On Tue, 4 Jan 2005 18:15:59 -0500 (EST)
"Greg A. Woods" <woods@weird.com> wrote:

> [ On Wednesday, December 29, 2004 at 10:35:11 (+0000), Michael Smith
> wrote: ]
> > Subject: 2.0 on DEC3000 drops to debugger if console is not
> > connected (resend)
> >
> > If I start the system with the console connected everything goes
> > OK. But if I start with the pc turned off, or with the console cable
> > disconnected the system goes to a debugger prompt during startup.
> 
> I meant to ask this before:
> 
> Which end are you disconnecting the cable at?

Just where the cable goes into the DEC3000. It behaves the same way if I leave the cable connected and switch off the PC.

> If you're disconnecting at the PC/terminal end, then it is about 99.9%
> likely that the cause is simply noise on the line.
> 
> If you're disconnecting at the 3000's end then it's still possible
> there's noise that looks to the UART like a BREAK signal, though it's
> much less likely in that case of course.
> 
> That stack trace you showed looks exactly right for a proper "drop me
> into the debugger" BREAK interrupt on the console.  I.e. it's doing
> exactly what it is supposed to be doing in those circumstances.
> 
> Perhaps theres a dodgy component in the console serial interface.  You
> might be able to fix it by replacing the associated RS232 line
> driver(s) and any discrete components in the same circuit.

Possibly. When I get the time I will try my other DEC3000. The machine with the problem ran OK with 1.6 though I did open the box to replace a drive before installing 2.0.

Perhaps there are two problems here: faulty hardware in the DEC box and a new vulnerable driver for the console device.


> > Does anybody have any suggestions about this problem?
> 
> Don't disconnect a serial console during operation!  :-)

Yes, though where I work we have probably a hundred DS10's running Tru64. If you want to work on a machine you plug a flying console cable into it, shut it down, start it up, check that it is ok and then pull the cable out. Halting at that point would be a bit sub-optimal.

> > Is there anything I can do in the debugger?
> 
> Well you can hopefully type "continue".....  :-)

Yes, that works.

> 
> You might also want to build a kernel with
> 
> 	options DDB_FROMCONSOLE=0
> 
> so that BREAK is ignored by default.

Thanks. I have ordered a CD with the source code (I don't want to hit my employers DSL bill too hard). When it arrives I will try that.

> You could then turn it on with "sysctl -w ddb.fromconsole=1" only
> after you have securely connected the serial port to a powered up
> device.

Thanks again.
-- 
Michael Smith