Hackintosh

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If there are PCI-to-PCI bridges between the slots or on the adapter itself, there might be issues with resources not being properly assigned to the card by either BIOS or OS.
There are 2 main ways that a card is found. On a conventional PCI card there are 2 presence lines that can indicate a card is there and give some other information about the card.

Every PCI-PCI bridge has a primary bus interface number, and a secondary bus interface number. The primary bus interface being the one nearest the CPU and the secondary bus interface being the one furthest away. Each PCI-PCI Bridge also has a subordinate bus number and this is the maximum bus number of all the PCI busses that are bridged beyond the secondary bus interface. Or to put it another way, the subordinate bus number is the highest numbered PCI bus downstream of the PCI-PCI bridge. When the PCI-PCI bridge sees a Type 1 PCI configuration cycle it does one of the following things:

- Ignore it if the bus number specified is not in between the bridge's secondary bus number and subordinate bus number (inclusive),
- Convert it to a Type 0 configuration command if the bus number specified matches the secondary bus number of the bridge,
- Pass it onto the secondary bus interface unchanged if the bus number specified is greater than the secondary bus number and less than or equal to the subordinate bus number.

Not all formats of PCI have this capability and some Bios's don't use them either even if there.

The other way is straightforward try the slot approach where a cycle is attempted to see if there is a response.

It is up to each individual operating system to allocate bus numbers during PCI configuration but whatever the numbering scheme used the following statement must be true for all of the PCI-PCI bridges in the system:

``All PCI buses located behind a PCI-PCI bridge must reside between the secondary bus number and the subordinate bus number (inclusive).''

If this rule is broken then the PCI-PCI Bridges will not pass and translate Type 1 PCI configuration cycles correctly and the system will fail to find and initialise the PCI devices in the system.