[A83] Re: 83p os
[Prev][Next][Index][Thread]
[A83] Re: 83p os
On Fri, 18 Apr 2003, Brandon Sterner wrote:
> Upgrade your calcs to the ti89 (or *shudder* the voyage200 ) the 68k has
> some protected mode stuff.
The bare 68K only has the supervisor/user mode distinction. In supervisor
mode you are allowed a few extra instructions that don't work in user
mode, such as changing the trace bit and interrupt level, and halting the
processor. But the plain 68000 doesn't have the ability for true memory
protection (unless an external MMU is attached) so no true memory
protection. This makes it rather easy to get into supervisor mode if you
really want to, since you can easily change the exception vectors so your
code is run on an exception (in supervisor mode, of course). The 68K
calcs do have their own minimal hardware protection to prevent writing to
the table, but that is easily turned off by changing just one bit of a
hardware register.
References: