68020+ support

[Yulquen74]

When writing programs, typically in C, for Amiga with 68020+ as target,
is there more to it than compilation flags and maybe some inline assembly?


For existing programs that lack 68000 support, would many of them work
with just a re-compile for tat CPU, or is the situation more nuanced?

[Thomas Richter]

Huh? The 68020 assembler is a superset of the 68000 assembler (except one instruction, but that's not used by compilers anyhow). Which means that if you write programs in assembler, and you want them to run on any 68K member, you can only use 68000 instructions. If you want it to run faster on the 68020+, you can also use 68020+ instructions - but it then works on the 68020+ only.

For compilers, it is quite the same - you can tell them what the target platform should be, and that determines which instructions they can use. Sometimes avoiding or enabling certain instructions or scheduling instructions differently can also help to improve the execution speed, e.g. bitfield instructions on the 68060 are relatively slow compared to other instructions. Some compilers have options to use a particular instruction subset, but still schedule instructions such that the code runs (slightly) faster on the advanced members without using their instructions.

Anyhow: There is no need to recompile code designed for the 68000 to run on newer members, and generally, you do not have the sources for recompilation either.

[Photon]

Originally Posted by Yulquen74

When writing programs, typically in C, for Amiga with 68020+ as target,
is there more to it than compilation flags and maybe some inline assembly?

More to what? Sounds like you want to port AmigaOS utilities from a non-Motorola CPU? Then there's more to it. E.g. AmigaOS4 PPC apps, AmigaOS4 will have added some library functions (or entire libs) and maybe an app relies on them. You will then have to bring that support over to 68k as well.

If the program targets AmigaOS < 4 and is written entirely in C, there should be no problem recompiling it.*

Inline Assembly (for a non-Motorola CPU) will have to be translated to 68k or C.

Originally Posted by Yulquen74

For existing programs that lack 68000 support, would many of them work
with just a re-compile for tat CPU, or is the situation more nuanced?

This sounds like fixing "forgotten" 68000 variants of existing C programs. Now that there are 68000 CPUs running faster than 68EC020, this is a good idea. (Actually, it's a great idea no matter what, and I heartily support it! )

If there's a 68020 version there isn't much; typically if the program changes SR (Status Register), accesses words/longwords at odd addresses (allowed on 68020+), or relies on stack frames being a certain fixed size, you will have to have a look.

Inline 68020 Assembly might use one of the few extra instructions here and there, but these can usually be easily rewritten (for a performance loss ofc, reason for making new CPU models innit?)

So set to 68000, recompile, test. If you find something fix it. Shouldn't be too much.

* Usual C compiler caveat, it usually finds some reason to not compile innit?

[Yulquen74]

Thanks.

Photon: Yes, adding 68000 support to existing C programs to run on fast 68000 systems was what I had in mind when asking those questions.

[Don_Adan]

Then the only good solution its reasembling existed 68020 execs.
All other solutions will be only partially works or will be very slow.
You can start f.e from Dungeon Master 2 and creating 68000 version of exe.

[Photon]

Originally Posted by Yulquen74

Thanks.

Photon: Yes, adding 68000 support to existing C programs to run on fast 68000 systems was what I had in mind when asking those questions.

Very nice, greatly appreciated! I'm setting up network on ACA500Plus and ofc compatible drivers are included with X-Surf, but I tried to set it up generally beforehand to get some practice and those libs/components (e.g. AmiTCP4) I've tried so far have actually had a 68000 port.

There was a time when this wasn't so and Aminet was full of useful programs, but only if you had a 68020+.

I would say graphical web browsing is not practical with anything less than a 68060. And many websites will be bloated even in text mode. But e.g. Lynx is one that lacks a 68000 port (on Aminet), and might be useful in conjunction with a collection of non-bloated useful information sites, HTML versions of .guides, etc. Unfortunately no mention of Amiga sources on the official website.