arnljot wrote:
1) What can make the card incompatible with Classic amiga PCI boards
I am making an assumption that there was a technical problem Elbox couldn't overcome without a new Mediator. The economics if they could have made it work speak for themselves, the markup was to have been from $59 to $400! It would have been enormous for Elbox, they will have done everything they could to make it work!
I am not 100% "au fait de" with PCI topology, but I think the Mediator is a Zorro III to PCI bridge and in order for there to be another CPU on a PCI bridge, the Mediator has to be a Zorro III DMA master to allow the PPC to be able to initiate access to Amiga RAM. I am 99% sure that no Amiga PCI bridge cards are DMA masters. Even if they were I doubt very much if the PPC could access anything else other than RAM, I doubt it could access the registers in the custom chips for example.
But why would this matter? Surely it could work the other way around? The PPC could run happily just transferring data between other PCI cards? I can see that might work. But to interact with the host Amiga it would need some shared memory in the PPC's PCI space that the 680x0 could post to, to give commands etc.
Well I bet such a scenario, while perhaps possible under the PCI specification, was never tried before Elbox released Mediator. Asynchronous DMA transfers between two PCI "masters"? Maybe that did not work? Collisions etc.
All pure speculation, unless we get someone in Elbox to talk to us... just pure speculation, and probably bad technology on my part.
Michael Boehmer of E3B would be the best man to consult, he knows this stuff inside out having played with both Zorro III DMA and the Prometheus DMA.