The IIfx PDS is a bit odd. Ignoring the pinout issues, there are 3 different ways of using the PDS:
1) You can map your card into normal slot/superslot space and you'll get 10MHz accesses with a clock provided on the PDS slot
2) You can map your card into special address space and you'll get 20Mhz accesses with a clock provided on the PDS slot
3) You can map your card into a different special address space and you'll be accessed at the full 40Mhz, but no 40MHz clock is provided. You need to do your own clock and then synchronize it with one of the provided clocks.
If you're doing a peripheral, you need to map yourself into the normal slot space to get your declrom declared, and provide any necessary drivers, then the special stuff needs to be mapped to different addresses that can be accessed by your driver.
The memory controller is what's doing the special clocking based on address accesses, so you don't get any control over that.
It's all pretty wonky, and seems like it would be fairly difficult to rework any existing peripheral's nubus/pds design into the IIfx's PDS in such a way to actually get any benefit over just using nubus.
1) You can map your card into normal slot/superslot space and you'll get 10MHz accesses with a clock provided on the PDS slot
2) You can map your card into special address space and you'll get 20Mhz accesses with a clock provided on the PDS slot
3) You can map your card into a different special address space and you'll be accessed at the full 40Mhz, but no 40MHz clock is provided. You need to do your own clock and then synchronize it with one of the provided clocks.
If you're doing a peripheral, you need to map yourself into the normal slot space to get your declrom declared, and provide any necessary drivers, then the special stuff needs to be mapped to different addresses that can be accessed by your driver.
The memory controller is what's doing the special clocking based on address accesses, so you don't get any control over that.
It's all pretty wonky, and seems like it would be fairly difficult to rework any existing peripheral's nubus/pds design into the IIfx's PDS in such a way to actually get any benefit over just using nubus.