Please help me with this C8051F340 board

Hello everybody,

I digged out a small board out of my belongings that I acquired probably 6 or 7 years ago. It has printed C8051F340 on it. I don't have any clue why I bought it neither. Only on some sites on the Internet it is called an Arduino 8051 board, but I have no clue why.

The SD card in the card reader isn't readable and gdisk says that two partitions would overlap. There are three LEDs on it that work fine. One is constantly lit and the two others flash alternatively.

I tried it from the Arduino IDE and I tried it standalone with USB as power source and connected a USB to RS232 adapter to it. The adapter creates a ttyUSB0 device and picocom detects sometimes a single character if interrupt shortly the connection to the board. So everything seems to work fine apart from this board which is mute ... Well, it has only two further chips on it apart from the 8051.

Anyone knows what the purpose of this board is?

8051 processor with RS232 interface? No ideas.