PDS Pi

[VMSZealot]

For no good reason at all other than "because it's there", I was pondering the AST Mac 86 PDS card for the Mac SE, and it got me wondering whether it would be feasible to implement on a Raspberry Pi card, slotted into the PDS card of a Mac SE. Presumably, once a PDS to Pi had been developed, many other amazing things could be made to work through this functionality. Video boards. Accelerators. You name it.

Then I pondered if the same thing could be made to work for NuBus. A 386 or Pentium compatibility card, provided by a Pi, in the slot of a Mac II. A Radius Rocket more rockety than any rocket before.

I don't have the skill for this. It's just a pondering. But for people cleverer than me (just about everyone here), how feasible would this be?

 

[Melkhior]

That's the idea behind the PiStorm and similar. The main issue is that without reconfigurable hardware, the bus must be bit-banged, and at the speed of a 68000 it's not trivial, and for faster things it becomes extremely difficult. Unlike some bit-banged protocols that can live with the occasional error, the system bus of a CPU is unforgiving and won't tolerate any slip-up.
With reconfigurable hardware (CPLD, FPGA, ...) it's much easier as they can be synchronous to the bus. It's also a lot more expensive.

 

[VMSZealot]

As I understand it, PiStorm replaces the 68000 on the board - making it only of use to Macs with a socketed DIP 68000. Surely it would be more useful/practicable to use the PDS slot?

 

[mikes-macs]

Without having any technical electronic hardware developmental experience at all, I think you have a interesting ideal and I'm surprised that more items haven't already surfaced using your idea. I had a thought years ago when some SE/30 owners were trying to wedge multiple PDS cards inside and then needed to deal with power and heat issues not to mention some cutting the chassis and case.

The thought that I had was, why not have an external setup for multiple PDS cards with a high-speed cable connected from a Pi inside external case that talks Mac PDS card language and another Pi connected to Mac's PDS that talks Mac PDS? Suppose you could also send SCSI through and install your favorite SCSI HD emulator inside the external case as well. Design a case that has 3 PDS slots and SCSI support.

Probably a crazy idea but perhaps it can be done.

 

[Powerbase]

For no good reason at all other than "because it's there", I was pondering the AST Mac 86 PDS card for the Mac SE, and it got me wondering whether it would be feasible to implement on a Raspberry Pi card, slotted into the PDS card of a Mac SE. Presumably, once a PDS to Pi had been developed, many other amazing things could be made to work through this functionality. Video boards. Accelerators. You name it.

Then I pondered if the same thing could be made to work for NuBus. A 386 or Pentium compatibility card, provided by a Pi, in the slot of a Mac II. A Radius Rocket more rockety than any rocket before.

I don't have the skill for this. It's just a pondering. But for people cleverer than me (just about everyone here), how feasible would this be?

I like the idea of a Pi-Rocket. You'd get a 'fairly' modern computer, that can directly interact with the Mac it's in. That'd be something I could get behind.

I personally don't care for the idea of the PiStorm. It's neat and I respect the work that went into, but I don't really understand the point of it. Once you start basically emulating everything in the system with the Pi, what's the point of the rest of the machine. Just gut the box and stick a Pi in there at that point.

 

[Melkhior]

Using a PDS slot instead of the 68k original socket doesn't make of a difference, maybe a bit more signal integrity issue but at the 68000 speed not really an issue. The PiStorm was designed for the Amiga, hence some of the choices.

Using the approach to make a peripheral instead of a CPU is quite doable. In fact it might be a smidge easier as you might get away with less comprehensive support for the bus protocol.

Ultimately it's not different from other device implementation for vintage system. What you need is
(a) a reliable interface with the bus (99.9999 % is nowhere near enough, as it's about an error per second on a 8 Mhz 68k...)
(b) some device behind this interface, memory-mapped adequately for the machine
(c) software support to get the device to work

Point (a) includes the physical (PDS, socket, ...) in addition to the logical (the bus protocol), and is usually just getting the appropriate connector (tough for the '040 PDS!) and designing the PCB. The bus protocol is the part where reliability might be difficult with bit-banging.

 

[MacSE/30]

How about using pi zero as graphics core instead of FPGA like ZTex in PDS or NuBus card?