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[f-cpu] Too much option



Hi,

   I am currently working on a new release of the manual with the new color 
code for ISA and an OP_CODE map. I discover that we have 2048 possibles 
versions of the F-CPU, because we have a lot of optionals instructions.
All the immediate form are optional, mix/expand/sdup are optional too. For me 
they must be include in all F-CPU compatible chip and we must reduce the number 
of possible version of F-CPU chip. I agree that LNS and FPU must be optional, 
but for increment based operation I think it's really too much usefull to be 
optional.
   What did you think about this problem ?

   I update shift instructions too and I discover that they have 2 unused bits. 
Why not using them to say :
  00 => double shift right
  01 => shift right
  10 => shift left
  11 => double shift left

The problem will be with immediate, in that case we can use 2 operandes one for
normal shift the other for dshift. (rot instructions have 2 unused bits too, so
we can use them in the same way). It can save a lot of OP_CODE. (I quickly 
count them, and we have approximatively 100 different OP_CODE).

  For the next release I want to insert widen instructions, but I read in a 
precedent mail that michael didn't like the way he describe it or something 
like that. Is it possible to have a little description on them ?

Cedric

PS: Yann I am waiting for your new ROP2 instructions list...
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