tty parity

[utzoo!duke!phs!dennis]

The reflection of the parity error to the user is the non-echo of
the input character.  It would be trivial to alter the drivers to
echo a BEL or whatever you want; in fact, this character can be
added to the special character table (struct tc).  A multiple-
character string (like <\007\007PARITY ERROR -- REENTER
LINE\007\007\r\n> to quote a nasty system) would be more diffi-
cult.

Note that this would entail adding the special character to the
output queue in the interrupt routine; something that isn't very
pretty, but certainly isn't difficult (you have the pointer to
the tty structure already in hand, so to speak).  You can add as
much intelligence as you want (ie, checking the character count,
checking echo status, and so forth), but be sensible.