Problem with FPU 68882

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Roberto
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Problem with FPU 68882

Post by Roberto » Wed Oct 13, 2021 9:16 pm

Hi everyone, I have just introduced myself to the new users area and now I am here to understand why the FPU 68882 purchased from the exxos site does not work on my Atari Falcon 030. In my Falcon there was a 68881 that still works today regularly (see first photo), I can use the functions dedicated to floating point math operations using DEVPAC 3, play "l'Abbaye des morts" which requires a mathematical coprocessor and perform the FPUREC.TOS, FPUTEST.TOS and FPUCHECK tests .PRG successfully with success. I wanted to "upgrade" my Falcon with a 68882, so I bought it on the Exxos website and it arrived a few days ago. I cleaned the pins well, so I replaced the 68881 FPU with the new 68882 one. Unfortunately, however, my Atari Falcon 030 fails at the time of the test lights (see second photo). Could it be the FPU with some problem or am I missing something?
PS: I again took out the 68882 and put back the old 68881 and it works.

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FPU 68881 work fine

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FPU 68882 no work

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exxos
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Re: Problem with FPU 68882

Post by exxos » Wed Oct 13, 2021 10:08 pm

They are all tested from my store, so unlikely to be the FPU. Maybe a RAM fault or bad socket ? The FPU program doesn't bomb on errors like that. Also clean the socket. Have you done the clock patches etc ? are you running a clean stock system in medium resolution ? screen you posted looks strange..
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Steve
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Re: Problem with FPU 68882

Post by Steve » Wed Oct 13, 2021 10:56 pm

Run from basic TOS and try again. Hold ctrl on boot. As Exxos says it would not bomb like that, fpu test by DML would just tell you certain tests have failed.

If it bombs in normal TOS then there is most likely an issue with your FPU socket. Buy contact cleaner, inspect the pins. Also check pins on your new FPU.

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PaulJ
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Re: Problem with FPU 68882

Post by PaulJ » Thu Oct 14, 2021 1:06 am

It would be my guess that a 68881 has a differient pal that the 68882. Just a guess.. When I put a 68882 in my MSTE from Exxos it needed a pal. Don't know about a falcon..

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Re: Problem with FPU 68882

Post by troed » Thu Oct 14, 2021 9:44 am

PaulJ wrote:
Thu Oct 14, 2021 1:06 am
It would be my guess that a 68881 has a differient pal that the 68882. Just a guess.. When I put a 68882 in my MSTE from Exxos it needed a pal. Don't know about a falcon..
The MSTE needs one for FPU or no FPU - but that's very different from the Falcon going from one FPU to another. Also they're addressed differently, with the MSTE needing I/O mapping (the PAL) while the Falcon's 030 does the lifting itself (FPU instructions).

I run a 68882 in my Falcon without issues.

regards,
Troed

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Re: Problem with FPU 68882

Post by troed » Thu Oct 14, 2021 9:48 am

13 Bombs
Coprocessor Protocol Violation. A read of the FPU has rersulted in a illegal value
https://mikrosk.github.io/doitarchive/doit_st/1905.htm

I interpret this not as wrong _value_ (calculation) but garbled data that doesn't follow the protocol between CPU and FPU.

/Troed

Badwolf
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Re: Problem with FPU 68882

Post by Badwolf » Thu Oct 14, 2021 12:59 pm

I second those that blame contacts.

I've being doing work with FPUs recently and I put back in one that I thought was broken and was about to bin and suddenly it passed all the tests.

I'd suggest your socket has grown use to the fit of the 68881 and is not quite mating with the new 68882 on all pins. You say you've cleaned the pins on the new chip? Perhaps they've been pushed a bit too flush to the package?

You could try flipping the chip over and using a spudger or flathead screwdriver, gently push the pins out a little bit.

I was about to bin two different chips that gave 13 bomb errors, but it turned out it was the DSACK1 line not quite contacting.

BW
Falcdate Use the internet to work around dead Falcon NVRAM battery
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
DFB External 030 and AltRAM for the Falcon (under development)

Roberto
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Re: Problem with FPU 68882

Post by Roberto » Sat Oct 16, 2021 11:35 pm

Badwolf wrote:
Thu Oct 14, 2021 12:59 pm
I second those that blame contacts.

I've being doing work with FPUs recently and I put back in one that I thought was broken and was about to bin and suddenly it passed all the tests.

I'd suggest your socket has grown use to the fit of the 68881 and is not quite mating with the new 68882 on all pins. You say you've cleaned the pins on the new chip? Perhaps they've been pushed a bit too flush to the package?

You could try flipping the chip over and using a spudger or flathead screwdriver, gently push the pins out a little bit.

I was about to bin two different chips that gave 13 bomb errors, but it turned out it was the DSACK1 line not quite contacting.

BW

I only quote your post, but in reality I am responding a little to everyone who wrote to me to help me.
These days I got to work. First of all I inspected the socket and the new MPU 68882, then, with the help of a needle, I perfectly aligned all the pins, pushing them a little outwards, in order to facilitate contact with the pins of the socket. I cleaned both the FPU 68882 and the socket with a specific high evaporation cleaner for contacts. I inserted the FPU 68882 into the socket, checking from an magnifying lens, then I pressed firmly trying to settle the FPU with my thumb, verifying at the end that all the contacts match (on sight because with the tester I could not enter them inside). I reassembled the power supply etc. and then connected the whole. When I turned on I held down the CTRL key, in order to have a clean system with no frills. In all graphic resolutions (Low, medium, high), both FPUTEST.TOS, FPUREC.TOS, FPUCHECK.PRG, but also my assembly program that performs some small floating point operation with DEVPAC3, it gives me error (3 or more bombs depending on the program, see photos). There is a modification to the motherboard (shown in the picture) that (in another forum), I was told that it is the modification of the clock and that of the sound. Both modifications were carried out by specialized personnel prior to the sale of the Falcon. It must be said that I have low NVRAM battery, but I don't know if this will affect. When I put the FPU 68881 it does not give any problems, in any resolution and with any program loaded at boot (see photo). Any help or advice is really appreciated. Thanks.

The careful work of cleaning the contacts

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Inserting the FPU 68882 (checked with the magnifying glass)

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Errors with various test programs

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Error compiling my simple assembly program

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By inserting the FPU 68881 instead it works, it never gave errors.

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This is my board patch

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exxos
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Re: Problem with FPU 68882

Post by exxos » Sat Oct 16, 2021 11:46 pm

As said before, the clock patch is probably to blame. It drives the FPU clock and the rest of the system. You seem to be getting ram corruption trying to use the FPU. The FPU test does not bomb, it shows errors. But bombs mean system corruption somewhere.as the FPU can't really corrupt ram , the common thing is the clock patch.
https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~

Badwolf
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Re: Problem with FPU 68882

Post by Badwolf » Sat Oct 16, 2021 11:52 pm

Three bombs? Not seen that before with FPU.

Good work with the cleaning -- you've at least concentrated on the most likely and the simplest fix.

I'd offer to test your 68882 for you, but I've become so untrusting of that damned FPUs infrastructure*, I wouldn't be confident of being able to!

To be honest, at this stage, if you've got a 68881 that works, I'd stick with it. Count your blessings! They're a nightmare.

BW

*EDIT: that previously read 'of that damned chip'. That could have been read to unfairly cast aspersion on Exxos' chips. That was not my intention. I've come to the opinion that if you put a chip in that socket and get it working *never breathe on it again*!
Falcdate Use the internet to work around dead Falcon NVRAM battery
Smalliermouse ST-optimised USB mouse adapter based on SmallyMouse2
DFB External 030 and AltRAM for the Falcon (under development)

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