_ao_usart_rx(usart, is_stdin);
if (!_ao_usart_tx_start(usart))
_ao_usart_rx(usart, is_stdin);
if (!_ao_usart_tx_start(usart))
ao_serial_set_sw_rts_cts(struct ao_stm_usart *usart,
void (*isr)(void),
struct stm_gpio *port_rts,
ao_serial_set_sw_rts_cts(struct ao_stm_usart *usart,
void (*isr)(void),
struct stm_gpio *port_rts,