IIfx ROM SIMM in a IIsi . . .

#31 Sat, 8 Oct 2011 - 23:31

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#32 Sat, 8 Oct 2011 - 23:48

IIRC, some of the extra ROM storage includes what we've assumed to be repeated copies of the same ROM.

If so, could some be copies of earlier ROMs with the proper startup sound for, in this case, the IIci? :?:

Is there anything in the Inside Macintosh startup procedure documentation that indicates that a CPU might look for a machine ID indication (bus multiplier type resistor array?) or poll the system for Mac specific ASICs before banging on one particular ROM image's door?

Dunno, just spitballing! :-/

#33 Sun, 9 Oct 2011 - 00:07

Well, the repeated copies of the same ROM don't repeat inside the size of the ROM chips -- they are repetitions of the entire ROM contents. They do that because some of the address pins are left unconnected, depending on how big the installed ROM chips are.

In this case, it means that they definitely left earlier IIci startup code somewhere in the ROM. In fact, they went so far as to leave in the old *synthesized* startup sound code for II series Macs (along with the sampled startup chime that the 650 uses).

http://mess.redump.net/mess:driver_info:mac_technical_notes

The above list seems to show on some II series Macs, a few of the VIA data register bits will identify the model.

#34 Fri, 14 Oct 2011 - 01:43

Interesting question:

IF . . . the IIfx requires SIMMs of 1MB minimum capacity . . .

IF . . . the IIfx RAM banks need to be of equal size . . .

Then . a IIfx needs a minimum of four 1MB Simms installed in both banks to boot . . .

Might a IIsi with 1MB soldered into Bank A, actually boot with 4 256Kb "Keychain" SIMMS in Bank B with a IIfx SIMM installed? :?:

Maybe it's time to rummage around for some Keychain fobs! :

#35 Thu, 27 Oct 2011 - 03:30

The saga continues . . . quotes pulled from the Trading Post:

I can't believe that I can't locate any of these pestiferous POS SIMMs in my MacPartsHorde . . . but I can't!I'd appreciate it it someone would sell me a set of these Paleolithic keychain fobs for a hack project test. :I

TIA,

jt

I have a matched set of 4 if you still need them. Pulled from a Mac Plus, just a few weeks ago, so they definitely work.

What are you building that needs 256k SIMMs?

AichEss has already made the generous offer of mailing a set out for me tomorrow, but thanks! :b&w:
I'm re-testing the IIfx ROM SIMM in a IIsi . . . Hypothesis, in hopes that the minimum requirement of 1MB SIMMS to work in the IIfx, would be that 1MB was the smallest custom SIMM Apple ever made available for that $10,000 beast.

Even in 1990, a 4MB SIMM as the lower limit probably ought to have been the choice of any other Unix capable Machine Mfr for anything they had the stones to declare as "wicked fast!"

The IIsi has 1MB soldered in as Bank A, so before hacking 4MB or more into Bank A . . .

. . . I might as well see if installing 1MB in Bank B will do the trick for equalizing the memory banks! :approve:

If the IIsi boots from the IIfx ROM SIMM in a 2MB config, it'll save me a lot of bother . . .

. . . my original, bought new, Rocket 33 that's slated to go in there already has 32MB on board right now . . .

. . . and it'll only be using the IIsi to copy its ROM into RAM, as an I/O processor, Video Card Cage & networking port.

Forgot to mention, with any luck, as an ATX PSU upgrade enclosure for itself . . .

. . . and two or three PDS Cards slung under the MoBo! }

To finish up the "thread" on a Good, Bad & Ugly note:
The good: thanks ever so much for the 256k SIMMs, AichEss. Safely arrived & tested.

The Bad: I still get the 5(?) note death chime with my stock IIfx ROM and the Hacked ROM SIMM in the IIsi.

The Ugly: gotta start looking into maxing out Banks A & B with a 72 pin SIMM Hack again . . .

@*&/*0\&^*&%&^$%!!!!!!!!!!!!!!!!

Thanks again, aichess! Time to lock that thread . . . [V]

#36 Thu, 27 Oct 2011 - 05:50

Hmmm....this is gonna be tough to figure out. The death chime doesn't necessarily indicate a RAM problem, so something totally different could be causing it too.