[oxinabox]

A modern circuit simulator, that has a fully featured programable API, that can be run from a real modern programming language, would be a dream. Every simulator i have used has been pretty limited in that way, or at least those features were not well advertized. Even the insanely expensive ones. I mean the most expensive ones (like $100K liscense type deals, like Cadence) are if anything even less modern from a user interaction perspective.

My first academic paper (https://www.oxinabox.net/publications/White2015PsoTransistor...) was based on doing a search over parameters for the transistors being used in a circuit. The way that whole thing work was by string mangling the netlist file to update the parameters. Triggering the simulator on the commandline. Getting it to output a CSV of the signals. Parsing that CSV, and detecting edges and then measuring timing that way. Then throwing it at a particle swarm optimizer to fine a new one. That sucks from a user experience. It's a super cool way to solve problems though. that would be so easy with a real API.

Further, with julia being a differnetiable programming language, rather than having to use a particular swarm optimizer to search, I could have been differentiating it, and using some sophisticated gradient descent like LBGFS etc.

I hope that some of the general tools like this will be an outcome of this project.

[multiply]

A lot of semi companies have built their own simulation environments because the EDA vendor's provided tools are very limited in what they can do and difficult to use. Many users go to Python, Excel or MATLAB because the programming/math capabilities of the EDA tools are inadequate. Over time these home-grown environments become a burden and the developer disowns it and it becomes a headache.

The EDA tools have no ecosystem you can hook into and they don't really care about the user trying to put the simulators into a flow to solve their problem. It is a bunch of point tools each with their own embedded interpreter that don't play together. I sure hope there is a plan to create a better set of tools so I can write custom netlist checks and do something novel (like get derivatives out of the simulator) and in-memory (no slow disks) and run custom Julia checks during simulation. Julia is a much better match because running Python or MATLAB code within the simulator is way too slow. I'll keep watch for sure.

[stjohnswarts]

I had to leave a company over that. I had made a personal fpga construct generator for various easily parameterizable modules. It worked pretty well but it was a mess and needed to be redone pretty badly, but it was good enough. I shared it upon request with a couple of engineers and before I knew it there were probably 25 EEs using it. They wanted "more" and I told them it was a personal tool and they were more than welcome to extend it. This actually angered a few of them and they "reported" me another manager a couple levels higher. He told me that I had to maintain/extend it and to use as much time as it took. (I was a junior engineer at the time). I told him I was there to be an electrical engineer and not a legacy code maintainer. He gave me an ultimatum and being a person that doesn't like ultimatums, I told him I resigned on the spot. I gathered the few items I had on my desktop waved at a couple buddies and went on out the door. I never regretted that decision. Moral (I guess?) be careful of what you share :) .

[toomuchtodo]

If they didn't lay claim to the IP, you should polish it and offer it for sale, or use it as interview material at someplace developing similar technology.

[dr_zoidberg]

First and foremost: I AM NOT A LAWYER.

With that out of the way...

They could argue that since it was a tool that was made to help with his job at at the company, then it's internally developed. If there are no clear grounds or easily presentable evidence (even if there was!), he's out in the wild with a liability.

The only place where I can see him in the clear is if they had a repo going back to before the work on the company and they could prove the tool was a personal project, and unrelated to the job. Even then, Company could still sue and burden them with legal fees/process until they tire him out and BINGO, now they own their IP.

The alternative could be starting a new project, completely open source from the start (probably with one of the more liberal licenses) and get crowdfunding to develop and maintain it. Assuming they are interested in doing that, of course.

[posterboy]

Betcha it's Xilinx today, or a branch of Analog, or something like that. You get the idea.

[stjohnswarts]

Oh the creation of modules has gotten much better with languages like SystemVerilog and SystemC :) . What I did was a very rudimentary effort in perl (later ported it to python). Kind of like people look like "excel gods" at some company when they take some mundane manual tasks and do some excel scripting and take a 3 day job down to 15 minutes. I just happened to be the only EE with the soul of a coder while I was there. I was under very heavy NDA at the time, I'm sure others were doing the same at their companies. tldr; it wasn't anything special and is much more common these days. Basically it eliminated a ton of copy-pasta and manual editing.

[seanmclo]

I can attest first-hand to the "headache" that comes from semi company simulation environments. Not only are they horribly outdated (in Perl/Tcl), but they're different at every company you work at. There's no gold standard because the standard that these EDA companies ought to be making doesn't exist.

There needs to be an open initiative between semi companies to create a standard simulation environment -- with compilers, unit-test frameworks, and all sorts of simulation (gate-level, analog/mixed signal, emulation, etc). Hell, just give me a free IDE plugin for SystemVerilog that actually works.

This lack of a standard seems to me like the critical path in hardware design. I'm trying to support projects to fix this like SVLS (A language server for SystemVerilog: https://github.com/dalance/svls) but these are all hard problems to solve. This industry is relatively niche and doesn't seem to have many engineers interested in FOSS.

[built_with_flux]

Shameless plug: We are building this over at flux.ai

its early days but you can start playing with our beta

[kayson]

It's an absolute nightmare. Cadence added support for Matlab calculations on simulator outputs, but its clunky and inconsistent. Don't even get me started on how long it takes to do basic calculations on numbers that should already be in memory...

[multiply]

My worst experience was doing a simple min/max of each signal took 7x longer than the simulation. I'd be so happy to toss TCL in the trash. I spent a long time debugging because TCL expr doesn't do -2^2 correctly. The error messages don't tell you the line number and I found no good way to debug. Things like that are just the tip of the iceberg of time wasted fighting with arcane tools. I suppose others have their own stories.

[kbr2000]

In Tcl's expr:

^ stands for bitwise XOR: so [expr {-2^2}] results in -4

* stands for exponentiation: so [expr {-2*2}] results in 4

Both seem correct to me, taking into account how integers are represented in binary (two's complement for the negative ones).

With regards to debugging dynamic programming languages, it is different as compared to their static counterparts, since much is delayed to happen at runtime (as opposed to at compilation time). But it also opens up possibilities (like introspection, ability to intervene in the scripts while they run, ...). It requires a different mindset.

[blacksqr]

I've always been astounded that much of the rage against Tcl seems to stem from the fact that it works as documented, rather than according to the rules of other languages.

[kbr2000]

Mmmn, HN stripped out the half of the double asterisks, now I made it confusing myself... Too late to edit my comment above, but it needs to be like this:

** stands for exponentiation: so [expr {-2**2}] results in 4

[KenoFischer]

We are building something along these lines that the DARPA work sits on top of, so if you have a current need, do feel free to reach out (email is in profile).

[ur-whale]

Talking about this - sorry for the slight OT - I really wish Linear would consider OpenSourcing LTSpice.

I mean ... it's a really nice tool, they are giving away from free anyways ... if they OpenSourced it, the kind of feature you describe here (and which I've been sorely missing as well) would be a no-brainer to implement.

Not to mention all the other enhancements the community could and would bring to it.

[jacquesm]

That is an interesting optimization trick, essentially a brute force search over a parameter space in order to minimize silicon area, I am assuming this was for cells that were going to be replicated many times on the same die?

[oxinabox]

Something like that is the idea. Silicon area is what costs money. Use as little as possible while still being fast enough to beat the clock-rate of your system. PSO's are way better than brute force. but yeah.

It was a purely academic work for a masters level CS unit. I had just finished a masters level electrical engineering unit on silicon circuit design. Where the final project was to design an adder that minimized silicon used (and thus cost) while also being faster enough. And the hard bit is that you want big thick doped regions for high conductivity, but also the bigger the area the more paracidic capacitance. And so there are some tricks the to find good sizes, like progressive sizing and stuff. But afaik there is no actual answer, at least not one we ever learned. So a lot of trial and error went into it. It was a hard project.

And so then I did this CS unit where the project was "Do something interesting with a particle swarm optimizer". And i was like "lets solve this". and once I saw the results, i was like "this is actually really good", and so the lecturer and I wrote a paper about it.

It is a real problem. Minimizing silicon area subject to speed. I bet the big integrated designers have there own tricks for it that i don't know about. To do it really well you need to miminal the real area so also need to solve layout (which is a cool cutting and packing problem). (and ther are also nth order effects, like running traces over things can cause slow downs, because electromagnetism reasons) I bet a bunch of folk on HN know this problem much better than i do though. probably something bad in my solution, but i think it illustrates the utility

[kayson]

Very cool paper. Your observations in V.B.4 are pretty well understood in circuit design. If you've not heard of it, you might be interested in https://en.wikipedia.org/wiki/Logical_effort. Turns out the optimum scaling for propagation delay is e (natural log constant), but I don't know if I ever learned anything about the optimum for area.

Now that everyone is using finfet processes, the layout part is pretty easy to solve because transistor widths have to be a certain number of fins and the layout is extremely regular.

One thing your analysis didn't include, which actually ends up being quite significant, is the extra capacitance caused by the wires between transistors. This changes the sizing requirements substantially.

I've done some custom logic cell design, and I always had to use a lot of trial and error, though generally I was concerned more with speed than area. I'm not sure exactly what the development process is at my current employer, but it seems like its a lot of manual work. I'm guessing they set area targets based on experience and attempt to maximize speed where possible.

Ultimately, everything gets placed and routed by a computer anyways!

[oxinabox]

> Your observations in V.B.4 are pretty well understood in circuit design.

Indeed, I am actually surprised the paper doesn't include something like _"This is inline with the well known result for progressive sizing [cites textbook]"_. It was my first paper, i was worse at writing things then. :-D

> One thing your analysis didn't include, which actually ends up being quite significant, is the extra capacitance caused by the wires between transistors. This changes the sizing requirements substantially.

Good point. And not easy to model in a SPICE style simulator. I guess one could maybe introduce explict capacitors and them compute capacitiances by making some assimptions about layout.

[kayson]

> I guess one could maybe introduce explict capacitors and them compute capacitiances by making some assimptions about layout.

That is, in fact, exactly what we do! I think it would be pretty straight forward for your large buffer example - you can model it as a fixed capacitance at each output which corresponds to the routing between inverters, which would be the same for all sizes, plus some scaling capacitance that relates to the size of the transistor itself, which you already have.

The adder would be trickier, for sure. Regardless, in my experience, just adding a reasonable estimate is good enough to get you close in terms of sizing in schematics, then you fine tune the layout.

[jacquesm]

Thank you for writing it up and posting it here, one of the more interesting comment threads.

[throwaway9870]

There was a simulator called HSIM that I used 20 years ago to do what you describe. It had a C api that I integrated with. It was more of a fast Spice rather than equivalent to HSPICE or Spectre. I coupled it with a little mini-language I wrote to do easily scriptable regression tests for our system. I believe Synopsys bought the company.

[eternauta3k]

Have you looked into Spectre's interactive mode? You can send SKILL commands to change parameters and rerun simulations. It's not documented, though.