Author: Johan Klockars (as12-5-4.kp.g.bonet.se)
Date: 01-20-2002 02:02
> Oh, you took it seriously? Sorry then.
I did not take anything on that site seriously.
> We are NOT going to tie several CPUīs
> together.
I understood that you did not want to use the '060. My point was that the entire idea of trying to use a separate processor to run some instructions was silly. It is obviously not needed.
> Though, haveing a ī882 for completion of the
> uncomplete FPU in the 040, is not
> impossible.
The '040 FPU is not uncomplete, it is the 68881/2 that did more than a decent FPU has any reason to do. Back in its day (15 years ago or so), implementing those functions in microcode probably made some sense, though.
Of course you could connect the '882 externally, but since it can not be used directly by the processor, you will still need to emulate the missing instructions in a way. That way will be by talking to the external chip, as the 68000 machines had to do when using an FPU, rather than using the built in FPU to calculate the functions, though.
The FPU functions missing from the '040 (and about every CPU on the planet except for the x86 (but not SSE/SSE2/3DNow)) are not often used ones. The performance will be better when called as library functions rather than illegal instruction traps too.
> > The '040 FPU is somewhere around ten times
> > faster than the 68882 at the same clock
...
> Thatīs right, and whatīs the options?
> Emulation!
> You did see that FPU benchmark?
Try running some real software rather than a stupid benchmark that no doubt does lots of trigonometric and logarithmic functions.
The GEMBench FPU benchmark is really terrible, but I don't know anything about the one used on that site.
> The world is full of cheap modern electronic
> circuitry -Why shouldnīt we use it???
Please do, but the 68882 is not modern, it's archaic. The possible performance benefit of including it on an '040 board will not be measurable, except possibly using some benchmark.
Anyway, it won't improve the compatibility in any way over the more direct approach at emulation, and the '040 will still not be 100% compatible with the '030.
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