UART_DIV_MAX
port->uartclk / 16 / UART_DIV_MAX,
port->uartclk / 16 / UART_DIV_MAX,
while (quot > UART_DIV_MAX) {
min = port->uartclk / 16 / UART_DIV_MAX >> 1;
min = port->uartclk / 16 / UART_DIV_MAX;