Re: [f-cpu] "Tree"

[Yann Guidon <whygee@f-cpu.org>]

hello,

nicO wrote:
> I have just read the package from Whygee and i have found an horror :
> specific entities for trees.
a binary balanced tree for buffering signals, yes.

> We don't need that.
it is indeed useful in certain circumstances.

> Synthetiser could recognise the loop and transforme
> it using a tree. It's automatic and balanced depending of the time used
> for the signal to come. I know that synopsys write a whipe paper on it.
> But it's old ! I have verified it.

1) never trust a compiler/synthesiser, unles you can look at the output
2) if you don't like it, you are not forced to use it :
don't compile it and the default architecture will be fine.
3) Synopsys is not the only compiler on earth. We try to be as open
as possible to other EDA toolchains which may not contain smart
optimisations. If we design code only for Synopsys then it could be
useless with other tools. On top of that, it is not even monetarily
free... which explains why few people have ever accessed it.
4) if the compiler is smart enough to understand what the fanout
tree does, then it is able to do a better work. Otherwise, we have
a minimal failsafe. I am thinking of the "extreme case" if we have
to use Alliance as a last resort...
5) Evaluating the fanout's "cost" is necessary, otherwise our
"time budget" will not hold. When writing in RTL/HDL,
one does not necessarily "see" that an operation requires a large
fanout and this counts in the design budget. A "hidden" fanout
tree can slow the clock frequency down if it is not identified.
At least we can hint the synthesiser to balance the fanout before
or after a pipeline stage bareer.

I know that "advanced" tools can do they work nicely but
we have almost no chance to use one. If i can skip the "pseudo-VHDL"
part of Alliance, a lot of thing will remain to do manually, such
as place/route through C files... It's probably the ugliest thing
ever, but Alliance has (only) 2 good sides : it works and it's free.
The rest is horrible but at least i can use Alliance.
Does anyone know another solution ?

> nicO
WHYGEE
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