> Try command-option-escape on your G4 tower.

OK, that works.  (I already saw your corrected message that
mentions control.)  It even works when I log in from /dev/ttyE0.
I can't type anything though.

Can you type at ddb?  What version of OpenFirmware do you have?
ADB or USB keyboard?  And what is the revision number at the top
of your /sys/arch/macppc/macppc/machdep.c file?  I'm wondering
if the machine-dependent keyboard code is to blame (I've already been
glaring at it for quite some time).

> Also, if your console is not secure, I really don't
> recommend running DDB on it.

That's a very good piece of advice, but you still missed my point.
It has to do with a quirk of /etc/ttys.

If I log in on /dev/ttyE0, I can have all four combinations of
"is the root password required when booting in single-user mode?"
and "can root log in at all on this TTY?", by making appropriate
settings in /etc/ttys for /dev/ttyE0 and /dev/console:

root login?	password -s?		/dev/ttyE0	/dev/console

no		no			on		off secure
no		yes			on		off
yes		no			on secure	off secure
yes		yes			on secure	off

If I log in on /dev/console, I can only have two of the four
combinations, which I find unacceptable:

root login?	password -s?		/dev/console	/dev/ttyE0

no		yes			on		off secure
no		yes			on		off
yes		no			on secure	off secure
yes		no			on secure	off

That's because a "secure" entry for /dev/console is treated
differently from a "secure" entry for other TTYs.

Just to be complete, I turned /dev/console and /dev/ttyE0 on at the
same time.  It was a bad idea (the terminal state keeps changing semi-
randomly and "Login:" and "password:" prompts keep popping up).
Not wishing to shoot myself in the foot, I did not try turning both
_off_ at the same time.

I still think the interrupt switch is a sensible alternative; then you
don't have to worry about keystrokes at all (at least not to activate
DDB).

-- Derek