Subject: Re: 2.0 on DEC3000 drops to debugger if console is not connected (resend)
To: Michael Smith <email@example.com>
From: Greg A. Woods <firstname.lastname@example.org>
Date: 01/04/2005 18:15:59
[ 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?
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.
> Does anybody have any suggestions about this problem?
Don't disconnect a serial console during operation! :-)
> Is there anything I can do in the debugger?
Well you can hopefully type "continue"..... :-)
You might also want to build a kernel with
so that BREAK is ignored by default.
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.
Greg A. Woods
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