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Re: [f-cpu] Come back of loadcons



Michael Riepe a écrit :
> 
> On Sun, Aug 04, 2002 at 10:50:50PM +0200, cedric wrote:
> > Because no body continu the discussion about loadcons, I don't know if we take
> > a decision. For memory, Yann say that the shifted loadcons cost a lot in the
> > CDP and that's a reason to not implement it. For Michael "it only cost a mux"
> > in the CDP that currently always exist.
> >       From Thomas point of view it's better because of scalability reason and I
> > agree with him. If I resume all this different argument I can only go to the
> > conclusion that we must implement this loadcons.
> 
> There is a new argument: When we have `cshiftl', the old loadcons[x].4
> (and higher suffixes) and the new `shifting loadcons' are no longer
> required. Building large constants may take a little longer with cshift,
> but it is possible to populate the whole register, no matter how wide
> it is - and we need only two opcodes (loadcons.[0-3] and loadconsx.[0-3]).
> 
> The only remaining argument against the original loadcons is that it
> requires a partial write (that is, a feedback from the register read
> port and a mux inside the CDP). But that's true for the shifting
> loadcons as well, unless we use a `shadow register' implementation.
> 
> I think we should implement cshift and drop the shifting loadcons
> variant, as well as loadcons[x].[4-15].
> 
> Any objections?

nop !

For immediat data, i propose to add the idea to use 6 bits immediat for
each instructions (it does cost nothing more, you just use the field of
the register adress instead of the content of the register). I beleive
that's a lot of small constant could be used in real code. So such
immediat could be interresting (small multi dimentionnal array index
calculation, stack index management,...) !

nicO

> 
> --
>  Michael "Tired" Riepe <Michael.Riepe@stud.uni-hannover.de>
>  "All I wanna do is have a little fun before I die"
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