🚀 go-pugleaf

We a have terminals connected to the psp - planar serial port RS232C interface.
The terminal attached to the `S2' port usually displays the following prompt:

Academic Information Systems 4.3 (unix) (ttys0)

login: 

and permits me to `login' and work.  But eventually, output to the terminal
will suddenly stop.  And I will not be able to restart it from the terminal.
I can login from another workstation and kill the terminal session.  But the
process remains in an `<exiting>' condition:

unix% ps -gx
  PID TT STAT  TIME COMMAND
  695 p0 S     0:00 -csh (csh)
  716 p1 R     0:00 ps -gx
  704 s0 S     0:00 -csh (csh)
unix% kill -9 704
unix% ps -gx
  PID TT STAT  TIME COMMAND
  695 p0 I     0:00 -csh (csh)
  717 p1 R     0:00 ps -gx
  704 s0 S     0:00 <exiting>
unix% 

And I cannot use the terminal again unless I reboot or enter something on
the terminal attached to the `S1' port.  Then that terminal will freeze
until I enter something on the terminal attached to the `S2' port again
which will in turn freeze and so on.  This behavior will continue until 
I reboot the system.

I would appreciate any advice I can get to help me solve this problem.
The following information may be useful:

unix% stty everything
new tty, speed 19200 baud, 32 rows, 80 columns
even odd -raw -nl echo -lcase -tandem tabs -cbreak 
crt: (crtbs crterase crtkill ctlecho) -tostop 
-tilde -flusho -mdmbuf -litout -pass8 -nohang 
-pendin -decctlq -noflsh 
erase  kill   werase rprnt  flush  lnext  susp   intr   quit   stop   eof
^?     ^X     ^W     ^R     ^O     ^V     ^Z/^Y  ^C     ^\     ^S/^Q  ^D     
unix% cat /etc/motd
4.3 BSD UNIX (6151) #1: Thu Jul 27 15:00:42 PDT 1989

Thanks in advance, Bob Tisdale (edwin@maui.cs.ucla.edu)