That maybe a better solution, I don't know the speed of that cache slot on the 6500, or how many PCI slots it has. The limitation of the Sonnet 7200 card was the 33Mhz max PCI that never really got near 133MB/s anyways.
Then you would have whatever space limitations of the PCI slot area in the 6500.
PCI does gave a little more versatility in what you can do with the slot and there maybe no way to stack memory and whatever controller maybe needed for that into the L2 Cache slot of a 6500 board, whereas PCI can be expanded and bridge chips can be put on cards.
It's not like the old days of exorbitant priced PCI expansion cases. A PCI to PCI-E raiser, and PCI-E to PCI boarder are less than $100 with cabling that may allow internal space of the 6500 that is unused to be utilized.
The benefit the of 7200 solution is it's already made, it would just require the proper drivers, the draw back is these cards are almost none existent in the 'I want to buy it now' space.
We'd really need to clone it, which should not be an issue given patens should have expired.
It would be nice if former Sonnet engineers were about where we could pick their brains, but NDA's last longer than patens.
A more elegant solution, and a more realistic one, is upgrading the 6500 with an Arm64 based logic board.
Emulation of PPC has come a long way, my M2 MacBook runs the Mac OS/X PPC versions just fine, and I have even used PCI Passthrough for PCI/PCI-X cards in QemuPPC.
As of this time, Raspberry Pi dominates the consumer build you own system in Arm, and lacks PCI/PCI-E or Thunderbolt for the type of expansion we may require to utilize our old PCI devices used by the applications we run to keep us on the PPC Mac OS, because it still has drivers for our PCI stuff, or the stuff we want to get.
Beging in love with the originality of a logic board that was obsolete over two decades ago doesn't make a whole lot of sense. Even with a custom CPU/RAM upgrade for the L2 slot that is going to cost way more to bring to manufacture than an Arm64 based board that can just replace the entire logic board and not be limited by a 30 year old bus architecture that's bus speed and ram are never going to come close to what Qemu-system-ppc can offer right now.
Openbios still has some limits, but all we really need is some patches for video card FCode ROM words and any HD controllers we may want to use.
They are the only things I can think of that require to be part of the boot process, everything else just works( mostly ) with PCI Passthough and Openbios enumerates it just fine, when the Mac OS boots, the drivers find the PCI devices just as they do in a real Mac, the drivers load and you use you PCI device. With a PCI or PCI-E bus not limited by the 6500's poor PCI Bus performance.
If Apple made a correct form factor logic board for our aging PCI Mac's, we'd be all over it if it could run our needed Mac OS in a mostly seamless way and allowed us to connect with our aging devices in the way we expect, but Apple is not going to do that.
It would mean maintaining support for Mac OS versions they can't secure and don't make any money off of anymore.
Mac OS 9 and older are fundamentally insecure, sandboxing them into a VM is the best you are going to hope for, and emulators are the future of PPC.
My iPhone 10 could emulate Mac OS 9 faster than any Mac that could ever run it when you take into account RAM speed and disk speed.
Some work still needs to be done CPU wise, but mostly that will solve itself with better software optimized to bring better AltiVec performance and FPU.
But Arm is going to keep getting faster without any optimized code, and PPC that will run these versions of the Mac OS never are, not ever.
Sure if you want to run OS 9 or older you'll be limited to PCI graphics, I ran the Rage 128 PCI just fine in Qemu, the real card, not emulation, and played 3d games and had 2d graphics acceleration same as any Rage 128 PCI running in a real PPC Mac, but I did not have the bus and ram limitations.
