Re: C-128 and Jeri board

From: Professor Dredd (
Date: 2001-05-02 17:35:20


Absolutely not. JOS would have to be fully ported to
work without the SuperCPU. It is HEAVILY dependant
upon 65816 features not present in the 6502 CPU. It
relies upon these features to do multitasking.

LuNIX, however, already runs on a 6502. It will
probably run straight off. The only reason to even
mess with it would be to take advantage of the
advanced hardware of the J-board (sorry Jeri.) From
what I understand of LuNIX, that ought to be pretty
easily done.

I don't think Jeri has yet specified how the extra
memory is addressed. I suppose the simplest route is
to have it bank switched. If you think about it,
there's no reason to invent an entirely new standard
for something like extended addressing when one
already exists. 

If the 16Mb RAM is bank-switched, it would make sense
to use a scheme compatible with the C-128 banking
scheme. Just expand the MMU registers to their full
potential, giving us RAM0-RAM255. This will work
toward eventual C-128 OS compatibility and programmers
already understand it well enough. 

Of course the MMU will have to be further modded to
ensure it can remain mapped into the system under the
C-64 configuration. Should not be a problem if we're
creating the new MMU in digital logic rather than
silicon anyway. In this scheme, its almost like having
24-bit addressing, except that the MMU controls the
upper 8bits of the addy buss.

Another cool benefit of going this route is that it
gives the C-64 environment access to the other
features of the MMU such as relocateable stack and
Zero Page. That would be excellent for people doing
multitasking projects  :)

I don't see any point in trying to emulate a 16Mb REU
with the on-board RAM. We can always build a SEPERATE
16Mb REU to be added later  ;)

In the end though, I suppose there's nothing to stop
Jeri from simply adding 8-bits to the addy buss and
controlling it with her own logic either inside or
outside the emulated 6502. It's her project after all.

--- Bryan Pope <> wrote:
> Oh right... Hmmmm...  But J-board is supposed to
> come with 16MB.  
> So then the new CPU has 24 address lines or does
> bank switching.
> Now since the CPU is running a lot faster then a
> stock CPU (and 
> uses 24 address lines) JOS should be happy (Except
> for any 65816 
> specific code)

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