[Coco] Re: [Color Computer] 68881/68882 & the CoCo

[Mike Pepe]

Gene Heskett wrote:

> Well, with all the setup, loads and readbacks being done at the coco's 
> bus's leasurely rate, I'm not sure it would be that much faster.  If 
> the FPU was running at its spec sheet clock speed, and not loafing 
> along at the coco's speed, it might be faster. I suspect one would have 
> to go ahead and do it before that question could be answered with any 
> authority though.

The FPU would of course run at it's native rate. The 68k bus is 
asynchronous, and the setup and hold times of a CoCo at 1.8MHz are far 
above minimums specified in the data book.

The setup time is an issue, but somehow I think it would still be a lot 
faster, especially on the trig functions.

Natively, it supports 8, 16, or 32 bit data busses and the ability to 
function as a native co-processor or as a peripheral, so, like I said 
before, interfacing it to the CoCo bus appears almost trivial.


> One things for sure, it would be an interesting experiment. :)

Sure would

> Just recall the 6309's integer divide (16 into 32, with 16 bit 
> remainders and dividends) operation is 39 cycles worst case, and its 
> wide mul operations is even faster, 29 cycles worst case IIRC.  Unforch 
> I don't think any of the math libraries have been optimized for that.  
> If I ever get curious, I'll do the trig library again, but stop it at 
> the assembly code stage and see if I can optimize it for the 6309, I 
> sense there might be a considerable speedup possible by doing that.

Well, You're talking integer. I'm talking about floating point. I think 
despite the effort needed to set the FPU up, it should still be tons 
faster, but we'll see.

-Mike