( ESNUG 324 Item 2 ) ---------------------------------------------- [8/04/99]
From: Anil Kumar <anilk@vitesse.com>
Subject: Eleven Fundamental Troubles With Simplex's 'Thunder & Lightning'
Hi, John,
I saw there were couple of references to Simplex's Power analysis tools
'Thunder & Lightning' in your DAC'99 Trip Report. I have been working with
these tools for around an year now and I couldn't resist from commenting.
Though these tools have some good features or at least they try to solve a
few problems but then they have lots of problem too. Included below are
some of the problems/bad points for these tools:
* It has too many command/scripts/tools to do the required analysis
For e.g., If I were to do static IR analysis, I will have to go
through a run of at least 12 steps (which includes generation/running
of various scripts and tools)
* It uses many mystical or hard-to-understand the scripts/command files.
Generally, I just copy the old command file (which has a lot of Pascal
type statements). I just modify the new GDS design cells and couple of
file names without really having any understanding of the effect of
other statement in the command file. (In fact, that's what the Simplex
staff recommends.)
* You can't do power tradeoff analysis with this tool -- e.g. you can't
figure out which block is consuming how much of power and what kind
of peaking is going on with the chip's power.
* You can't really use this Simplex tool alone if you are planning to
design a power sensitive design. For power sensitive designs you need
information like: how is the power consumption distribution in
different blocks, what kind of peak and avg currents are drawn by
different blocks (and if you find something fishy, the tool should
provide capability to pin-point the cause of the problem e.g. block/
instances in higher level netlist). Simplex doesn't do this.
* Simplex uses a _lot_ of RAM/CPU power/disk space:
For RAM usage in a 350K design, their database generation tool
needed ~32G memory.
For disk space in that same 350K gate design, it created ~4.5 Gbyte
files on an IR and EM analysis. However cheap hard-disk gets, it's
still an issue for me to have lots of 4.5 Gbyte files to store,
archive, update, and manage. Simplex should be more sensitive about
how much of disk space their database takes.
* Simplex wall clock run time needs help. The 'Thunder & Lightning'
manual says that it can generate a transient current waveform at the
chip level, but when I asked it to generate transient current waveform
data for ONE signal for a 300K gate design, I had following results:
Runtime : 15 hr
No of transient current waveform : 1
Simulation time progress : 46 ns
Size of the o/p data : 4.75 Giga bytes
I sent this information to them and resigned to the idea of doing any
type of transient analysis with Simplex tools. Simplex's response
to this problem was they will fix it in next release. I don't know
it's current status.
* They don't have support for multi-voltage design. Simplex's response
was to scale various part of the design accordingly, but that
doesn't give good/accurate result... first of all you might not have
a very good scaling value for various part of your design. So the
end result will be as good as your guesstimation. (Personally I
don't like their response/solution.)
* They can't support multi-clock designs unless all the the clocks have
a common base clock i.e. every clock must have a common denomination
frequency.
* I disagree with their peak current dynamic IR algorithm because it
won't give you real real-time (peak supply current) IR distribution.
* Thunder simulation does not support any type of analog element i.e you
can only use this tool with purely digital type design.
* Their user interface could use a lot of improvement e.g. reduce the
large number of steps, making command files clean and simple, make it
user friendly. I don't understand how could Simplex ignores such
important things.
You will need lot of hand-holding from Simplex's support to work with their
'Thunder & Lightning' power tools.
- Anil Kumar
Vitesse Semiconductor Corp. Camarillo, CA
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