Re: [f-cpu] "Tree"

[Bruno Bougard <bougardb@imec.be>]

Kim Enkovaara wrote:

> > Professional IC designers always work top-down, from spec to gate level,
> > through different abstraction level.
>
> That is also my impression. I'm currently part of a huge chip project and
> always the works start from specifications at top level by systems people
> and ASIC chief designers. After that chief designers try to partition the
> design to meaningful and reasonable sized blocks. Then designers can take
> that abstraction level and divide their own blocks to smaller blocks. Only
> after that should even coding start. If you start from the bottom the top
> level picture is very difficult to achieve especially in very complex
> chips. CPU is not usually very complex chip compared to some telecom
> chips, there top-down design is a necessity.

It seems that we come from the same world ;-)

> Of course this top-down approach needs experience about what is possible
> and some experiments during planning. Also some blocks need to be defined
> at least at pipeline and clock cycle level to see if something is even
> possible with given start parameters.
>
> > After P&R, when you have your back annotations, you can run again the
> > annotated netlist simulations (for the functionality) and the timing
> > analysis with the wire load model extracted from the lay out.
>
> Also in todays advanced flows P&R software can automatically change some
> cells in critical paths to faster ones and do all kinds of trickery to
> achieve the timing. You don't have that visibility during synthesis. The
> netlist after P&R is not usually the same you gave to the vendor.
>
> > synthesizer for IC and it is quite reliable.  I think other more or less
> > 'exotic' tools  such Alliance focus more on FPGA and other toy devices.
>
> I think Yann is not talking about Xilinx Alliance. He is talking about a
> tool made in french university. It has some resemblance to first versions
> of Synopsys in the beginning of 90s. Very small subset of VHDL87 supported
> and very limited capabilities.

You are right, I was confused by 'Xilink Alliance'. I don't now this French
university tool

> > Synopsys is quite expensive but some universities get 'educational
> > licenses', if there are student amongst you ...
>
> As far as I know the educational licenses are very cheap. It should not be
> a big problem for universities. Of course problem is to teach people to
> use them. Synopsys DC for example is pain in * to use. Synplify ASIC is
> much nicer and very easy to use. But it has to make some track record
> first, it seems to be a very good tool.

I also knew synplify as fpga synthesizer. I've just discovered it as ASIC
synthesizer. It looks nice. I'll try to convince my boss to go for a trial
with one of our design.

Bye
Bruno

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