From: Bruce Johnson <[EMAIL PROTECTED]> Subject: Re: [PCI] 8600/300 mobo. Date: Fri, 21 Jan 2005 15:10:20 -0700
On Jan 21, 2005, at 2:25 PM, Blake Hanes wrote:
ok since i dont own one of these what would happen if you put in a rom simm into that slot just curious
None were ever made. I don't know if the ROM from a beige will fit into that slot; but almost certainly you would have a non-bootable system if you did.
I made a study of this chasing the lower slot issue in the S900 (which is a firmware (ROM) bug).
The ROM modules for the x100 through the Beige G3 have the same pinout and form factor. That's right, this ROM *hardware* design goes all the way back to the NuBus PowerMacs.
However, the contents of the ROM are wildly different. Bruce is correct that the ROM from a Beige will not boot an 8600 or any other machine in the x500, x600 family.
There are two reasons for this. First, the Beige G3 ROM uses a 3.3V supply and the 8600 et. al. use a 5V supply in the ROM. The 5V and 3.3V supplies are on different pins on the ROM, but I don't think that the socket in the 8600 supplies 3.3V to the appropriate pins--those pins are just unconnected in the 8600. This is the hardware issue.
Second, the Beige G3 code is wildly different from the x500, x600 family code. For example, the Beige G3 has at its heart the Motorola MPC106 memory controller/bus arbiter/PCI controller (Grackle), whereas the x500/x600 family uses a Hammerhead memory controller/bus arbiter and a separate Bandit PCI controller and the ROM code (firmware) must reflect these differences.
However, undaunted by the obvious hardware differences, I built a ROM DIMM on which I installed 5V memory chips and to which I wrote the Beige G3 ROM code. I can confidently report that there's no sign of life in an x500/x600 machine when this bastard ROM is installed.
Aha, you say, how do you know that your ROM DIMM was any good? Simple, I used Intel 28F800 Smart Voltage chips which can run at either 5V or 3.3V. Then I moved the power supply connections to the 3.3V pins and it works fine in a Beige G3. I suppose it is possible that the Beige G3 reads its ROM in the opposite byte order as the x500/x600 though.
Additionally, I built other ROMs using the 8600/9600 ROM code and installed those in earlier x500 machine. They worked fine. So I know I can build an x500/x600 ROM which works. It just doesn't work when the Beige G3 code is on the chips.
All that said, there'd never be any reason to install a ROM in the 8600/300 unless you were a super firmware hacker. The 8600/300 already has the latest ROMs ($77D.34F5). There is no later improved ROM code for that machine--unless you write it yourself.
However, there is a small benefit in installing the 8600/300 ROM code ($77D.34F5) into earlier x500 and x600 machines. The $77D.34F5 code solves an incompatibility with G3 processors and speculative processing. If you put the $77D.34F5 ROM in one of those earlier machines you can enable speculative processing on your earlier machine for an imperceptible boost in performance.
Jeff Walther
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