Duo Dock/Duo Dock II - 68882 FPU Accessible Using a Duo That Has a 68LC040?

[Paralel]

If one is using Duo Dock/Duo Dock II  with a 68882 FPU installed, is it accessible using a Duo that has a 68LC040 for a CPU? I've always heard that the 68LC040 can't be used with a 68882 FPU, but I can't find any mention or errata regarding the 68LC040 based Duo's, such as a 280c, not being able to access the FPU when docked.

 

[beachycove]

My DD is not functional any more, and my 280c works only intermittently, but my recollection is that 'no' is the answer. Once upon a time, I spent time testing such things.

You get the same result using a 68882 FPU on an LCPDS card in an LC475 or the like -- no workie.

 

[johnklos]

The '040 doesn't create the proper bus traffic on floating point instruction traps.

 

[Elfen]

Which is strange, because the 68K - '030 is supposed to multi/co-process up to 7 FPUs at the same time and yet this function was not ported over to the '060.

Now why would anyone want to have 7 FPUs on their system with their main processor? "To Take Over The World, Pinkie!"

 

[Paralel]

That's what I thought. I came across a page that indicated it was possible, but it was only mentioned in passing, it was obviously just a mistake on the authors part. Full '040 or go home it seems.

 

[techknight]

Well considering the majority of the Duo line was 030 except for the 280 and 2300c, it made since for them to have an FPU in there compatible with the 030. 

 

[Paralel]

Yeah. I was just curious if it had some kind of secret sauce in it that allowed it to work or something. Sonnet announced a 68882 FPU add-on for the PDS slot in the Blackbird series of Powerbooks, but as far as I'm aware, they don't exist, and the fact that it's impossible would explain that.

 

[johnklos]

An m68881 or m68882 can be implemented as a peripheral, just like on an m68000:

http://www.retro.co.za/68000/MotorolaPDFs/AN947_REV0.PDF

However, you'd have to write your own SANE package that calls the FPU as a peripheral - floating point instructions wouldn't work.

 

[Paralel]

Easy to see why it was never done. Isn't doing it that way significantly slower than accessing the FPU directly?

 

[rezwits]

Wow!, never knew this... (FPU/040/DDII)

So the the Duo Dock II is only needed if you have a 210, 230, or 250?

Weird!

 

[Bunsen]

Uh.... no.  I'm not sure what you mean exactly, but the Duo Docks are compatible with all models in the Duo range (barring the space clearance in the lid for some models).  Every function in the Dock apart from the FPU is available to all models.

 

[rezwits]

What I am saying is "needed" meaning if you have any Duo other than a 210, 230, or 250, you might as well just get a regular Duo Dock? and not worry about getting the Duo Dock II for it's FPU right?

Laters...