[A83] Re: 83p os


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

[A83] Re: 83p os



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

----- Original Message -----
From: "Jeff" <telepath75@hotmail.com>
To: <assembly-83@lists.ticalc.org>
Sent: Monday, April 14, 2003 9:33 PM
Subject: [A83] Re: 83p os


> 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!
>
> Jeff
>
> > 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
> >
> > --
> > Max Sikstrom
> > pengi@molik.org
> >
> > MoLiK programming and demo group
> > http://www.molik.org/
>
>




Follow-Ups: References: