I haven't updated this page in a while as I no longer have a machine that I can do hacking on. Most of my programming time has been spent in user-space. :-) Please note that this information is not relevant for Intel-based PS/2's. The knowledge you seek resides at I'm going to leave the info here for the forseeable future, however. I do have an interesting email from one intrepid reader, however. The contents are included here:

Date: Wed, 25 Jul 2001 07:08:36 -0600
From: "Charrier, Michael S" <despammed>
To: "''" <>
Subject: AIX, RS/6000s, and MCA

Thought you might want to post this on your Linux/rs6k web site:
I was in a meeting with a group from IBM a few days ago.  During the meeting
we were told that IBM will be DROPPING SUPPORT for the Microchannel RS/6000
systems in AIX!  The currently available versions of AIX (4.3.3 and 5L v5.1)
support RS/6000s with MCA, but support for MCA will be dropped from AIX in
5L v5.2.  This will happen in about 12 months.

It now becomes a little more urgent that Linux be ported to the MCA RS/6000
boxes; when IBM stops selling 4.3.3 and 5L v5.1 no one buying a MCA-based
RS/6000 will be able to get an OS to install on the system.

Mike Charrier

So far, we have made a boot disk that you can use to write a number to the three digit display on the front of your machine. Don't laugh, it's harder than you think :-). Andrew did this to determine how we can get our stuff loaded into memory.

To use it, poke around in the messages and put the img file you will locate on a floppy disk, flip the key on the front of your machine to service, and turn on the machine with the floppy in the drive. If it doesn't work, make sure your bootlist on the machine is set to boot from floppy at some point in the service mode IPL.

There isn't anything here that you can install on your machine, we don't really even have patches yet. If you have any info on the architecture, please post a message or mail me (David). If you would like to remain anonymous, let me know. If any IBM employees can arrange for a (NDA'd) peek at the AIX bootloader, that would make my day.

The data we currently need the most includes:

Update of above
I received an email from David Edelsohn clarifying some of the above points. Below are the contents:

        The very first thing that AIX does after it has been relocated
from the initial boot image loaded at address 0 is:

        cal     r2,MSR_ME|MSR_AL(0)     # set msr = disabled, xlate off
                                        #   (machine check and alignment
                                        #    enabled only)
        mtmsr   r2

So it really does not matter how the MMU is configured, turn it off in the
MSR.  I presume that it is disabled because the boot code walks through
all of the kernel image shifting the kernel down so that its base is at
address zero instead of the image header.

        I cannot tell where the IPL CB is actually located.  The AIX
kernel does not seem to care and its loads the entire image without
worrying about trampling the IPL CB.

        ROS apparently does very little initialization, but I cannot tell
how much MCA initialization is done other than locating all of the BUCs.
Everything is accessed through the POWER T=0(?) special addresses.

There are a few interesting messages from the linuxppc-dev list that will be helpful to anyone planning on coding.

Some stuff from Motorola