TTYs connected to an SCC port do not properly track carrier detect.  I
consider this a serious problem -- consider a situation where you're
logged in and su'd to root, you lose carrier, and some evil person
dials in and gets the line you were on.

I noticed this problem because I was trying to set up a SLIP
connection via one of the ports on my 5000/120, and sliplogin was not
getting a SIGHUP when the line dropped.

The code in scc.c has some vague comments that seem to indicate this
code was commented out to fix a problem with console handling.
However, when I enabled the code, I was able to use a serial console
with no obvious problem.  Can anyone shed some light on this?

Anyway, here's a patch to re-enable the carrier detect code.

--- /usr/src/sys/arch/pmax/tc/scc.c-orig	Wed Oct 16 20:35:19 1996
+++ /usr/src/sys/arch/pmax/tc/scc.c	Thu Apr 10 04:11:55 1997
@@ -1448,14 +1448,12 @@
 	 * Is it related to  console handling?
 	 */
 #ifndef alpha
-#ifdef	notyet	/*XXX -does this help pmax console? */
 	if (car) {
 		/* carrier present */
 		if (!(tp->t_state & TS_CARR_ON))
 			(void)(*linesw[tp->t_line].l_modem)(tp, 1);
 	} else if (tp->t_state & TS_CARR_ON)
 		(void)(*linesw[tp->t_line].l_modem)(tp, 0);
-#endif /*notyet*/
 #endif /* !alpha */
 	splx(s);
 }

--
entropy -- it's not just a good idea, it's the second law.