SCI_TDRE
#define SCI_TDxE_CLEAR (u32)(~(SCI_RESERVED | SCI_TEND | SCI_TDRE))
#define SCxSR_TDxE(port) (((port)->type == PORT_SCI) ? SCI_TDRE : SCIF_TDFE)
.poll_sent_bits = SCI_TDRE | SCI_TEND
return !(sci_serial_in(port, SCxSR) & SCI_TDRE);