Overclocking 68882

[desantii]

Is there a real benefit of overclocking the 68882? I have a 50mhz 030 board and the 68882 actually overclocks and works fine up to 66mhz(via changing crytals). What programs use the co proc? is it really worth overclocking?

thanks

[prowler]

Originally Posted by desantii

What programs use the co proc? is it really worth overclocking?

Hi desantii,

You might find some useful info in this thread.

[alexh]

Depends what you're doing with your FPU. If you're running a ray-tracer or something then maybe.

Almost nothing uses the 68882 FPU. No games. Very little workbench software. Unless you're running a ray-tracer then it is hardly worth even having it on your accelerator. It just eats electricity and puts out heat.

[Paul_s]

You'd better overclocking a Microwave to 3000w. That way you can have your McCain microchips in 1 second flat

[PowerPie5000]

Originally Posted by Paul_s

You'd better overclocking a Microwave to 3000w. That way you can have your McCain microchips in 1 second flat

Just don't watch it cook as your eyeballs will melt

[Thorham]

Originally Posted by alexh

Almost nothing uses the 68882 FPU. No games. Very little workbench software.

Any application that uses floating point math using AOS's standard math libraries can use the FPU when you replace those libraries with the FPU versions that you can find on Aminet. I haven't tried those replacement libraries, because I don't have an FPU, but people who do may want to give those libraries a go.

[prowler]

Good point, Thorham!

I noticed, when I was contributing to the mpega.library (WarpUP) problem thread, that the MPEG Audio decoder V2.4 libraries comprise FPU versions as well, so the FPU may also be useful for playing MPEG files.

[Ed Cruse]

Originally Posted by Thorham

Any application that uses floating point math using AOS's standard math libraries can use the FPU when you replace those libraries with the FPU versions that you can find on Aminet. I haven't tried those replacement libraries, because I don't have an FPU, but people who do may want to give those libraries a go.

The replacement libs are probably faster but the standard math libraries will use the FPU if present.

[Ed Cruse]

Originally Posted by desantii

Is there a real benefit of overclocking the 68882? I have a 50mhz 030 board and the 68882 actually overclocks and works fine up to 66mhz(via changing crytals). What programs use the co proc? is it really worth overclocking?

thanks

Most of my Amigas including WinUAE have FPUs, but I almost always compile my programs without inline FPU code. I said almost, I have written several programs that do very intensive floating point calculations in which case I compile 68020 + FPU. These are programs that even with WinUAE take as long as 10 seconds to do their thing and would take minutes if not hours to do without the FPU.

The FPU is nice to have but like previously said not much uses it.

[alexh]

Originally Posted by Thorham

Any application that uses floating point math using AOS's standard math libraries can use the FPU when you replace those libraries

I'm open to hearing about applications that use such libraries. Ones that I might use day in day out without knowing. I'd like a surprise or two but I doubt there will be any but I am listening. In addition I guess they (obviously?) need to use the floating point parts of AOS standard math libraries to benefit? (Are the math libraries just floating point anyhow??)

Originally Posted by prowler

MPEG Audio decoder V2.4 libraries comprise FPU versions as well, so the FPU may also be useful for playing MPEG files.

MPEG Audio decoder ran at an unusable speed on my 68030@25 + 68882 (an A3000). Even on low settings.

[prowler]

Originally Posted by alexh

MPEG Audio decoder used to run at an unusable speed on my 68030@25 + 68882 (an A3000). Even on low settings.

Even when using the mpega020FPU.library?

[alexh]

It was not MPEGA.LIBRARY it was just MPEGA but I'm 80-90% certain I would have been using the correct optimised version for the A3000 if there was one.

It couldn't decode mono 128Kbit fixed bit-rate MP3's at 22KHz in real time.

This was a long time ago, maybe 12 years ago (1997/98), but I doubt MPEGA has been optimised much in all these years?

mpega020FPU.library (which is not what I used) is described by the author as potentially slower than MPEGA and it's code has not been touched in 10 years. But as I said, it was not what I used.

EDIT: After reading a bit I think MPEGA is fixed point only. But you have to take into consideration what the author of MPEGA.library says

Originally Posted by stephane.tavenard

Please, note that FPU versions are more accurate
than integer ones, but they consume more CPU !!!
So, don't e-mail me that mpega.library is slower
than mpega before you read this !!!

[prowler]

Originally Posted by alexh

It couldn't decode mono 128Kbit fixed bit-rate MP3's at 22KHz in real time.

You're right - that's pretty deplorable!

The lack of any distinct advantage to be gained by most users makes you wonder why provision for the FPU was a relatively common feature of Amiga accelerator cards.

Originally Posted by alexh

mpega020FPU.library (which is not what I used) is described by the author as potentially slower than MPEGA.

And that makes you wonder why he bothered, unless it was just proof of concept!

[Ed Cruse]

Originally Posted by alexh

I'm open to hearing about applications that use such libraries. Ones that I might use day in day out without knowing. I'd like a surprise or two but I doubt there will be any but I am listening. In addition I guess they (obviously?) need to use the floating point parts of AOS standard math libraries to benefit? (Are the math libraries just floating point anyhow??)


MPEG Audio decoder ran at an unusable speed on my 68030@25 + 68882 (an A3000). Even on low settings.

The standard Amiga math libraries are strictly floating point.

[alexh]

Originally Posted by prowler

that's pretty deplorable!

I wouldn't say deplorable. Just unusable.

This tool is pretty much a try once and never use again tool. (At least for me) Which I think is like most of the other FPU enabled programs.

I'm still open minded to hearing about a bit of software (one we all use all the time) which benefits from the FPU. Perhaps one we just didn't realise uses it.

The odd demo when you run it says "FPU required" and doesn't load. And these are times you wished you had an FPU.

I know because my A4000 originally had an LC040 with no FPU.

However when you look closer, most of these demos are marked "060 recommended" and suck on anything less. As I found out when I got my full 040

[rkauer]

Originally Posted by prowler

<SNIP>

The lack of any distinct advantage to be gained by most users makes you wonder why provision for the FPU was a relatively common feature of Amiga accelerator cards.
<SNIP²>

It's easy to do at design level: the FPU share the very same address and data paths as the CPU. Just route a pair of extra lines from one to the other.

OK, it puts more complexity when designing the physical board (routing) and require at least four layers. But all Amiga accelerators have four layers.

[prowler]

Yes, that would explain it. Thanks for clearing that up.