J12 looks like the mezzanine connector

Ssp3 try it the new studio m5 ultra is awsome for AI

In addition to the card itself, a Mac Mini needs an additional board connecting it to the motherboard. This is called a "mezzanine board." There are two versions of the mezzanine board – one (older) compatible with the A1027 card (found in "early" Minis) and the other compatible with the A1127 card (used in 1.33 and 1.5 GHz models). I'm not sure if they're compatible/interchangeable (Powerbookmedic says they are). Of course, if you have an A1127, it's a "combo" (WiFi and Bluetooth), while the Bluetooth module is separate in the case of the A1027. Additionally, you'll need antennas (note that the antenna connector for AirPort is different between the A1027 and the A1127).

https://www.ppa.pl/forum/morphos/38908/mac-mini-g4

https://www.macdat.net/files/pdf/apple/servicesource/mac_mini.pdf

J12 mezzanine connector: 80 pins
Standard 32-bit PCI: 124 contact positions
PCI positions excluding power and ground: approximately 78

This makes an 80-pin connector theoretically interesting for a custom PCI interposer.

who wants to identify which PCI signals----if any---are actually routed to J12 on the Mac mini G4 motherboard

@smilesdavis, have you, by any chance, been talking to AI lately?  Those graphs look very familiar.. 

@smilesdavis wishing you the best of luck.

@IIO: PCI is limited to the number of devices, before you need a bridge.  If a new bridge is needed, the firmware may or may not scan it.  (So this slot may only support a single device, etc).

For something like a video card that was needed at boot time this would be unfortunate.

But for arbitrary devices that can have their drivers loaded when needed it is no problem at all...provided the firmware sets the device tree up properly...or the driver can scan if it doesn't.

This sounds plausible and possible, and something I have wondered about also.

The trick will be if the firmware will query roms on the PCI bus that the airport card uses.  If it does, you're gold.  If it doesn't some work will be needed. 

On the other hand, if you don't need cards on the new PCI bus at boot time, the drivers can just be loaded as needed.

well in times of UnexpectedBomb i think that shall be the least of our problems

The magma 4slot would then be a selfcontained mac os 9 mix cube system with usb2.0

i will scan the 1.25ghz mac minimezzanine

PowerBook6,5 256MB with Radeon 9200

I also tested the 14" Powerbook6,5 with 512MB RAM and it works too.

 I'm not sure if these macs originally came with the A1026 card: both of mine were pretty badly stripped down, "for-parts" laptops that had clearly been messed with quite a bit before I got them.  I pulled one of my A1026 Airport Extreme cards out of an Airport "Base Station". (Why can't Apple call things by normal names like "router" and wifi card?) The A1026 card in the 12" ibook I found laying around in a drawer. I forgot what mac it came from....

Excellent. This is very helpful information! And I know what you mean... Apple can't sully their reputation by using the same vernacular as the unwashed masses 

@lauland: what is the main difference between the PCI card expansion slots and all other PCI buses on a desktop G4 mobo (or possibly any other personal computer?)

This sounds plausible and possible, and something I have wondered about also.

The trick will be if the firmware will query roms on the PCI bus that the airport card uses.  If it does, you're gold.  If it doesn't some work will be needed. 

On the other hand, if you don't need cards on the new PCI bus at boot time, the drivers can just be loaded as needed.

Apple officially sold the G4 mini as having “no PCI slots,” yet internally it has a 33 MHz PCI host and Apple routed that PCI bus right to a removable expansion module.

https://leopard-adc.pepas.com/documentation/Hardware/Developer_Notes/Macintosh_CPUs-G4/MacMiniG4/2Architecture/q88_archi.html

- the mini already contains a real conventional PCI bus
- The Intrepid I/O controller has a 32-bit PCI bus with a bus clock speed of 33 MHz.
- The connector for the AirPort Extreme Card uses the PCI bus.
- The mini's host bus is exactly the sort of bus your older Digi cards expect: 32-bit PCI at 33 MHz.
- Apple also used the same generation AirPort Extreme card across many G4/G5 Macs. Available Apple schematic material for that interface shows essentially the conventional PCI ingredients: AD address/data lines, C/BE, FRAME, IRDY, TRDY, DEVSEL, STOP, clock, reset, interrupt, REQ/GNT, IDSEL, etc. (https://www.informaticanapoli.it/download/SCHEMIELETTRICI/APPLE/Q45-G5-IMG5-051-6482-080304-RC.pdf)
-


Mac mini G4
    │
AirPort PCI
    │
custom PCBway interposer* for CardBus
  │
Magma Chassis
    │
 ┌─┼───────────────┐
PCI cards.....

a theoretical adapter should have its own regulated PCI power supply

Mac mini AirPort
  PCI SIGNALS ──────────────────┐
  GND ──────────────────────────┤
                               ▼
                         PCI connector
                               ▲
external PSU:
 +3.3 V ────────────────────────┤
 +5 V ──────────────────────────┤
 +12 V ─────────────────────────┤
 -12 V if required ─────────────┘

Grounds obviously have to be common.

G4 minis don't put the AirPort card directly onto the main logic board. They have a removable mezzanine board (820-1660-06) which can simply be removed from the motherboard, and replacement boards exist as Apple parts 922-6671 / 922-6893. The late 2005 1.33/1.5 GHz revision is less attractive, because Apple revised the mezzanine and integrated the wireless hardware more tightly. Earlier 1.25/1.42-era hardware gives us the nicest physical starting point.

That means I would not touch the Mac mini motherboard initially.

Mac mini motherboard
       │
 original mezzanine connector
       │
 donor mezzanine PCB
       │
 [remove AirPort connector /
  attach interposer here]
       │
 normal PCI

┌────────────────────┐
│    Mac mini G4     │
│                    │
│ Intrepid PCI       │
│      │             │
│ AirPort connector  │
└──────┼─────────────┘
       │
       │ custom PCB
       ▼
┌────────────────────┐
│  32-bit PCI slot   │
│  external power    │
└──────┬─────────────┘
       │
    Magma
   host card
       │
       ║
       ║ Magma cable
       ║
┌──────▼─────────────┐
│ MAGMA 4-slot PCI   │
│                    │
│ MIX Core           │
│ MIX Farm           │
│ DSP Farm II        │
└────────────────────┘

Awesome! That's a dream come true!
Thank you!!!
Can't wait for the DBT-120 to work with OS9!

Nice, good luck! Looking forward to seeing your developments, what you've done already is fantastic.
It was wishful thinking on my part I think it's more of a problem/combination of PSU pinout/GPU/ADC now that I think back to it. I've got a combination that works, but it's tricky when you don't have access to the right hardware pieces.