Need explanation of the CPU and FPU technology on turbo boards

[kidkoala]

I have a few questions about cpu's on accelerators;

I have a cd32 with sx32mk2 (think it's a 40Mhz cpu), I bought a fpu@33mhz, and i bought a crystal@33mhz as well.
Now, can you people explain to me;

1. what is the connection between the fpu and the crystal? (something about synchronous/asynchronous?), and can i just put in the fastest fpu and crystal there is? (says something about max. 33mhz in my primitive papers on the sx32).

2. can i put in the fastest cpu i find? (like a 50mhz or something), is there a connection between the cpu and the fpu speed?

3. what commands or programs do i use to find out the speeds that are right now? and how do i overclock the cpu/fpu?

4. what is the fpu used for (i know about floating-point operations, but what is that, and give me some examples of which programs/games use it and which doesn't)?

hope someone wants to answer all this, please give thorough answers if you do:) thanks a lot!

[alexh]

kidkoala wrote:
1. what is the connection between the fpu and the crystal?

For 68882 FPU's the crystal speed is 1:1 to the FPU speed. Use a 40MHz Crystal, FPU runs at 40MHz etc.

can i just put in the fastest fpu and crystal there is? (says something about max. 33mhz in my primitive papers on the sx32).

It depends on the accelerator, but in general YES.

2. can i put in the fastest cpu i find? (like a 50mhz or something), is there a connection between the cpu and the fpu speed?

The 680x0 and FPU can run asynchronously, but I believe that the CPU has to feed the FPU both instructions and data and so if there is a BIG gap between speeds (14MHz 020 & 50MHz 68882) then the FPU will spend a lot of it's time waiting. There is pipelining in the FPU so it's not a 1:1 relationship.

4. what is the fpu used for (i know about floating-point operations, but what is that, and give me some examples of which programs/games use it and which doesn't)?

The answer is mainly nothing. Very few games will use it. A few CAD like things (SCALA, Lightwave etc.) will use it.

[Hyperspeed]

Hang on, I thought quite a few games used it?

Does software specifically have to call on an FPU or will the FPU just cooperate to un-burden the CPU's task of dealing with floating point maths?

With the '040/060 the FPU is internal so it might be different with the '020/'030 CPUs...

I wonder if Shapeshifter/Fusion and other emulators use it. It's a shame there wasn't a SnoopDos tool that let you know exactly when a program used the FPU.

[keropi]

Only 1 games needs the fpu afair, a flight sim, maybe it is tfx? can't remember now...

[kidkoala]

thank you all for the quick reply!

that made it a bit clearer..

[alexh]

Hyperspeed wrote:
Hang on, I thought quite a few games used it?

Not to my knowledge. A handfull if that. Usually ports like Quake etc.

Does software specifically have to call on an FPU or will the FPU just cooperate to un-burden the CPU's task of dealing with floating point maths?

The code has to have been written to use an FPU or a maths library.

With the '040/060 the FPU is internal so it might be different with the '020/'030 CPUs...

Games dont use the '040/060 FPU any more than a 68881/2

I wonder if Shapeshifter/Fusion and other emulators use it.

I think that they do. But the question is "Does any MAC software of that day use the FPU?" I think it is just as unlikely.

[Hyperspeed]

The dissapointing thing I discovered was that using the FPU version of the MPEGA library was vastly slower than the integer version. I couldn't make out any difference in sound quality. Those using Songplayer or MakeCD's MP3-CDDA function would best stick with the integer (standard) MPEGA library version.

I'm sure I read that Gloom Deluxe, Breathless and Alien Breed 3D (/2) used the FPU. I mean, Alien Breed 3D 2:The Killing Grounds had polygon, texture mapped weapons, light sourcing and all that like Quake. Come to think of it, latter-day FPS like Genetic Species surely had some support for FPU?

I'm sure I heard of a few things that used FPU on 68k Mac too, wouldn't Quark have used this for complex object scaling? I'm sure Wordworth installed maths libraries...

It would make interesting reading which applications did use maths libraries. Would they be these:

mathieeedoubbas.library
mathieeedoubtrans.library
mathieeesingtrans.library
mathrans.library

?

Archiving tools like LHA too!

[Piru]

@Hyperspeed

Archiving tools certainly do not use FPU, at least not for anything time critical such as compression or decompression.

[AmigaMance]

@Hyperspeed

Archiving tools certainly do not use FPU, at least not for anything time critical such as compression or decompression.

 I don't think that WordWorth and any of the games that Hyperspeed mentions is using the FPU.

[KThunder]

fpu support was kind of like hd support back in the day but less critical. when a large percentage of amiga users had unexpanded a500s and a1200s or 2000s requiring fpu would cut out a large number of users and lots of potential profit.
68k cpus do integer math quite well so most programs could make do without fpu. libraries should use them though, if available.
iirc divide was the only 16bit math instuction the 68000 had (16bit divided by 16bit resulting in 32bit answer). many programmers especially demo coders and other assembly people used tables.

[Piru]

iirc divide was the only 16bit math instuction the 68000 had (16bit divided by 16bit resulting in 32bit answer).

Actually divu/divs was 32bit / 16bit -> 16r:16q, with 'V' flag set if the result would overflow 16bit.

[kidkoala]

well certainly I didn't expect such thorough and detailed answers

thanks a lot, though you're loosing me on the topic of "the
math instructions of the 68k"

[Piru]

To recap: FPU isn't really required for most things. If you really must run some scientific precision math things, or say for example render high precision mandelbrots or 3D scenes, you might want one. Then again, with these applications you're better off with 68060 and integrated FPU anyway. ;-)

[Hyperspeed]

I'm sure I had an archive of the LZX/LHA programs where there were FPU versions...

The only way to prove/disprove is to make a list.

So far we have:

Apps
¯¯¯¯
1) Lightwave
2) MPEGA

Games
¯¯¯¯¯
1) TFX

Demos
¯¯¯¯¯

Emulators
¯¯¯¯¯¯¯¯¯

:inquisitive:

[kidkoala]

here is an interesting article from the year of the lord 1999, considering the effects of an fpu, though in cooperation with three different patches;

http://www.youngmonkey.ca/nose/articles/NewTekniques_9902/ImprovingPerformance/index.html