uart.flush()
flush() will wait until all characters have been sent. It may return
while the last character is sent. if needed, the calling code has to
add one character wait time. To avoid a permanent lock, a timeout
applies depending on the size of txbuf and the baud rate.
ret = uart.txdone()
ret is True if no transfer is in progress. It may return True if the
last byte of a transfer is sent.
ret is False otherwise.
2488311dc2