UART_DM_TFWR
volatile uint32_t * UART_DM_TFWR = (uint32_t *)(UART_BASE + 0x1c);
*UART_DM_TFWR = UART_DM_TFW_VALUE;
uart_setreg(bas, UART_DM_TFWR, UART_DM_TFW_VALUE);