source: rtems/c/src/lib/libbsp/lm32/milkymist/Documentation/uart.txt @ 8affb5a9

Initialization : 

        set the CSR_UART_DIVISOR to the correct VALUE,
        depending on the internal frequency of the LatticeMico32 softcore.

        for the ML401 board, this value is calculated using this formula : clk_frequency/230400/16
        clk_frequency  = 100000000 Hz
        => we must set CSR_UART_DIVISOR to 27

How to send a byte to uart : 

void writechar(char c)
{
                CSR_UART_RXTX = c;
                while(!(irq_pending() & IRQ_UARTTX));
                irq_ack(IRQ_UARTTX);
}

How to receive a byte from uart : 


char readchar()
{
        char c;
        while(!(irq_pending() & IRQ_UARTRX));
        irq_ack(IRQ_UARTRX);
        c = CSR_UART_RXTX;
        return c;
}