Re: kern/55774: Kernel panics if another PC is powered on with serial cable attached between two

[Andrius V <vezhlys%gmail.com@localhost>]

Hi,

Yes, it is ddb on break. I didn't know about this functionality and
somehow it took me a while to realize the pattern. Thank you for the
help and information. The bug can be closed.

Regards,
Andrius V

On Mon, Nov 2, 2020 at 7:35 AM Martin Husemann <martin%duskware.de@localhost> wrote:
>
> The following reply was made to PR kern/55774; it has been noted by GNATS.
>
> From: Martin Husemann <martin%duskware.de@localhost>
> To: gnats-bugs%netbsd.org@localhost
> Cc:
> Subject: Re: kern/55774: Kernel panics if another PC is powered on with
>  serial cable attached between two
> Date: Mon, 2 Nov 2020 06:32:13 +0100
>
>  On Mon, Nov 02, 2020 at 12:55:23AM +0100, Joerg Sonnenberger wrote:
>  > That's not a panic, but ddb-on-break?
>
>  Exactly. Easy workaround: set the ddb trigger sequence to something
>  else (popular option: +++++), see cnmagic(9) for a description of
>  the format and then set it via /etc/sysctl.conf like:
>
>  hw.cnmagic=+++++
>
>  Background: many PCs force the TX signal of all on-board com interfaces
>  to 0V for an extended period during power on. This signals a "break"
>  condition to the peer, and the console code reacts to it by invoking
>  the kernel debugger.
>
>  Martin
>