So it blocks until the serial output buffer is flushed by the natural process.
Oh! it's a blocking process, I see. Do you know if it "pass the tag" to another process If we use DUE scheduler? I just can't wait to receive my DUE. 
So many thing to try, so many answer to gather.
This is useful when implementing half duplex communications on the serial port.
Yeah it's great for EIA-485/RS-485 2 wires com.
Mk, so i'm happy to have read that post, I've learn new stuff today. Thank you Mike.