[Coco] [Color Computer] Re: OS-9 as Replacement for DECB.

[James Diffendaffer]

>> James
>>
>> The Coco 3 uses floating point for all its math even addition. All the
>> floating point math can be off loaded from the interpreter onto a PIC
>> or and AVR at more efficiency to RSBASIC. Most of the routines
>> are bogged down by this.

> Along these lines, years ago someone got a 68881 working with a 
> CoCo.  Of course these are probably not readily available right now.

The 68881 uses a different floating point format than the coco
floating point.  A new Basic could be built around it and most
software wouldn't be the wiser.  The only software that would have
problems would be software that messes with the floating point numbers
directly.  The 68881 would probably offer better precision.

Again, I'm not sure how efficient the CPU to math chip interface would
be.  The PIC solution would probably be easier since you could support
the existing floating point format and it's more flexible. Both would
offer some speed enhancment but with the overhead I'm not sure how
much of that gain you'll actually see.  Since the floating point math
routines in the ROM are used by everything I don't think it would be
difficult to test this.

I do think there are ways to gain speed and maintain compatability
through software that will yield better results.  Avoiding the
floating point math and conversions whenever possible should yield the
biggest improvement for most Basic programs just because of the nature
of the ECB interpreter.  It constantly converts strings to numbers and
to/from flaoting point even if you have a loop on one line.

Adding instructions to a VHDL 6809 will be more effective than an
external math coprocessor because it eliminates some overhead. 
However, if someone wanted to develope and test the new instructions
without going to VHDL, the instructions could be trapped by a 6309 and
emulated with a PIC coprocessor.  That could be used to test different
instructions usefullness in speeding up the interpreter.  It wouldn't
give exact results but results could indicate where the biggest gains
will be and what instructions should be implemented. 
It's a lot easier to code on the PIC than in VHDL!





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