Games/demos known to be hard to emulate?

[spotUP]

That alcatraz demo would be interesting to test. Which part was it? And which alcatraz demo? I or II?

[spotUP]

COOL FRIDGE by UPFRONT, gives me a black screen on the problematic part, nice find.

[thellier]

This is Alcatraz Mega Demo II
In the last part that start with the message "this part only works in a1000"
If I remenber well (last time i saw it 25 years ago on an A1000...) on A1000 there are vector graphics (things like rotating cube) in the midle of the screen

If remenber well what said an alcatraz coder called DarkBlitter " one of our craziest coder has tested several unused 68000 opcodes and had found one that do a math operation that serve to optimize this demo"

[StingRay]

Originally Posted by thellier

If remenber well what said an alcatraz coder called DarkBlitter " one of our craziest coder has tested several unused 68000 opcodes and had found one that do a math operation that serve to optimize this demo"

That's typical coder humour. There are no illegal/undefined 68000 opcodes. I don't remember that there was anything special with the last part when I made the WHDLoad patch some years ago, I'll check when I'm back home.

[meynaf]

Originally Posted by thellier

If remenber well what said an alcatraz coder called DarkBlitter " one of our craziest coder has tested several unused 68000 opcodes and had found one that do a math operation that serve to optimize this demo"

I tested all unused 68000 opcodes many years ago and they all trap as illegal.

[ReadOnlyCat]

Originally Posted by meynaf

I tested all unused 68000 opcodes many years ago and they all trap as illegal.

Good to know, thanks for sharing.

How many words of operands did you test with? I guess you had to choose an arbitrary limit just in case an illegal opcode used more than one word?

[meynaf]

Originally Posted by ReadOnlyCat

Good to know, thanks for sharing.

How many words of operands did you test with? I guess you had to choose an arbitrary limit just in case an illegal opcode used more than one word?

As the 68000 traps as illegal by checking the first code word only, it's pretty safe to test just that (some 020+ codes are wrongly executed on '000 because of this).