How to use ttyS0?

Hi, everyone.

I have a board using AM1808 made by some company which is not available now.

I am porting linux 2.6.3 kernel.

I have a circuit diagram of the board.

In the board, UART1/2 are used for debug and RS-485.

But UART0 is assigned to WiFi daughter board connector.

I think UART0 pin may be assigned for WiFi connection.

I checked by inputing "echo asdjfkdsf > /dev/ttyS0" by console, no signal on UART0 pin.

How can I check this UART0 RX/TX pins are assigned to which function?

How can I assigned UART0 RX/TX pins for UART0?

I don't have a plan to use WiFi function.

Kernel? or u-boot?

BR

Paul