Re: A89: Re: Re: Re: Re: CORRECTION: Shift+ON
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Re: A89: Re: Re: Re: Re: CORRECTION: Shift+ON
the only place I can remember the unused bits of address being used is
in the main headers.
nostub.h:
asm("bset #7,(%sp) /* The support for ~exit~ and
~atexit~ */
jmp _main"); /* and the workaround for a bug in
TI-GCC */
doors.h:
asm("_main:bset #7,(%sp) /* The support for ~exit~ and
~atexit~ */
jmp __main");
and I am guessing, but I think that is used so that zeljko can remove
stack frames until he hits the one that is marked with the highest bit
set.
Note: never stick a number on the stack (with asm) with the high bit set
if you expect to be able to exit().
Johan wrote:
>
> On Sat, Aug 19, 2000 at 02:06:36PM +0200, Jean Canazzi wrote:
> >
> > Well, 256k is only 18 bits, so what does it have to do with the 24 bits
> > address bus of the 68000 ? For me, the fact that the 68000 only have a
> > 24 bits address bus just means that the higher byte will always be
> > ignored (btw, isn't this property used somewhere in TIGccLib ?).
>
> The RAM address range is only partially decoded and the RAM is repeated over
> and over again to fill the entire 2MB at $000000-$1FFFFF. However, the
> security chip lives in the range $040000-$1FFFFF.
>
> TIGCCLIB uses the fact that the upper 8 bits [of PC] are ignored in
> addressing. (I don't know why/when though. :) )
>
> /Johan
--
Scott "Wrath" Dial
wrath@calc.org
ICQ#3608935
Member of TCPA - tcpa.calc.org
PGP key available
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