Nano fire 2 uart transmit error

Hi everbody,
I'm using nano pi fire 2 uart with minicom. Receive is ok ,but transmit is
not work from nano. I tried all ports but ı took same error.When
ı send a byte from anywhere,nano pi can take,but when ı send a
byte from nano ,transmit does not work.Can you help me for this problem?

    The nanopi 2 fire has a serial demo in android system that friendlyelec
provided ,you can refer the demo to test the serial.

    You can clone the code in github: git clone 
     In nanopc-t3 ,the serial's device name is as UART3->/dev/ttySAC3.

Attention,you need to use system permissions when running the serial demo.