Although uart_event.size and uart_event.timeout_flags fields are
meaningless to events other than UART_DATA, fix the values to 0 could
help reduce confusion.
Closes https://github.com/espressif/esp-idf/issues/12299
Increase LP_UART_EMPTY_THRESH_DEFAULT value to 4. The original value
could cause the FIFO become empty before filling next data into the FIFO
when the buadrate is high. TX_DONE interrupt would raise before actual
transmission complete in such case.
Song Ruo Jing
LiPeng
morris
gaoxu
laokaiyao