Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!rice!sun-spots-request
From: ames!ultra!!beau@uunet.uu.net
Newsgroups: comp.sys.sun
Subject: Re: TTY Sun terminal Crashes: WANTED fix if available
Keywords: Miscellaneous
Message-ID: <4497@brazos.Rice.edu>
Date: 29 Jan 90 20:41:08 GMT
Sender: root@rice.edu
Organization: Sun-Spots
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Approved: Sun-Spots@rice.edu
X-Refs:  Original: v9n10
X-Sun-Spots-Digest: Volume 9, Issue 15, message 5 of 20

In article <4335@brazos.Rice.edu> elel@cbnewsd.att.com (eric.edberg) writes:
>X-Sun-Spots-Digest: Volume 9, Issue 10, message 17 of 22
>
>Our Sun hosts (or rather some of them) are connected to ASCII terminals
>rather than the typical Sun console.  A well known problem occures if the
>BREAK key is depressed or the terminal is powered down: the system will
>crash.  At one time I heard someone talk about a fix (circuit board) that
>might prevent the crashes from occuring.  Does such a device exist ??  Is
>there really a solution to this problem ??  Just checking for solutions.
>Please post results as many would be interested.

The system does NOT crash.  The BREAK key on an ASCII console, powering UP
(not down) an ASCII console, and plugging IN the Sun keyboard (not
unplugging) all have the same effect.  These actions cause the serial
input chip to detect a framing error on the serial input line, and report
that to the kernel with an interrupt.

The serial port driver for the console serial port treats a framing error
as equivalent to the "L1-a" combination on the Sun keyboard.  The driver
aborts Unix (SunOS) and transfers control to the PROM monitor.  (The
"L1-a" combination is actually detected by the keyboard driver, one level
higher.)

At that point, one can continue the system using the "c" PROM monitor
command.

While it's easy to recover from the situation, the power-on part can be
annoying.  One "fix" for that is to install a small resistor (about 4.5k,
1/4-watt) between ground and receive data pin inside the terminal cable
connector, at the CPU end of the cable.  This "fix" also works to
eliminate the noise that causes garbage logins to appear, when a very long
terminal cable runs out to a powered-down ASCII terminal.  -- 

Beau James				beau@Ultra.COM
Ultra Network Technologies		{sun,ames}!ultra.com!beau