Uninstalling Firmware

With the given script it is possible to reflash the same (or even an older) version of a plain Apple firmware and thereby remove any patches by third-party vendors.

It is important that this must only be done on a system without a CPU upgrade (using the 7447 and 7448) that requires firmware patches. The Mac would be dead until the reinstallation of an original G4 or other type of accelerator !

NVRAMRC patches for booting into Mac OS 9 will survive a flash, but can get cleared using Command-Option-P-R. Other similar patches (as the lba-48 property) would have to be reapplied.

Retro-fitting old FirmWare and re-installing the newer

Searching through my CD archive I've found two different versions of the firmware updaters for the PowerMac G4 and the Cube (as well as the iMac, iBook, PowerBook and even a G3) on Mac OS install CDs:

Mac OS	PowerMac	Cube
9.2.1	4.1.8	4.1.8
10.1	4.1.8	4.1.8
10.2	4.2.8	4.1.9
	(both are still current)

Using them I successfully downgraded the firmware of a Sawtooth from the current 4.2.8 to the older 4.1.8 and back to 4.2.8 again. Further analysis of the code shows that it will only flash a firmware with the same major version as in the ROM (or upgrade from 3 to 4 as a special case). Even the firmware from another model would be accepted — Never ever try such a crossflash as it will most likely leave the motherboard completely dead and therefore without a possibility to correct the flash !

The firmware NVRAM variables will survive the flash, including any NVRAMRC patches (as the lba-48 property), but do NOT flash a plain firmware with a (7447 or 7448 based) CPU upgrade that requires its own patches.

While at it I also tested manually booting the flasher from the Open Firmware command prompt. With one of the CDs from the table above (or a CD-R with just the "Firmware" file) it is possible to upgrade or reflash the firmware without any Mac OS on the system !

No Macintosh was harmed during the making of this post.

Running Firmware Updaters from Mac OS X

Judging from my analysis of the Firmware Updaters for various G4 (including the cube) it should be surprisingly easy to run those flashers officially "requiring" Mac OS 9 from OS X instead !

The "Firmware Updater" included in such a download does NOT perform the flashing, but only checks if the update can be applied ("Firmware" file supports the Mac model and has a newer version) and arranges to restart the Mac into the "Firmware" file. This file not only contains the new firmware image, but in front of it also the complete program required to flash the ROM. The flasher is written (mostly) in FCode source allowing deep insights into its inner workings (if Forth is your kind of bedtime reading).
All of this means that the flasher runs in the context of the Open Firmware before any part of (any) Mac OS is even loaded and does NOT depend on a specific version. It should therefore be possible to simply boot a copy of the "Firmware" file on a hard disk from the Open Firmware command prompt.

In order to make this process painless to comply with I've created a short script (available for download as fwupdater):

#! /bin/bash -

flasher='/Volumes/G4 Cube Firmware Update/G4 Cube Firmware'

cp -ip "$flasher" /TrashMe || exit

 preferred=(`nvram boot-device`)
IFS=\",  bootpath=(`ioreg -p IODeviceTree -n chosen -w0 | fgrep bootpath`)

sudo nvram boot-command=mac-boot boot-device="${bootpath[3]},\\TrashMe" \
 preferred-boot-device="${preferred[1]}" &&
osascript -e 'tell application "System Events" to shut down'
sudo -k

It first copies the "Firmware" file to the root of the boot disk and carefully sets it up as boot-device so the flasher will run on the next system start, even it is on a slave ATA disk or maybe an external firewire drive. The flasher will restore the former boot-device after it's done. No verification is performed, but the flasher will roughly test for compatibility on its own.

Steps to follow while logged in as an administrator:

1. Download the updater. English is assumed, but the firmware itself is not language dependent.
2. Print the instructions while still on this page.
3. Open the disk image so it will appear on the desktop.
4. Open fwupdater from the Finder. It will launch in a Terminal window and ask for your password so the boot device can be set. After that the Mac will be shut down.
5. Closely obey the printed instruction on turning on again while holding the programmer's button (beginning with step 4).
6. The flasher will restart the Mac after the update. Use the System Profiler to verify the new Boot ROM Version.
7. Delete "TrashMe" from the root of the boot disk.

The script can be used for other PowerMacs with Mac OS 9-based firmware updaters, if the pathname at the top is set to the correct "Firmware" file.

IMPORTANT: I don't have a PowerMac requiring an update anywhere near me, so my tests couldn't include the flashing itself, and were only performed under Leopard. I'm confident that the method described here does work (under any version of Mac OS X), and it eliminates the need to "borrow" (or buy) and install Mac OS 9 when a firmware update is all that is needed.
Volunteers ?

Myths that won't die …

Mac OS X virtualizes video RAM and will NOT partition it between two monitors, even if some older tools claim otherwise. Video RAM gets assigned to whatever needs it, so with two monitors connected an application can still use nearly all of your 256 MiB (minus the frame buffer for the second monitor, a few window images from Quartz Extreme, etc). Core Image and Quartz GL should be able to make good use of all the free VRAM.

MacOS 9 did split the VRAM between two active monitors. These different behaviors can be seen with "ATI Displays" on Radeon cards under both systems.