the kernel. ppp_tty.c goes to some lengths to minimise the inter-layer
calling (including a soft ISR). ppp_tty.c takes care of the soft masking
that was needed still.
(I've discovered that bugs in this area show up within an hour if the
masking was not correct.. :-} This combination has proven stable on
specialix serial ports, although there was some concern about the softtty
parts of sio/cy and netisr colliding - but Bruce has fixed that now)
7dbdd057a4