[A83] Re: MirageOS remembering program location


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[A83] Re: MirageOS remembering program location




> So you say that pages $09 - $15 are only used for (fixed) data storage? Or
> has Ti some 'backdoor' which makes it possible for the ROM to execute from
> these pages?

...Err, no, not exactly.  08h-15h (08h-69h on the SE) are used for both
applications and user data archive.  The calculator can dynamically set
which pages it wants to allow code to run from (pages with apps on them).  I
haven't looked into detail on how this is done on the 83 Plus (though it has
to do with ports 5 and 16h), but on the SE it has a lower bound (every thing
below this will run), and an upper bound (everything above this will run) as
ports 22h and 23h respectively.  Apps are all loaded sequentially from high
pages down, so whenever an app is loaded to the calculator, the high bound
is updated to allow code to run from that page.  These bounds can only be
changed by when the flash protection is "unlocked", which can only be
accomplished by code running from pages 1Ch, 1Dh, and 1Fh.

> There are only 2 other RAM pages on the SE (next to the 2 normaly loaded),
> if I'm informed well. So what do you mean? It's, or the '3rd', or the
'4th'
> RAM page that let it also crash. So "some" is a bit wierd in this context
I
> think.

...You're not informed well :)  There are six other RAM pages on the SE
(other than the normal two).  That's why I said some.

-Dan Englender





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