( DAC 02 Item 20 ) ---------------------------------------------- [ 9/10/02 ]
Subject: Nassda, Apache, Nanosim, Celestry, Silvaco, EverCAD, FTL, Spectre
NEAR SPICE: This year's golden boy in the Near SPICE niche has been Nassda.
Not only does their HSIM do well, their IPO impressed a heck of a lot of
Wall Street investor types because of the incredable 114X return the early
investors in Nassda saw for their money. Synopsys Nanosim has been trying
to recapture these lost dollars to Nassda. The fact that Synopsys now owns
Avanti's HSPICE, makes the threat to Nassda even more evident. The new kid
on this block is Apache's NSPICE.
"I have been using Apache NSPICE for over a year. My thoughts:
(1) Accuracy, when we first use NSPICE we did many test cases, we find
the tool is very accurate, the output wave form is exactly same as
that of Avanti HSPICE. Even in non-accurate mode, the output is
still accurate enough for most of the analog circuits.
(2) NSPICE has a stress function, which is ultimately important in
today's submicron analog designs. The reason is that for a lot of
analog circuit, we use 3.3 V power supply, for some critical
transistors, such as opamp input diff pair, we have to use fast
0.15 um device, the maximum tolerable voltage across the 0.15um
device is around 1.65 V, so we have make under all conditions, the
maximum voltage across all node of 0.15 um device is less than 1.65
V, HSPICE doesn't have the capability of doing that, NSPICE can do
the stress check.
The stress check capability gives us a peace mind, otherwise if we
miss the stress on even if only one transistor, the whole chip will
start to fail after 1 year of operation, then it will be really a
nightmare.
(3) S-parameter is also good for us, NSPICE is the only tool can do it.
We got a lot of S-parameter data from customers' backplane, we need
to run sims to make sure our chip will work on these backplanes.
(4) We use NSPICE as a SPICE simulator, basically it can do all HSPICE
can do, additionally, it has features which can help us design
analog circuit easier. The interface and syntax of NSPICE is fully
compatible with that of HSPICE. So it is very easy to use.
(5) Compare to HSIM, NSPICE is not that fast as HSIM, because we use
NSPICE for accurate analog simulation, we don't expect NSPICE can
be as fast as HSIM."
- Shuran Wei of Analogix Semi
"CADENCE:
We are mostly a Cadence shop Virtuoso through Spectre through Silicon
Ensemble, although we do have tools from Avanti (HSPICE, and Hercules
what a wonderful tool), Sequence Design, and Innoveda. In our
experience, Hercules is significantly better then Cadence's Assura.
(We own both).
We came to believe that Spectre was receiving more emphasis then HSPICE
at the parent company and we found that Spectre was actually even
better supported at a critical BiCMOS foundry partner then HSPICE.
After fighting that battle for a year, we switched over to Spectre.
My biggest overall complaint is that Cadence does not support HPUX as
well as it does Solaris. Constantly we run in to problems (3 per year
or so) where we surface the issue to Cadence. What frustrates me is
that Intel is a huge HPUX user and I can't believe we are finding
things Cadence doesn't already know from Intel."
- Parker Robinson of Insyte Corp.
"Regarding SPICE, we use SmartSpice from Silvaco mainly for analog
design, but we also use HSPICE and Spectre. We use both Star-Sim and
H-Sim. We're starting to benchmark Celestry's UltraSim."
- Zenji Oka of Ricoh
"Silvaco sells a large number of specialized tools, including layout
design tools, DRC/LVS, schematic capture, circuit simulation, parasitic
extraction and process simulation tools. Their big news this year is
that all of their tools run on Linux (note Tanner is on Windows)."
- John Weiland of Intrinsix
"Although Nassda positions themselves as the third generation fast SPICE
simulator, it really addresses the similar problems as Synopsys NanoSim
and StarSim. Nassda may have accuracy and capacity (from hierarchical
and highly repetitive designs such as memory), NanoSim has a lot wider
spectrum by integrating with their behavioral & digital simulator VCS.
It'll be interesting to see how NanoSim & StarSim eventually play out."
- Weikai Sun of Volterra
"Synopsys Nanosim is good. We have migrated our old EPIC tools to
Nanosim on Linux. Will keep using their solution. Nanosim has also
some good features like mixing different design levels (SPICE+Verilog)
in one sigle run."
- [ An Anon Engineer ]
"Mixed Signal / High Capacity tools:
Pretty much same old, same old. The spin on 'which is better StarSim
or NanoSim?' just got confusing. Both teams claim they are compatible
tools, however the NanoSim product just makes a lot of the wrong
technical choices for mixed signal interface at 90 nm and below. I
think the StarSim product is better organized and coded -- and since
they are now shipping with the same device cores as HSPICE, you can
kill off 3-6 weeks of 'accuracy' benchmarking.
It was good to see that they did not run the same faked benchmarks as
last year where everyone ran the same block on the same 3 clients and
then toggled the switches on their tools so they won the time race.
Everyone also admitted that if you want accuracy it really whacks the
tool and most of the speed goes out. This isn't all bad. Without
these tools you could never load and get an answer from a 10K+ element
device run - even if it is not fast.
The big loser in this race seems to be Mach from Mentor. I do not see
much market traction on it or even people talking about Mach. It's
pretty good technology. I think it just got lost without a marketing
thrust and it was too late to join in the race with just good/stable
code but NOT great code.
A new player that is pretty cool is the EverCAD Audit tool. It's a
mixed SPICE/Verilog tool that plays hierarchy to get capacity. Their
tool is cheap compared to HSIM and StarSim and they are claiming it
kicked Nassda's butt in a couple of big Japanese accts and took the
seats. I would believe that because EverCAD Audit is fast, and since
it reads Verilog in addition to SPICE. In the big post layout netlists
that you check with the Nassda/Synopsys tools, you have to translate
your vector set to a SPICE waveform input test bench to run a sim. On
EverCAD you just feed it the Verilog waveform data as you did in
digital sim. Both the Star guys and the HSIM guys say this is no
biggy, but I know a number of very large accts who have NOT gone to
high capacity SPICE simulators for this very reason. EverCAD had 3
folks at DAC, and they have been around for while selling code in the
Far East. This is their first US exposure. Small company, good tools,
good people. I hope they stay at least a couple of years to mature the
product before they get sucked up. EverCAD looks like a good fit to
the Cadence products as they are the biggest guys without a high
capacity simulator offering."
- Pallab Chatterjee of SiliconMap
"23.0 SPICE-like simulators
Antrim Design sells a simulator that takes SPICE and Verilog AMS. They
say their table-driven SPICE is about 2X faster than Cadence Spectre,
which their tools hook to.
EverCAD sells a table driven simulator for SPICE and Verilog. They say
they can handle about 50K transistors in their SPICE-like mode and
about 1 million Verilog gates.
Celestry sells a table driven SPICE-like simulator that they say is
1000X faster than SPICE."
- John Weiland of Intrinsix
"I like Nassda better than EPIC tools which have always suffered from
poor software quality and the cumbersome setup/human interface. Who
knows about Avanti's Star tools? Not sure if they have good R&D in
all those areas."
- Jai Durgam of SiImage
"VENDOR: Nassda
TOOL: HSIM
TOOL PURPOSE: accelerate transistor level circuit simulations
such as Avanti HSPICE.
OVERALL RATING: 4 stars out of 5
COMPARABLE TOOLS: Avanti/Synopsys StarSim and Cadence ATS. In our
experience, HSIM was more accurate and significantly faster.
APPLICATIONS:
SOC integration verification, Custom Memory Design, Analog
Circuits (PLL), CMOS and BiCMOS technologies
OUR EXPERIENCE:
We had decided some time ago, that for an SOC integration flow, the
ability to simulate actual transistors could prove a strategic
advantage in verifying our designs prior to silicon release.
Our initial goals were modest: establish functionality of each block.
For this purpose we purchased Synopsys/Avanti's StarSim. This tool
was very successful for us until we noticed a particular accuracy
problem with a large macro. While working with Synopsys/Avanti to
resolve the accuracy problem, we evaluated HSIM and found that it had
significant advantages in accuracy and performance. Subsequently we
purchased several licenses of HSIM.
HSIM is now integrated into our full custom design flow. We use the
Spectre models as the reference "golden" simulator, but HSIM is so
much faster that our process is to now use HSIM in the direct design
flow. We first assemble the Spectre model (or cross section as
required), we run comparison runs with HSIM to establish accuracies,
we iterate through HSIM, we close with Spectre.
We also use HSIM in places where it is not possible to use Spectre.
We view that HSIM is an incredibly valuable tool when integrated with
the Cadence Artist Tool flow.
We are well satisfied technically with the tool.
We are well satisfied with Nassda as a vendor.
AREAS for IMPROVEMENT:
(1) Extraction Flow Cookbooks
Nassda, in our opinion, could further the sales opportunities of this
tool if they would focus energy on working through the extraction flow
with various other vendors of extraction tools. These flows should be
pre-debugged and provided as a simple "cookbook" to customer prospects.
This would save significant time and we could have benefited greatly
from such a service.
(2) Model Interpretation
In addition, Nassda should canvas existing important foundries for
example model types and model coding styles and ensure that the tool
can interpret these models without any manual or Perl script
pre-processing. It is highly desirable to use models "AS-IS" from
the foundry. The issue is not a show stopper but it is an area for
improvement. See discussion below.
CRITICAL FACTORS (you might not think of):
(1) Standard Cell Schematics
One obvious point: for use of this tool in an ASIC flow it is vital,
of course, that the vendor supplying the standard cells is willing to
provide circuit schematics. This is not always the case if your
vendor is enforcing a "black box" LVS flow.
(2) Models
Some foundries are able to supply you with device models that involve
the use of "if else" statements and support Monte Carlo analysis.
This is highly desirable. In most HSPICE environments, people use
combinations of specific model files following a structure similar
to: FastN_FastP TypicalN_TypicalP FastN_SlowP. HSIM handles these
kind of models easily. The more advanced Monte Carlo style statistics
or skew files present a problem for HSIM. Perl scripts can be written
to modify the foundry models into an automatic form that HSIM can
accept, however it does take effort.
(3) Extraction Flow
It is very important to debug the extraction flow as one of the biggest
uses of HSIM is to analyze the effect of RC parasitics. We use
Columbus-Gold/Columbus-RF from Sequence Design with Synopsys/Avanti
Hercules for extraction re-processing.
(4)Reviewing Results
Large simulation runs require the use of binary output viewers. The
default output format is ASCII and this method may take from minutes
to even hours to load a useful set of waveforms. This is why a binary
viewer is so important. HSIM has a tool N-waves which is very helpful
in that it can process the binary waveform outputs."
- Parker Robinson of Insyte Corp.
"My company uses Nassda HSIM heavily. We have 2 copies of it, and at
times, it is in 100% usage, especially right before tape-out. (We
have 6 copies of Avanti HSPICE, also.) Using HSIM's hierarchy rather
than HSPICE's flat-mode lets us run many simulations quickly with
minimal loss in accuracy. It allows for full chip simulations of our
devices which are 10's of millions of transisters. HSIM is especially
useful when debugging first silicon. When new problems develop, we can
see in simulation what went wrong.
However, we have not had a new release of HSIM in the past year, which
in the EDA market is amazing. Yes, we pay maintainance on our 2
copies. Also, we recently bought a new Sunfire computer, and the
license transfer fee from Nassda was close to the most expensive of
everyone including Cadence, Avanti, Synopsys, and Celestry. (Celestry
was the most expensive license transfer, followed by Nassda.)"
- [ An Anon Engineer ]
"We especially prefer Nassda HSIM over Avanti HSPICE when:
1) The netlist is bigger than a few hundred transistors
2) To avoid HSPICE's dreaded convergence and "time-step too
small" problems
3) We need the simulation results in a hurry (a few hours
instead of a few days)
We've used HSIM for years. HSPICE is more accurate, but, as far as I
am concerned, HSIM is accurate enough. HSIM is 5 to 6 times more
expensive, but you get what you pay for."
- San Lin of Quadrant
"My design engineers here at National (and before at AMD) have used
Nassda's HSIM. At AMD, we used HSIM for full-chip simulations of flash
memories, which are mixed-signal devices which have control logic,
sense amps, and charge pumps on the same chip. We found HSIM to be
easier to use than PowerMill, since it did not require a config file.
It gave a better speed vs. accuracy trade-off as well.
At National, we used HSIM for full-chip top-level simulation of PLL
circuits and VCO loops. We did a comparison between HSIM and Star-Sim
on a PLL. Found that accuracy was comparable, simulation speed was
somewhat better for HSIM, but memory utilization was much smaller
(better) for HSIM than Star-Sim."
- Michael Fliesler of National Semiconductor
"I can speak to using Nassda, having been a EPIC TimeMill user before.
In the wacky world of very high speed mixed signal, we still find
ourselves flattening to the transistor level to verify functionality
and timing. This can occur in some mixed signal blocks where the
interface signals can not be registered. In those cases, Nassda HSIM
rules. It takes a little effort to learn to tune in the sims but not
bad and well worth it. We like HSIM's ability to mix Spectre and SPICE
format files and take LPE data in either raw SPICE or DSPF. It's
ability to control the simulation accuracy at the subcircuit level
is just the ticket. But in many cases you don't have to. It's like
dumping your laundry in without having to separate the colors :)
Besides, the Nassda people don't run duck and cover drills when they
hear mixed signal folks comming."
- Grego Sanguinetti of Accelerant Networks
"We have been a heavy user of Nassda's HSIM product and we feel that it
is great. Their recent run time improvement is even more impressive
when we utilize a hierarchical netlist. We have been able to simulate
the whole memory array without having to artifically, and manually,
create a 'critical path only' netlist. This has eliminated a lot of
possible human errors and thus improved the quality of our results."
- Raymond Leung of Virage Logic
"The reason we purchased HSIM from Nassda was because we are short on
time and needed a faster analog simulator. So far we are mixed on
our happiness. Some applications have worked out great and some have
left engineers frustrated and disappointed. I do have to say that
Nassda provides outstanding support on fixing problems. However, it
would be much better just to supply software that works as advertised.
Of course, not even Microsoft can come close to that. ;)"
- [ An Anon Engineer ]
"We also decided to purchase Nassda's HSIM. My belief is give our
engineers the best tools to get the job done on time. Engineers should
not be fighting with the tools. It may cost more than Nanosim or
StarSimXT, but from our Nassda benchmarks and from the positive comments
from the engineers, HSIM was well worth it."
- [ An Anon Engineer ]
"FTL Systems sells a simulator that can co-simulate SPICE, VHDL, VHDL
AMS, Verilog, Verilog AMS, and C++ all at the same time, and simulates
on up to 128 processors simultaneously. I think it makes coffee and
straightens up your desk, too. One of my people was very interested
in this tool.
Dolphin Integration from France sells SMASH, a simulator for SPICE,
VHDL, Verilog, VHDL-AMS, ABCD (behavioral analog) and C. They
emphasize it's a single engine for it all, not several engines
communicating through a backplane."
- John Weiland of Intrinsix
"SMASH from Dolphin is a very nice SPICE simulator. It allows the
abstraction of VHDL, Verilog, ABM, with SPICE elements and that makes
it very powerfull. The documentation of this tool is lacking however
so, getting things done when using the most powerfull features is
usually difficult and many times requires an email to Dolphin to answer
technical questions. I don't have much to say about this tool. It
just works and I like it.
PSpice (now owned by Cadence) for the most part, sucks. This tool has
been drug through the mud 10 times over and the last incarnation I
saw of it, it was just a mess. I do have to say that the tool was
pretty good about getting good spice results once everything was
running. But the designers were constantly making a mess of the
interface and I never saw the schematic entry tool work worth a crap.
Why can't schematic guys understand "HIERARCHY". They all design for
the board designer and forget about the IC designer. I can really
understand why the workstation based tools have been required for IC
design over the last 10 years. PSpice never figured it out in terms of
supporting hierarchy in the tool. Netlisting could take an hour in
some cases for a large memory design."
- David Ward of SemQuest, Inc.
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