[A83] Re: 83p os

[Prev][Next][Index][Thread]

[A83] Re: 83p os

right a poor design, this relies on the programmer of games to be
responsible enough to do that... besides a mem reset would also disable the
os.  anyone care to factor a 512 bit number?

brandon sterner

----- Original Message -----
From: "Jeff" <telepath75@hotmail.com>
To: <assembly-83@lists.ticalc.org>
Sent: Monday, April 14, 2003 10:46 PM
Subject: [A83] Re: 83p os


> Depending on how its configured, all that would need to be done is IM 2
> after the romcall.  Unless, of course, the user is accessing flash in the
> TI-OS, then am interrupt-resident program would be disabled.
>
> > problem with writing this sort of os for the 83+ is that you'd can't
write
> > to flash without calling a romcall and these romcalls switch to im 1.
> >
> > brandon sterner
>
> > > I had this idea once, but wasn't ambitious enough.
> > >
> > > The TI-83 doesn't exactly have a "boot."  However, the TI-OS uses the
> z80
> > > interrupt mode 1 (IM 1) in handling interrupt routines.  This
indicates
> > that
> > > upon an interrupt, the calc should call code at $0038.  However, $0038
> is
> > in
> > > ROM, and cannot be manipulated!  Interrupt mode 2, though, can be
> > configured
> > > to handle interrupts nearly anywhere in memory.  What you need to do
is:
> > >   -disable interrupts
> > >   -set interrupt mode 2
> > >   -set the I register to the most significant byte of a page-aligned
257
> > > byte
> > >     buffer
> > >   -fill the 257-byte buffer with the same byte, referring to an
address
> > with
> > >     the same byte in each significant place (for example, $9393 or
> $9494)
> > >   -install interrupt code at the specified address (for example, $9393
> or
> > >     $9494), starting with EXX / EX AF,AF' and ending with EX AF,AF' /
> EXX
> > /
> > > RETI
> > >   -enable interrupts
> > >
> > > That is a quick overview of interrupts.  What do you mean by the TI-OS
> > > files?  I recommend reading intguide.txt (focused on TI-83+, remember)
> and
> > > asmhelp.zip, found on ticalc.org, to learn about interrupts and the
VAT
> > > (variable allocation table).  If you have any specific questions feel
> free
> > > to ask!
>
> > > > Hi...
> > > >
> > > > I'm going to write a mutitasked os to my ti83p. Does anybody know
how
> > > > the ti-os files are stored and what addresses are called on
> > > > boot/interrupt?
> > > >
> > > > TIA
>
>
Follow-Ups: References: