True FastRAM on miniMig

[wolfchild]

This is mostly a question/proposal aimed at the FPGA and PCB guys around here.

Looking at the original Amiga block diagram, one can see that ROM and FastRAM are connected directly to the 68k processor bus.  On the miniMig design these connect through a multiplexed bus, thus sharing bandwidth between chipset and CPU.

Now, considering that the whole 68k CPU bus is externally available, how about putting 2MB of real FastRAM on the CPU bus (and adding an expansion connector in the process)?  The ROM image could then be moved to this region of memory as well.  This would allow the RAM to operate at CPU speed rather than at the current chipset related speed.

From my knowledge, I would say that this should happen following such a mod:
1. Over-clocked 68k should run at full speed from FastRAM without having to wait out on the chipset.
2. Full 2MB chipRAM.
3. ROM access will be at full speed.
4. RAM timing will be more relaxed with possibility to use 12ns RAM and maybe slower without effect.
5. CPU expansion bus?
6. CPU clock which is not a multiple of the chipset clock, just to get that last ounce of over-clocking potential.

Seeing that the miniMig platform is picking up as a generic simulation platform, there should be the option of disabling the 68k while leaving the RAM operational.

What do you guys think?  Wouldn't it be a nice V3.00 miniMig?  (I'd call it miniMig 300...)

Edwin

[alexh]

It's possible but no-one is going to do it. Next gen FPGA boards (Such as the DE2) have a much bigger FPGA's, DDR access and no external 68k

If you cannot "bodge it" onto a MiniMig v1.1 board then I don't think anyone is going to do anything.

[Illuwatar]

The problem with that design is simple - it isn't a MiniMig anymore. You should look into the board presented at www.fpgaarcade.com instead. No idea that multiple designs doing almost the same appears. My idea is simple: two designs, one high-end (FPGAArcade) and one low/mid-end (MiniMig).

By the way, a 3.0 is in the plan. I'm working together with yaqube to make an "ultimate" MiniMig design that includes the ARM controller directly on the main board. Also, an expansion port for aux. devices and more RAM is planned. But it will still be compatible with the MiniMig 1.1 (with the ARM conversion kit from yaqube). Hopefully, that will be the last incarnation of the MiniMig design. FPGAArcade should take over from here with it's improved performance.

[wolfchild]

@Illuwatar
Now that's what I wanted to hear!

Are you planning to put expansion headers (same style/pitch as CN5 on your V2.0 PCB) on the  RAM and CPU buses?  That would open up the board design to all kinds of add-ons, while still remaining a miniMig.

I'll get a PCB as soon as you have a release! :-)

[Lorraine]

/

[Illuwatar]

Initially, it will be the Mini-ITX form factor as it is easier to pull this off with a dual layer board. But I may implement the ARM part into my Mini MiniMig too (that board needs to be re-done anyway due to the change of the SD-card holder). The original 12 x 12 design is Dennis - I'm not going to "steal" it from him (and it would require a 4-layer board to build it anyway).

[ChaosLord]

Does FPGAarcade output 24-bit video?

[wolfchild]

ChaosLord wrote:
Does FPGAarcade output 24-bit video?

Nope, no 24-bit.  It's 30-bit. :-D

That will be one mean piece of kit!