So on a p7 you’d have firmware running big endian, a big endian Linux running in hypervisor mode, and then could have little endian guests. We kept the skiboot (i.e. runtime firmware) support for POWER7 around for a while, and according to https://github.com/open-power/skiboot/blob/326a4666bd69ca071c4f7d2eacf868b11099baee/doc/platforms-and-cpus.rst#dropped-platforms it was removed during the 6.3.x cycle, so https://github.com/open-power/skiboot/tree/skiboot-6.2.x would be the last one that run on p7. There was never a public release of the POWER7 firmware that included support for running Linux as a hypervisor, but it’s probably not too hard to work out what you need to do if you’re somewhat determined.

The POWER8 systems were the first to ship with OPAL firmware as an option, and then the OpenPOWER machines only ran it. The POWER8 fixed the missing HILE bit – Hypervisor Interrupt Little Endian – as the issue with the P7 was that you’d end up taking a hypervisor interrupt and it’d always be in Big Endian mode…. a *challenge* for a little endian OS to deal with.

With P8 there was also the addition of the switch_endian() system call, and this is used by opal_prd – which is a userspace program that runs some (big endian) code from firmware. It stands for OpenPower Abstraction Layer Processor Runtime Diagnostics. Running this firmware in userspace allowed it to be scheduled, get logs out to the OS nicely, and if there were bugs in it, you’d just get a core dump rather than crashing weirdly somewhere in firmware.

The firmware also remained Big Endian. So you could have a Big Endian firmware, being called by a Little Endian hypervisor OS, running a Big Endian guest, or this big endian code in a userspace process. It made for.. umm… “interesting” backtraces where you had to remember what endian mode everything was in. Typically this was looked at either with attaching special hardware, or just with https://github.com/open-power/pdbg from the BMC.

Part of the reason I made this post was to document one of these machines so that when someone decides to write an emulator for this (or the 7248) or wants to fix theirs they can. Most photos of this machine are blurry, low-res photos taken in the early 2000s with early digital cameras, and hardware info usually revolves around making old versions of Linux boot on it.

I know another 7020-40p owner and his machine either had a PSU issue or “just quit working” after a HDD upgrade. I don’t know many other 40p/440 owners, the most common PReP machine from what I’ve seen is the 7248 while PPC Thinkpads are collector items these days. There was a $2,500 PPC Thinkpad eBay listing recently and while an offer was likely made it did in fact sell. 7248s pop up for considerably less on eBay from time to time.

While I’m at it, here’s screenshots from the ARC menu of the PCI devices:
https://imgur.com/a/wWOBWLm

I recently had a lot of fun trying to get NT 4.0 to work on a Motorola PowerStack II board, that had OpenFirmware on it… I finally was successful by installing Motorola’s original firmware. I would love to try out 3.51, but I guess there is no HAL for the PowerStack II…