Chuck Rock 1, compatiblity issues on Amiga 1200 ?!?

[gimbal]

What is 'game crawling'? Frame rate issues?

[Galahad/FLT]

Originally Posted by Foebane

Is this minor change (with a simple fix as described above) the reason that Chuck Rock (and many many A500 games) were listed as incompatible with the A1200? As listed in Amiga Format and other magazines?

Honestly, didn't these game developers know about the A1200 differences? Or didn't care?

WHDLoad has been a revelation in that regard, with easy fixes to existing floppies!

I also wondered, when AGA came out, if the incompatibilities were due to the chipset, but apparently not.

Chuck Rock is overall a well coded game, just an overly complicated way to setup supervisor mode and it failed, not because of AGA, but 68020.

In developers defence, they probably thought of an Amiga A500 the same as a Spectrum or C64, I.e. no significant revisions, and when sales start to fall off, Commodore will simply develop and release a new machine that likely has no connection to the A500 at all, so programmers didn't necessarily worry about owners of big box Amigas with processor cards, because they would represent such a tiny minority of people that bought games, their target was to ensure rhe A500 was well catered for, as that is the biggest volume machine.

[malko]

All books I have read said that the instruction set was the same disregarding the 680x0 CPU (meaning that 68010 -> 68060 use the same base as the 68000)
But here I understand that a 68000 instruction can have a different meaning on a 68020. Is that correct?

[Galahad/FLT]

Originally Posted by malko

All books I have read said that the instruction set was the same disregarding the 680x0 CPU (meaning that 68010 -> 68060 use the same base as the 68000)
But here I understand that a 68000 instruction can have a different meaning on a 68020. Is that correct?

68020+ have some extra instructions not present on 68000, but thats not why in this instance Chuck Rock failed.

When an Amiga crashes, it will put important details on the stack, and does them in a specific format when 68000 is the cpu. You can also put stuff on the stack and pull stuff off the stack (like parameters etc, return addresses).

However, the stack format of 68020 is slightly different, and this is where Chuck Rock failed, the code only assumed 68000, in which case moving stuff onto the stack would have been predictable, on 68020 the difference in the stack frame format means that the predicted result was no longer valid, and so it crashed.

I think someone was over complicating a quite easy job, that was understood how to do easily and without problems.

Lots of programmers didnt mess around with stacks in such a direct way, they would push and pull register contents to the stack and not do anything else with it, which means their code will work no matter the stack frame format.

[gimbal]

It sounds like that even if you program directly against the hardware on an Amiga, you can still go too low-level

[malko]

Thanks for the precisions Galahad

[dlfrsilver]

Originally Posted by Galahad/FLT

68020+ have some extra instructions not present on 68000, but thats not why in this instance Chuck Rock failed.

When an Amiga crashes, it will put important details on the stack, and does them in a specific format when 68000 is the cpu. You can also put stuff on the stack and pull stuff off the stack (like parameters etc, return addresses).

However, the stack format of 68020 is slightly different, and this is where Chuck Rock failed, the code only assumed 68000, in which case moving stuff onto the stack would have been predictable, on 68020 the difference in the stack frame format means that the predicted result was no longer valid, and so it crashed.

I think someone was over complicating a quite easy job, that was understood how to do easily and without problems.

Lots of programmers didnt mess around with stacks in such a direct way, they would push and pull register contents to the stack and not do anything else with it, which means their code will work no matter the stack frame format.

and the game was programmed on Atari ST for the Amiga too (68000 only).

[Galahad/FLT]

Originally Posted by dlfrsilver

and the game was programmed on Atari ST for the Amiga too (68000 only).

Not remotely relevant to the issue being discussed

[DanScott]

Originally Posted by dlfrsilver

and the game was programmed on Atari ST for the Amiga too (68000 only).

I don't think so... Core had SNASM devkits at that point

[Galahad/FLT]

Originally Posted by DanScott

I don't think so... Core had SNASM devkits at that point

And 1991 is especially pertinent, not only was it the year Chuck Rock was released, pretty sure Seeing is Believing was the same year and that was programmed using SNASM wasn't it?

[redblade]

Originally Posted by Galahad/FLT

And 1991 is especially pertinent, not only was it the year Chuck Rock was released, pretty sure Seeing is Believing was the same year and that was programmed using SNASM wasn't it?

But surely at this time the publishers must of being complaints or games returned from the big boxed amiga owners?

[dlfrsilver]

Originally Posted by DanScott

I don't think so... Core had SNASM devkits at that point

Premiere was developped on Atari ST for the Amiga, the main code has the ST executable word '601A' at the beginning.

[Galahad/FLT]

Originally Posted by dlfrsilver

Premiere was developped on Atari ST for the Amiga, the main code has the ST executable word '601A' at the beginning.

Are you telling him or asking him, he programmed it lol

[gimbal]

Originally Posted by Galahad/FLT

Are you telling him or asking him, he programmed it lol

This is why I love EAB.

[DanScott]

Originally Posted by dlfrsilver

Premiere was developped on Atari ST for the Amiga, the main code has the ST executable word '601A' at the beginning.

Premiere was developed on SNASM, no Atari's involved

[Galahad/FLT]

Originally Posted by redblade

But surely at this time the publishers must of being complaints or games returned from the big boxed amiga owners?

Let's be realistic, if you could afford a big box Amiga when new, do you really think a platformer like Chuck Rock is why you bought your machine?

Strategy type games or flight sims that installed on a hard drive yes, platformers....not so much.

[jotd]

from the start they had published a list that games that didn't work. People knew.

(then we whdload-fixed all of them )

[dlfrsilver]

Originally Posted by DanScott

Premiere was developed on SNASM, no Atari's involved

ok, but then how's that we get the Atari ST executable mark '601A' then ?

Sorry to bugger :P

[Galahad/FLT]

Originally Posted by dlfrsilver

ok, but then how's that we get the Atari ST executable mark '601A' then ?

Sorry to bugger :P

$601a is a standard 68000 BRA instruction, also valid on Amiga

[Don_Adan]

Originally Posted by dlfrsilver

ok, but then how's that we get the Atari ST executable mark '601A' then ?

Sorry to bugger :P

Yes, some Amiga games was assembled using DevPac (Atari ST version). For checking if this is Atari ST exe file you must/can check not only $601A at begining of file, but also relocs table at the end of exe file, are very easy to recognise.