Linux on TI89/92?

Linux on TI89/92?

Post by kcarn.. » Sat, 22 Apr 2000 04:00:00



The TI-89 and TI-92[+] are graphing calculators based on M68k processors(the
M68000). Noting that there is a port of Linux to the M68k line ofprocessors,
I was wondering if it is possible to get Linux on this one.Protected memory
may be a problem (does the M68000 have _enforcable_protected memory?), as
might be process switching and other low-levelthings. I have, however, come
up with a few ideas:* The LCD is a memory-mapped device. For more details on
how the LCDworks, see (I think) ti89.acz.org (if not that, go to acz.org and
findthe TI89 page).* There exists an open-source kernel called TEOS that you
can findsomewhere at ticalc.org. It is definately not Linux, but you can look
atit to see how some things are done.* The M68000 knows about interrupts, and
ti89.acz.org documents some ofthese interrupts. Obviously Linux would have to
install its owninterrupt handlers, and keep any processes from setting
handlers oftheir own. This may require virtualizing the processor (see
below).* Task switching could be handled by an interrupt handler. It would
haveto save the PC and registers (these are on the stack when the handler
iscalled), and then push back onto the stack the PC and registers for thenew
process before the RTE instruction.* To provide the process security normally
associated with Linux'sstability, it may be necessary to virtualize the
processor. The extentof this virtualization can vary, but what I'm thinking
about is a codepre-scanner like FreeMWare's (but of course for the M68k) that
wouldsearch a block of code for potentially restricted operations
beforeallowing it to execute. Yes this would slow things down significatly.
Ifthere is a protected mode in the M68000 that I am not aware of, thennever
mind -- that could probably do it. (Yes I know there is protectedmemory, but
simply setting one bit in one memory location turns this off.)* The keypad
will be difficult, but by no means the limiting factor.TI's AMS uses the 2nd,
diamond, shift, and alpha keys to extend thekeypad, and Linux can do the
same. It is possible to type on the keypadat a decent speed, though it is
rather difficult. We would have to findsome key combination that would act
like CTRL, ALT (META), TAB, etc.(there are already F-keys).* Simple
framebuffer for the LCD.* Link is a network adapter.It would be really neat
if we could do this. Contact me at kcarnold <at>yahoo (dot) com for comments,
suggestions, etc.Kenneth

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Linux on TI89/92?

Post by Michael Enge » Sun, 23 Apr 2000 04:00:00


Hi,

: The TI-89 and TI-92[+] are graphing calculators based on M68k processors(the
: M68000). Noting that there is a port of Linux to the M68k line ofprocessors,
: I was wondering if it is possible to get Linux on this one.Protected memory
: may be a problem (does the M68000 have _enforcable_protected memory?),

A plain 68000 doesn't have protected memory, but there's a version of
Linux that runs on MMU-less 68k CPUs - see http://www.uclinux.org

: as
: might be process switching and other low-levelthings. I have, however, come
: up with a few ideas:* The LCD is a memory-mapped device. For more details on
: how the LCDworks, see (I think) ti89.acz.org (if not that, go to acz.org and
: findthe TI89 page).*

ti89.acz.org is the correct address.

: There exists an open-source kernel called TEOS that you
: can findsomewhere at ticalc.org.
[...]
Hmmm, looks like a great site ... what a shame that the last TI calculator
I owned was (or probably still is - I'm not quite sure ;-)) a TI30 LED ...

Does the TI89 really have 2 MB RAM ? I don't think so - why should there
be only "about 188K bytes of user-available RAM (memory)" available ?
Running ucLinux in 2 MB should be possible, running in 188 kB impossible.

Best regards,
        Michael
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