I have had some ongoing issues with the A2000. Initially it was a lot of weird shit. The upshot seems to be a dead SCSI card, and the MegaChip is faulty.
The SCSI card in question is an Oktagon A2008. It does some clever stuff like locking up the Zorro bus when it is plugged in. So, unusable.
The MegaChip is more interesting. It has got contact corrosion on the pins. Strange that they would use such dodgy crap on such an expensive product.
I took along the A2000 as dead to the local user group meeting: SAUG. The geniuses there diagnosed the above faults and cleaned the contacts on the MegaChip. So got it back up and running. But after a couple of days it died.
It is now consistently giving a green screen on boot. This indicates a RAM fault. In this case a Chip RAM fault. So the next step is to drop it back to 1MiB Chip by taking out the MegaChip and putting an Agnus straight back into the socket. And see what happens.
Hopefully, I can get it up and running, and drop in the Blizzard A2060. Part of a plan to get a 68060 based Mac.
Got AOS4 classic up and running on the A1200. The A1200 has Mediator + Voodoo 3, Terratec and Realtek 8029AG. So far I only have the Voodoo working. There's only 192MB in the A1200. Hoping to pick up a thinner 128MB module to fit the BlizzardPPC.
Apparently, the Realtek 8029AG might be supported with an update. But there are issues with the faster 8039 and sound cards as these use DMA. Elbox (makers of Mediator) did a clever hack which uses the Video card as a DMA buffer for other cards on the bus. So far this is not supported in AOS4.
Performance wise, it ain't no AmigaOne. It is noticably slower, not unusable, but slower. I have yet to test the 68k emulation extensively. Paula works however, as well as native video. And even more cool, it handles the BlizzardVision and Voodoo better than previous versions of AmigaOS. Switching between the two is trivial.
All we are waiting on, is better PCI support, and BlizzardSCSI support, since I have no clockport hearers I am using just a buffered IDE adaptor, no FastATA, SCSI would be fast. AND we hope, the SharkPPC.
I've been doing so research on this, looks like there are a couple of options.
1. Put a 68060 in a Mac. This is possible, there are socket adaptors for 68060s to plug into 68040 sockets. They are pin compatible, apart from your average 68040 running on 5V and the 68060 running on 3.3V. It looks like the socket adaptors are built to order, and they do cost a pretty penny. There is another, slightly bigger, snag: the ROMs don't support the 68060. The 68060 is missing some features of the 68040, and superscalar functionality can cause another set of issues. So, you would also need to edit the ROMs (and burn a copy and resocket them). A little more than I can do :(
2. 'Emulation' via an Amiga. This is rather more straight forward. What is needed is an Amiga with a 68060, and a copy of Shapeshifter (or Basilix, or whatever), and some Mac ROMs from a 68040 based Mac (a Quadra, or Centris, for example). And ideally, a Graphics card. I have most of this already. Now, the reason that this works without kludgy hacks is that 68060 accelerators are freely available for the Amiga, and more importantly, the AmigaOS allows 68040 calls to be translated to 68060 in software. This allows the 68060 to work with 68040 ROMs.
For number 2, I am waiting to get the A2000 back up and running.
Interestingly, the reason that 68060 accelerators aren't available for the Mac is (apart from the ROM issue, which could be solved in firmware), is that the PPC emulation of the 68k was pretty good, and PPC native apps appeared not long after. The 601 is pretty crap CPU, but a 603 or 604 can easily emulate a 68040@40MHz at full speed. The time it would take to get a 68060 to market (given the ROM issues) would be longer than the time it took for a combination of 68k emulation in PPC and PPC native apps to catch up.
So, I was wondering how much RAM you could cram into an Amiga and came across some interesting information. The address space for the CPU slot in the A3000//A4000 is limited to 128MiB. Interesting because the trapdoor slot in the A1200 has no such limit. Hence the BlizzardPPC (and the Blizzard 1260 + SCSI, for that matter ) can hold 256MiB.
It would seem that the CPU slot of the A2000 can accommodate at least 128MiB, and I suspect is limited to this.
So what about the other ~4GB that the 32bit 68k (full 68020+) chips can address? Well, the Zorro bus is where this address space goes.
The original 68000 Amigas had only the 24bit address registers of the 68000, meaning 16MiB. This was partitioned off for all the system functions, for example up to 2MiB for Chip RAM, another 256k-512MiB for Kickstart, some more for the AutoConfig ROMs etc, with some being 'Reserved'. (I found a complete map of this once, but alas cannot find it again). The upshot being that only 8MiB was available for Fast RAM, and indeed any other RAM (like Video RAM) which needed to live on the Zorro II bus.
This had some strange results. Autoconfig RAM needed to live in this 8MiB, so that if you added an accelerator (like 68030) then there was the choice between using Autoconfig for the accelerator's RAM, or loading a command on start up to add the RAM 'manually'. The A2630 uses Autoconfig for its onboard RAM. And since it would most likely live alongside an A2091 (with its optional 2MiB RAM) it came only in 2 and 4MiB options. So the A2000 might have 3 classes of RAM, 32Bit Fast, 16 Bit Fast, and 16 Bit Chip.
The downside of the A2630 being that it steals this autoconfig space that it doesn't really need. This can be a problem if you want to use some cards in your A2000 that have their own autoconfig RAM, like graphics and video cards.
The Zorro II bus is basically an extension of the 68000's bus, running at the same clock, same address space etc. A nice simple bus for expansion.
Things did change, however, with the first full 32bit Amiga: the A3000. The 68030 has 32bit address registers meaning it can address up to 4GiB. Of course, some of this is already reserved for Chip RAM, Kickstart etc. However, the A3000 gives a whopping 1.75GiB to the Zorro III address space. Much nicer than the A2000.
So in theory, in an A3000 you could have a shedload of RAM, but some of it has to live on the Zorro Bus. Of all the RAM expansions produced for Zorro III the biggest and baddest was the A3128 by DKB. This gave you up to 128MiB RAM using 72 pin SIMMs. Maxing out an A3000 or A4000 (or the floor sTanding variants), would give you at most 512-640MiB of RAM in your Zorros, 128MiB on the CPU card, 16MiB onboard Fast and 1-2MiB Chip. So 786MiB in an A4000T. If you use a 3rd party BusBoard with 7 Zorro III slots, you might get an extra 256MiB.
That's as good as it gets.
This is all about my on going fumblings with hardware. Regular entries should provide an indication of the depths of my obsession.
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