created sam fv  9 05:57:51 GMT 2002 by whygee@f-cpu.org
version Tue Jul  2 05:51:53 CEST 2002

This directory contains the INC Execution Unit.
It is more or less designed as explained in the F-CPU manual,
except that there is no bit reversal, hence only 4 operations.
However it fits in 6 logic levels : 1) xor 2-4) 4-tree, 5) xor
and 6) mux. Supported operations are : INC DEC NEG ABS LSB0 LSB1

No priority encoder is built after the LSB tree. The output format
is suitable for use by the popcount unit so it's the way to go
(though it's a several cycles longer) if you want to align stuffs
or perform some priority encoding (ie sort the IRQs).

This part is contributed by Etienne Labarre.
I then modified it deeply to make it work like the other units.
IIRC, around year 2000, Erik Hansen tried to make INC but
never completed it. As it is well described in the manual,
this unit is not very complex to design, though.
As a souvenir, i included a proposal made by Micheal,
long ago... As with his designs, i added the support to this
unit for other tools and linked it to the rest of the CPU.
Some more peer review would be beneficial, as it could
better homogenize the interface, but it's another story...

YG
