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From: Hans Petter Selasky <hselasky@c2i.net>
To: Alexander Best <alexbestms@math.uni-muenster.de>
Date: Mon, 3 Aug 2009 21:27:30 +0200
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Cc: freebsd-usb@freebsd.org
Subject: Re: kernel debugger and usb keyboard
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On Monday 03 August 2009 20:55:16 Alexander Best wrote:
> just tried settings `sysctl debug.kdb.panic = 1`. if i use this way to
> enter the kernel debugger my usb keyboard works. if i type "continue"
> however the kernel panics and the kernel debugger gets yet entered again,
> but without the keyboard working.

The USB controller which the keyboard is hooked onto will not work after panic 
has been entered, due to some state not being cleaned up.

To increase the chance of the keyboard working on a panic, connect the 
keyboard to a separate USB controller. 

> i don't know how to produce backtraces since the keyboard doesn't work.

Ok.

>
> the other way of entering the debugger without my keyboard working was to
> simple press "ctrl+ast+esc".

Yes, because most likely the DDB is entered directly from the USB keyboard 
code, and the USB stack does not allow function recursion in that case!

--HPS