Conference hydra::amiga_v1

    You'll need a MMU, like the one that comes with the A2620 board
    or the one inside the 68030.
    
    Regards,
    
    <CB>

        Well, that raises a few questions then.
    
    1) Does this imply that you need memory expansion; that it will
    not work with the stock 1meg?
    
    2) If I get MMU from somewhere, will it work without the additional
    hardware? Will SETCPU?
        
    3) Is there a way I can get MMU to try this?
    
    Some games (the original ARCHON for example) require kickstart V1.1,
    so I would love to get this to work. It will also be great when
    Kickstart V1.4 comes out, as the last time the disk was out
    several months before the chip.

< Note 3343.2 by MSVAX::BARRETT "Who is Steve Dahl?" >
                                -< Thanks <CB> >-

        Well, that raises a few questions then.
    
    1) Does this imply that you need memory expansion; that it will
    not work with the stock 1meg?

>>  The memory expansion is not the critical piece.
    
    2) If I get MMU from somewhere, will it work without the additional
    hardware? Will SETCPU?

>>  STECPU V1.5 was designed for use with the Commodore A2620 and A2630
>>  coprocessor boards. It may work with other coprocessor boards, but
>>  there are no guarantees.
       
    3) Is there a way I can get MMU to try this?
    
    Some games (the original ARCHON for example) require kickstart V1.1,
    so I would love to get this to work. It will also be great when
    Kickstart V1.4 comes out, as the last time the disk was out
    several months before the chip.

>>  Yep, buy an A2620 board.

    Is there no way to boot a kickstart disk on a 2000 without
    a coprocessor board? It would seem to me that it might be possible
    to load kickstart somewhere in a 256k chunk of memory, then boot
    to it.

Re: .4

>   It would seem to me that it might be possible
>   to load kickstart somewhere in a 256k chunk of memory, then boot
>   to it.

No.  The problem is that Kickstart is a non-relocatable program
with non-relocatable data.  It has in it absolute addresses that point
to particular addresses in the ROM.  You can't just move that code
and data to another address and have it work.

SetCPU works by setting up the memory management unit to translate
all the addresses in the ROM space to point to the RAM that the alternate
version of Kickstart is loaded into.  After that, the system thinks that
the alternate Kickstart is located at its expected address.

    Is this possible without a co-processor, or does memory management
    require it?

    My understanding is that the 68000 by itself doesn't work
    well with an MMU.  Something about the interrupts which the
    MMU needs to issue.  I understand that early on Apollo among
    others built 68000 systems with two 68000's, one running a
    few cycles (one?) ahead of the other.
    
    - steve

    re: .6
    
    The double-68000 machines were designed that way for virtual memory.
    Problem with a 68000 is:  if there is a VM page fault in the middle
    of an instruction, there's no way to recover the internal state
    of the processor.  This was fixed on the 68010.
    
    re: adding an MMU
    
    The memory management unit sits between the processor chip and
    everything else on the memory bus (excluding other coprocessors).
    It translates processor addresses to memory addresses and introduces
    a performance hit to the system.  Motorola's MMU chip adds 1 cycle
    to every memory access.
    
    The reason it's on the A2620 card is to support Unix's virtual memory
    features.  SETCPU's Kickstart relocation feature is just gravy.
    But this is an expensive feature if you just want to have more than
    one Kickstart available.  Dave Haynie has said in public that the
    reason he put the feature into SETCPU was because a 68020-equipped
    Amiga ran slightly faster when Kickstart was in 32-bit wide memory
    as opposed to being accessed across the 16-bit backplane bus.
    
    If all you want is to have more than one Kickstart option, I think
    you should stick with the hacks that put extra Kickstarts into EPROMs
    and switch select between them.
    
    My hardware 2�.
    
    Wes
    

    re .6:
    Or buy a used Amiga 1000 to run the games that haven't followed the
    rules.
    
    regards,
    dennis
    

    For what it's worth, the 1.4 version of Kickstart will *probably*
    be relocatable, so you could use it w/o a MMU.
    
    Regards,
    
    <CB>