[En-Nut-Discussion] MASK and SPACE support for 9bit frame

[Henrik Maier]

Hi,

Thank you for publishing this patch.

The usart driver had already some support for 9-bit addressing. However when
we tried to use it we found that we could not control the 9th bit on a
character basis. Typically you want the first character of a frame to be
sent with the 9th bit set but not the remainder of the frame. We also found
that it lacked the receiving part. We eventually ended up writing our own
application specific 9-bit mode driver rather than using usartavr.c.
 
Does your patch makes sure that the 9th bit is only applied to the first
character of a frame and not to characters currently waiting in the uart
driver's send buffer 
and also not to subsequently written characters?

Why did you use mark/space rather than the AVR's native 9-bit mode (using
TXB8)?

Do you have also a solution for receiving 9-bit data?

Henrik