Raspberry PI the Ctrl+C keys must be hit within 3 seconds form the reset to interrupt the normal booting sequence and launch the Red-boot interface.
Three wires are needed in order to connect the boards:
|#2||RX (green)||#8||TXD0 (GPIO14)|
|#3||TX (yellow)||#10||RXD0 (GPIO15)|