[Gllug] Sun Sparcstation - disconnecting serial console causes BREAK

[John Edwards]

On Fri, Aug 12, 2005 at 10:30:16AM +0100, Nix wrote:
> On Thu, 11 Aug 2005, Ian Northeast suggested tentatively:
<snip>

>> I forget who mentioned that unplugging the serial cable sends a
>> break. It doesn't usually, about 1 time in 4 IME. It depends on
>> exactly how the pins disconnect, which is unpredictable.
> 
> My problem is that rebooting PCs sends a break down attached serial
> lines, so I can't leave the serial cable plugged in from the Sun,
> which means that in case of serious oops-can't-reboot-into-default-
> kernel buggerups, when working remotely, I'm stuffed.
> 
> It's a dilemma. Leave the cable in and PC reboots kill the Sun, and
> 'cos it's serves all the home directories I have trouble getting back in
> to do a `go'; take it out and severe buggerups on the Sun are
> unfixable.

How are you with a soldering iron ?

This is related to the "disconnect causes BREAK", and can be fixed by 
placing a resister between pins 3 and 25 on a DB25 serial connection.

>From the "Using a Terminal as Console" in the "Sun Hardware Reference":

Unfortunately, turning off the terminal or disconnecting it is usually 
interpreted as a BREAK and halts the machine. Thus, it is not easily 
possible to turn off the terminal when the console is not in use, or 
to use one terminal with many machines via a switchbox.  Suggested 
solutions include a special cable (on a 4/2xx CPU, a 4.7K resistor 
between pins 3 and 25 may work) or modifying the SunOS serial driver 
(zs) to ignore breaks.

At Brunel Uni this was included in a little custom built DB25-RJ45 
adapter. People like RS will sell DB25-DB25 adapters with enough 
space for a resister and cables. 


>> single cable between 3 Suns and it works fine. You unplug it, then
>> check that the Sun in question still works. If it doesn't you were
>> unlucky and it saw a break
> 
> FWIW, I've never had a cable unplug send a break; maybe it's machine-
> specific, or maybe I've just been very lucky.

I've certainly seen it on SparcStations, maybe Sun fixed this by the 
time of the Netra.


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|    John Edwards   Email: john at cornerstonelinux.co.uk    |
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