ddb_vgapost not working?

[Thomas Klausner <wiz%NetBSD.org@localhost>]

Hi!

I have
ddb.commandonenter=call ddb_vgapost;bt

in my /etc/sysctl.conf, but for the past few weeks (months?) when the
machine hung while X was running, I only got a black screen and a
cursor.

That's with
radeondrm0 at vga0: ATI Radeon HD 4650
radeondrm0: Initialized radeon 1.29.0 20080613
in case it matters.

I remember that it worked at some point, but I didn't notice when
exactly it stopped working.
 Thomas