Made an old-skool demo! - Page 10

phx · 25 November 2009, 13:12

Quote:

Originally Posted by StingRay

Why shouldn't it work? It's never executed on 68000 machines, code checks the CPU. I'm pretty sure it wasn't the cause of the crash when the code was assembled in 68020 mode.

You're right. I didn't look at the source. But then I want to know why it crashed at first. Maybe Jason can do a binary-compare of the two executables...

AmigaBoy · 25 November 2009, 13:32

Quote:

Originally Posted by phx

Maybe Jason can do a binary-compare of the two executables...

I've placed the 000 and 020 binaries into the zone. Both are compiled with the same command line. The only difference being the "opt p=68020" line being changed to "opt p=68000" and the ".get_vbr_code: movec vbr,d0" being changed to ".get_vbr_code: dc.l $4e7a0801".

The filesizes are different and there's too many changes between the files to know where to look. What I can see from a quick search is that the opcode $4e7a0801 appears in both executables at almost the same offsets so it's clear there's something else causing the crash.

StingRay · 25 November 2009, 14:19

I checked, problem is this:

Code:

	tst.l a0

in the replayer init. Apparently vasm optimized for 020+ in 020 mode which makes sense of course. If you disable any optimizations the problem should not occur anymore.

phx · 25 November 2009, 14:42

Quote:

Originally Posted by StingRay

I checked, problem is this:

Code:

    tst.l a0

in the replayer init. Apparently vasm optimized for 020+ in 020 mode which makes sense of course.

Yes, indeed! Good catch!
So it was just luck when assembling with the original Devpac, which doesn't perform that much optimizations. To be on the safe side I would suggest to switch to 68020 mode for the movec only:

Code:

        opt     p=68020
        movec   vbr,d0
        opt     p=68000

pmc · 25 November 2009, 14:46

Out of interest StingRay - what does tst.l a0 get optimised to on 68020+ that dies on 68000?

Quote:

Originally Posted by phx

To be on the safe side I would suggest to switch to 68020 mode for the movec only:

Good idea - I'll amend my new sources.

StingRay · 25 November 2009, 15:57

Quote:

Originally Posted by pmc

Out of interest StingRay - what does tst.l a0 get optimised to on 68020+ that dies on 68000?

tst.l ax is not a valid 68000 instruction (which is why it crashes on 68000). On 68000 you would have to do cmp.l #0,ax (which is the original code in the replayer init) or move.l ax,dx.

pmc · 25 November 2009, 16:02

Oh OK - yeah, I should know that really!

Thanks StingRay.

30 November 2009, 15:11

Hi All,

Wow, seeing all the old 68k code is great, never knew a site like this existed.

Keep up the good work, look forward to seeing the finished product..

25 November 2009, 14:19	#183
StingRay move.l #$c0ff33,throat Join Date: Dec 2005 Location: Berlin/Joymoney Posts: 6,863	I checked, problem is this: Code: tst.l a0 in the replayer init. Apparently vasm optimized for 020+ in 020 mode which makes sense of course. If you disable any optimizations the problem should not occur anymore.

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