Mega STE FPU upgrade

[troed]

For no apparent reason I'm thinking of upgrading my Mega STE with an FPU. Having read up on the subject I'm planning to get a 68882 - but when I look at my MSTE it doesn't fit the Atari installation instructions perfectly. Am I looking at a machine where there's already been one and the resistor sometimes found on the bottom side of the motherboard (non-W3 revisions) now being topside in the socket instead? I.e, the only thing I would need to do is to install the PAL there, besides the actual FPU.

From: http://www.atariworld.org/files/docs/C3 ... -REV-A.pdf

mega_ste_fpu.png

mega_ste_fpu.JPG

/Troed

[troed]

Alright, thanks to some images I found when searching it seems the answer is yes.



http://gtello.pagesperso-orange.fr/mste_f.htm

[troed]

(Anyone wants to sell me a programmed GAL? The FPU seems easy enough to source from China but I have no GAL programmer .. )

edit: sorted - many thanks guys! This is a very friendly scene

[mikro]

Yes, you only need the GAL. I've got mine from krupkaj (Honza Krupka), you can find him on AF, too.

[Greenious]

While I would recommend a 68881 in ST/STE, due to compatibility, the PAL code is available if you can find someone to program it for you.

Code: Select all

PART NUMBER: C301903©001
DEVICE: PAL 16L8©25
LOCATION: UB01 
CHECKSUM: $1221
TITLE: FPU CONTROL (FPUCTL)

”PIN	NAME			PIN	NAME•
1	FC0			11	A10
2	FC1			12	XFPUCS
3	XUDS			13	XIO
4	XLDS			14	A15
5	A5			15	A14
6	A6			16	A13
7	A7			17	A12
8	A8			18	A11
9	A9			19	XFPUDS
10	GND			20	VCC

À
JNÀ/XFPUCS	=	/XIO * A15 * A14 * A13 * A12 * A11 * /A10 * A9 * /A8 * /A7
			* A6 * /A5 * FC0 * /FC1

/XFPUDS	=	/XUDS + /XLDS

[troed]

While I would recommend a 68881 in ST/STE, due to compatibility

I read a lot of discussions on that subject, and there's one or two pieces of software (one GFA Basic version I think) which do not work with the 68882 but as far as I could figure out everything else works with a 68882, which is also per clock cycle a lot faster.

If I got the wrong impression and there's a lot of software that doesn't work it would of course be good to know.

/Troed

[Greenious]

Yes, 68882 is 50% faster.

Well, its mostly those that run into problems that tend to voice their issues, but in the past I've had quite a few hunting for 68881 because of problems... Otoh, 68882 is easy to source, 68881 is not in comparison, and it is easy to swap if need be... so it's not that big of a deal.

In the end, what matters is that the programs that you use can handle the 68882 correctly.

[double-decca]

Hi

I have a MSTE, without a FPU, does software run faster or does FPU specific programming fone

[alexh]

The only reason i can think of to have an FPU in a MegaSTe is to use more electricity

[Ragstaff]

I have a 68882 and a Mega STE, but never got the GAL sorted. Are there people who can help out with that?
Or should I just put it in the Falcon instead...

[Atari030]

Get one for the Falcon too, Tom. I have one in everything that I can fit one in, except my MegaSTE. It might be time.

[troed]

The only reason i can think of to have an FPU in a MegaSTe is to use more electricity

The only reason I do it is because there's an empty socket and I can

/Troed

[Atari030]

Behold, the great motivator.

[troed]

Thanks to @joska I now have the needed GAL as well as a 68882 in my MSTE. I've so far found no benchmark applications that actually use it though so I'm unsure whether it works It's detected by some apps as an I/O mapped FPU (SFP004 compatible and/or 68881).

Interestingly enough, even though the MSTE had a resistor topside in place of the PAL, it also had a resistor doing the same job on the underside of the motherboard. I was there repairing a trace for HD floppy support anyway and found it before testing, luckily enough.

mste_sysinfo.jpg

mste_gembench.jpg

/Troed

[frank.lukas]

Use GEMBENCH 4.03 ...

[troed]

Use GEMBENCH 4.03 ...

mste_gembench4.jpg

Many thanks for that! Seems to work fine.

/Troed

[guus.assmann]

Hello troed,

The results / speed can be increased.
It is very possible and not so comlicated to overclock a FPU.
My 16Mhz rated 68882 works just fine @33Mhz.
Faster was useless, as the passing of data is now the limiting factor.
Many PLCC 68882 devices are rated 40Mhz or more. This will help.
Just make sure the FPU doesn't get too hot.
BR/
Guus

[troed]

Hello troed,

The results / speed can be increased.
It is very possible and not so comlicated to overclock a FPU.
My 16Mhz rated 68882 works just fine @33Mhz.
Faster was useless, as the passing of data is now the limiting factor.
Many PLCC 68882 devices are rated 40Mhz or more. This will help.
Just make sure the FPU doesn't get too hot.
BR/
Guus

The FPU itself is a 40MHz variant, but I don't know how to overclock it in place on a Mega STE with the rest of the system in sync.

/Troed

[frank.lukas]

The FPU can work asynchronous in all machines an Speeder Cards ...

[guus.assmann]

Hello Troed,

Just disconect the clock line to the FPU and feed it with a highr frequency.
That's all it takes.
It may not be very simple to get the clock pin freed, I'm not sure how it's connected on this particular MB.
So you may have to cut some more traces, as the clock micht be connected to other chips and the trace could go "two ways" from the FPU clock pin.

BR/
Guus

[troed]

Just disconect the clock line to the FPU and feed it with a highr frequency.
That's all it takes.
It may not be very simple to get the clock pin freed, I'm not sure how it's connected on this particular MB.
So you may have to cut some more traces, as the clock micht be connected to other chips and the trace could go "two ways" from the FPU clock pin.

The FPU can work asynchronous in all machines an Speeder Cards ...

Thanks, both. In effect that means that @exxos' FPU OC for Falcon is really more general: http://www.exxoshost.co.uk/atari/last/FPU/index.htm

Sounds like a fun thing to do, even though I'm not sure I'll ever run any programs actually using it

/Troed