How does a Mac know which one it is?

[nyef]

On a quick read it looks like an SE/30 might be hoodwinked into thinking it's a IIcx, the design upon which it was based. That would be most fortuitous.

If the VIAs are surface-mount, it might be as simple as lifting a pin and tying it to the 5v supply. If they're socketed DIP, pull it, bend the pin out, put it back in, and solder a bodge wire to 5v. If they're soldered-in DIP, cut the pin and solder a wire to 5v. Or, in all cases, if the pin goes to a trace, cut the trace, then solder the to 5v.

Unless the pin is negative-logic, in which case tie it to ground.  In all cases, it's a fairly reversible patch, though it may be obvious after the fact that you've done something even if you reverse it.  Fairly easy thing to test, provided that pulling the mainboard is easy (and, while it's been a long time since I've had an SE/30, I seem to recall that it is easy).

 

[Trash80toHP_Mini]

If the VIAs are surface-mount, it might be as simple as lifting a pin and tying it to the 5v supply. If they're socketed DIP, pull it, bend the pin out, put it back in, and solder a bodge wire to 5v. If they're soldered-in DIP, cut the pin and solder a wire to 5v. Or, in all cases, if the pin goes to a trace, cut the trace, then solder the to 5v.

Thanks, it's back to the schematics to see if I can noodle out which traces might head to the VIA's pins from what resistors on the board. Swapping a resistor on its pads might be the way to go if possible. Gotta check to see where values  differ between the two models using the same ASIC.

At least I've got a starting point now! [] ]'>

 

[Trash80toHP_Mini]

Found some interesting info from the gamba pages hosted by BMOW on upgrading the SE/30 to unsupported OS levels with a Clean ROM installed.

Mac IIx and IIcx Note: It was originally believed these patches were only necessary for the Mac SE/30, but we’ve since learned they’re also relevant to the Mac IIx and IIcx, and possibly others too. Gamba’s instructions below will direct you to find sections of the System file with this general form:

… 0007 0003 0008 0003 0009 0003 …

These are pairs of gestalt IDs followed by boot methods. The boot method is 0003 for each of the gestalt IDs 0007, 0008, and 0009. For System 7.5 or later to function correctly with an alternate ROM, you must find the gestalt ID for your Macintosh model, and change the corresponding boot method to 0005. The notes below are specific to the Mac SE/30, which has gestalt ID 0009. The other relevant IDs are:

0007 – Mac IIx
0008 – Mac IIcx
0009 – Mac SE/30

< snip >

1. After Installer is done, restart with 7.0.1 Disk Tools floppy and do:
   
    ResEdit hack to ‘System 7.5 Update’ file in ‘System Folder’:
   
    • ‘gusd’ resource ‘ID 1’ at offset ‘000018’, replace data ‘0008 0003 0009 0003‘ with data ‘0008 0003 0009 0005‘.
   
    ResEdit hack to ‘System’ file in ‘System Folder’:
   
    • ‘gusd’ resource ‘ID 1’ at offset ‘000018’, replace data ‘0008 0003 0009 0003‘ with data ‘0008 0003 0009 0005‘.
2. Use System Picker to select hard drive OS 7.5.3 for reboot.
   

So the Gestalt ID choices are coded in ROM along with the boot methods required for each and gamba info details how to hack the gusd resource for SE/30 shenanigans.

The question now would appear to be where the heck to hack the SE/30 to return the Gestalt ID of the IIci. IIcx or IIx?

IIcx would seem the obvious choice to me, as it's purportedly the basis for the SE/30. ISTR reading that the SE/30 was actually based on the IIx, which makes more sense to me. Both IIcx and SE/30 would have been in development at almost same time, more likely making them siblings out of the same IIx dam.

Telling the PowerCache in the SE/30 that it's in a IIx might just allow it to more flexibly support bus mastering as it does on that and other Macs than seems to be possible than it might under an SE/30 Gestalt ID

Standard SE/30 with its native 68030 processor running under its own Gestalt ID from its standard, 24bit dirty ROM toolbox routines is problematic. The stock SE/30 does a piss poor job of supporting bus master cards (some IIsi cards, most notably the NuBus adapter) awhich is explained in DCaDftMF as the reason its incompatibility with those IIsi cards.

I'm hoping the PowerCache, having taken over the SE/30 at the PDS level, might possibly do bus mastering on that bus however it decides to, including support for a NuBus chipset.

I hope this makes some little tiny  bit of sense to somebody  .  .  .  anybody?