Above 512Kb memory adressing ?

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leonard
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Above 512Kb memory adressing ?

Postby leonard » Tue Nov 23, 2004 4:50 pm

Hi !

Tonight I just wanted to debug SainT to release a PASTI version running Union Demo, but I have a very strange bug. The union is now working under SainT but only in 1040. If I set to 520, the union protection crash. After debugging, I just see it reads a long above $80000 ( say $80010). To me, reading $80010 on 520 gets $FFFFFFFF 32bits value data.

Could anyone test it on real hardware ? ( I can't coz I have a 4Mb STE).
Thanks

( I'm sure union demo works on 520ST, but no emulators run it in 520 mode actually ). Or maybe the STX Union demo disk image is a very old one, only working on 520 ? I could'nt beleive that !! :-)
Leonard/OXYGENE.

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Postby Gunstick » Tue Nov 23, 2004 8:20 pm

reading unused memory does not give $ffff but some random data. It usually gives the data which passed just before over the bus (the move instruction code or $80010) but for shure it's not ffff or 0000

George

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Postby leonard » Wed Nov 24, 2004 4:55 pm

Ok could anyone with 512Kb, 1Mb or 2Mb atari St could run that little prg on real hardware and tell me exactly what's the text displayed on the screen ?

thanks !
Leonard/OXYGENE.

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Postby Gunstick » Fri Nov 26, 2004 7:29 pm

leonard wrote:Ok could anyone with 512Kb, 1Mb or 2Mb atari St could run that little prg on real hardware and tell me exactly what's the text displayed on the screen ?

thanks !


it shows one of 3 values at random:
$20082008
$0000FFFF
$00000000

Note that $2008 is the code for "move.l a0,d0" which is the next instruction coming after your reading memory "move.l (a0),d7"
MC68K prefetching...

Georges

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plop

Postby C-Rem » Fri Nov 26, 2004 8:36 pm

i've found on a real 520stf 512ko :

$0000 0000
$2808 ff7f
$2008 0000
$0000 ffff
$3f18 ff7f
$2008 ff7f
$3f08 ff7f

on a real 1040ste 2mo :

$0000 0000
$2008 2008

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Re: plop

Postby Gunstick » Fri Nov 26, 2004 10:29 pm

the variations may also be explained by bus noise, as those values are remains of data transited 2 or 4 clock cycles before there could be one or 2 bits which toggle value due to bus reflections, capacitor charge or anything else.
I say this because a newer STE seems to have less noise than the older STF.

If I get my STF to work (3MB heavily modified model) I will see how much noisy bits I get on thet one.

Georges

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Postby leonard » Sat Nov 27, 2004 3:19 pm

It's very interesting.

Hey gunstick, if you manage to run your 3Mb machine, you have to modify my ramtest2.prg. I just handle 512, 1MB and 2Mb machine. If I find more than 2Mb, I suppose it's 4Mb (witch is wrong in your case :-) )
Leonard/OXYGENE.


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