The Great Mystery of the IIfx PDS

[Mk.558]

Some, too, have baffled his analytical skill, and would be, as narratives, beginnings without an ending, while others have been but partially cleared up, and have their explanations founded rather upon conjecture and surmise than on that absolute logical proof which was so dear to him. There is, however, one of these last which was so remarkable in its details and so startling in its results that I am tempted to give some account of it in spite of the fact that there are points in connection with it which never have been, and probably never will be, entirely cleared up.

Adventures of Sherlock Holmes, the Five Orange Pips short
These words came into my mind while I contemplated the strange Macintosh IIfx PDS bus.

I have yet to hear of an accelerator for this unit which is compatible with it and uses the PDS slot. In fact, the only thing I have found is this: http://www.flickr.com/photos/7757990@N08/470092935/

Has anybody else found any PDS cards for the IIfx, of any kind in the wild? It seems to me that most hardware developers would not even bother, since the unit was so expensive, versus developing NuBUS cards instead.

 

[bbraun]

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.

 

[Unknown_K]

Bus Mastering doesn't work on the IIfx PDS as told by me from the Designer of the Tokamac IIfx PDS card.

"Yes, the motherboard did require that we replace a PAL to enable functionality that Apple claimed worked but never actually tested (that the PDS slot could become a bus master)."

 

[Mk.558]

Anybody else know of any exotic cards for the IIfx?

I looked through Trash80's scans concerning accelerators and it happens that all the compatible "accelerators" for the IIfx were total reworks, not some Daystar or similar drop-in card.

 

[Unknown_K]

Here is the Tokamac drop in 68040/33 for the IIfx.

https://picasaweb.google.com/107784270771159898725/NubusCards?gsessionid=uaOAuxiVBWsKmd6JtCTSPw#5067908774971265362

There is also the Applied Engineering TransWarp 25/33 68040.