Remote Firewire dcons use shows my G5 "hang-up point" reports have been wrong: shows lines not shown on the problem context's display

[Mark Millard]

I got remote FireWire dcons use going (partially),

https://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/kerneldebug-dcons.html

# more /mnt/boot/loader.conf
hw.firewire.phydma_enable=1
hw.firewire.dcons_crom.force_console=1
#dcons_gdb=1
#boot_multicons="YES"

[Trying to turn on boot_multi_cons gets stuck at
db> prompts *very* early and the display on the
target ends up with mixed material from two
streams of output. So: no use of dcons for
low level console activity.]

The above combination does show output on the
remote, observing PowerMac, during part
of the boot sequence. And . . .

It shows more lines of output just before the
overall hang-up than the target machine's
display does.

It appears that for most or all the hang-ups
that I've reported, my report indicated a
point earlier then the actual hang-up: more
of the messages were actually generated and
the code got farther than I knew.

So there might be a separate issue of the
screen display stopping its updates before
the old PowerMac G5 has actually hung-up
(overall). Or it my just be timing
relationships do not get a chance to allow
the "next screen update" or some such.

It appears that tracking down hang-up points
via print messages shown on the normal display
can not generally be done on the G5s. FireWire
dcons use may be required (unless there is some
alternative).

I'll note that I was not able to break into ddb
via the dcons connection. It appeared that I
had no ability to input to the target if I had
no such on the directly-connected usb keyboard
at the same time. In other words: I gained no
control but got better observational data.


FYI:

I used (replacing ??'s with appropriate
hexadecimal digits):

dconschat -e \# -br -TC 5555 -t ??-??-??-??-??-??-??-?? &
telnet localhost 5555

on the observing PowerMac. (I happened to use a
G4 as the observer of the target G5.)




===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)