[TI-H] Re: TI-89 HW2 overclocking
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[TI-H] Re: TI-89 HW2 overclocking
Greg Dietsche wrote:
> just to make sure you are aware, allot of programs on the 68k calcs
> take advantage of the ram layout... by adding 0x40000 (256k) to
> pointers, some protections built-in by TI can be bypassed. Kernels do
> this as well as ppg (compressed) programs and event hooks...
> there is memory mapped io too...
If you look at the memory map, there is a huge "hole" from 0x3ffff to
0x1fffff
where the 256K ram is repeated. This is where the larger chip will reside.
Sice it is repeated normally, it means the chip gets chip select in all
of the range, because of that its a bit more simple to add larger ram.
The protection is a problem though, but I thought most of those bypases
by added pointer took place in rom areas of the adress space, and in the
port range.
But I'm not sure there.
if you put in "just" 1½M or so instead of the full 2M, you can do the
bypass anyway though by just changing the pointer offset in the old
programs, since the first part then will be repeated in the end.
> Yah, its 2 128k chips. You shouldn't use more memory then the m6800 in
> the 89 can address since that's just a waste of money. Does the Ti-89
> use all of its Addressing space?
> --
> S.D.
Ok, then you add two chips... or, replace them with a single is
probably the simplest.
68000 can adress 16M of memory, so no problem there. the ti89 uses only
a small part, 2M for flash, 256K for ram, and a few words for I/O.
And as I said, there is already room in the memorymap for extra ram.
Probably a design desicion from the designers of the TI89, so they later
could choose how much ram to put in it.
--Olle
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