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jasonsbeer / Amiga-N2630

A re-imagining of the Amiga A2630 processor card.
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Enable Zorro 2 RAM In 68000 Mode #13

Open jasonsbeer opened 1 year ago

jasonsbeer commented 1 year ago

Currently, the Zorro 2 RAM on the N2630 is only available in 68030 mode. It should be possible to enable it in 68000 mode with little or no undesirable side effects.

Investigate feasibility and implement.

TheBajaGuy commented 10 months ago

Tossing in a comment - maybe something I touch on could help. I assume your Z3 RAM is your first AutoConfig PIC in accelerator mode. I'll then assume that the Z2 FastRAM PIC follows it. I don' know if you have a PIC for the IDE interface in that sequence somewhere, but I'll assume it could be. Upon selection of the 68000 mode, you would need to check that your RAM state machine remains active against the 68000 bus (and any buffers default to facing it as a slave). You would need to shut/jump over the Z3 RAM and/or the IDE interface PICs after _reset comes up. Also, read your 0MB and 4/8 MB card size jumper. A user would likely connect a DP(DT) switch to effect their choice of mode and/or possibly size.

I dunno if there is an available jumper for it, so due to possible complexity/limitations, it may need to be effected in the firmware - one for inclusion of 68000 fallback memory, and one that does not. The presence of the AutoConfig Fast memory can throw off some poorly programmed early games.

I don't have a card, but am considering getting one with the PGA FPU layout (if anyone else is getting a few boards made). I think I have a fair number of the parts already in my spares collection.