A First, Complicated Project at Circuit Design with NG-SPICE

One subject which I wrote about in an earlier posting, was that software exists by the name of ‘SPICE’, which stands for “Simulation Program with Integrated Circuit Emphasis”. There are several variants of this software in existence, but the version which I am focusing on for now is the Open-Source ‘NG-SPICE’ system, which needs to be bundled with numerous other packages under Linux, really to be useful. One important package is ‘ngspice-doc’, but there is a whole suite of Linux packages referred to as ‘gEDA’.

Simply having tested a few demo-projects, is not the same thing as actually having designed a circuit, and having witnessed that project ‘work’, at least according to the simulation. Just last night, I did the latter, in order to get a better, working grasp of how to use the software, and also, some idea of the sort of error messages and problems which invariably occur on a first-time basis. What this means is that I actually designed a circuit using the ‘gEDA Schemtic Editor’, which is also known as ‘gschem’, and then ran multiple simulations of the circuit, discovering at first that it had performance issues as I had imagined it, modifying it numerous times, and ending up with a version of the circuit, which I could be satisfied with for now.

The circuit which I was designing, actually involved MOSFETs, because those are the most important components in circuit-design today, and surely enough, I did run into initial problems. One of the tasks which we must complete, when using active components in SPICE, is to define the component, which is as fundamental as the fact that we also don’t just put a resistor, but must also specify what the Value of the resistor is in Ohms. Well with active components, we must do something similar, which also goes under the GUI heading of the Value attribute for the component. Therefore, MOSFETs, be they NMOS or PMOS, also have values, and by default, those values are defined by a Model Card, from which the computer can predict such physical properties about the NMOS or the PMOS transistor, as what its gate-capacitance is, how well it conducts when switched to conductive, conversely when the gate-voltage is zero, etc., etc., etc..

But, because NG-SPICE (v26) is advanced software – though still not the latest version – it may not require that the user defined all these parameters each time he or she considers designing a circuit, because standard component specifications exist.

By default, our MOSFETs have Reference Descriptors that begin with the letter “M”, and not with the letter “Q”, which would stand for a Bipolar Transistor, but which the GUI of ‘gschem’ suggests for the user when he first clicks a MOSFET into his circuit. So we override that, by editing the RefDes into a text-string that has the letter “M” followed without spaces by a number.

What I next proceeded to do, was to put MOSFET-transistors into my circuit, which from the GUI, only had 3 pins. This is a common way in which MOSFETs are often diagrammed, and looked something like this:

diffamp_l

Believing that I could just accept what the GUI had constructed, I next tried to simulate the circuit, and received the error, which roughly stated “Unable to find Definition of Model.” This error-message wasted much of my time trying to solve, because I had in fact created a Model Card for the transistors which I was going to use, and at first, I despaired that NG-SPICE might not be as good as paid-for software. But I soon learned that indeed, the following example is a sufficient Model Card for an arbitrary NMOS transistor, with which circuits can be designed:

http://dirkmittler.homeip.net/text/NMOS1.mod.txt

Similarly, we can conjure a default PMOS transistor like so:

http://dirkmittler.homeip.net/text/PMOS1.mod.txt

In actual circuit-design, we’d drop the .TXT Filename-Extension, that makes the above examples readable in a Web-browser. Not only that, but we can also use the ‘gschem’ GUI, to embed such definitions directly into the Netlist, by giving them as a ‘Model’ attribute. So what was causing this error message, in my example? The fact is that MOSFETs are 4-pin components by nature. They have a hypothetical Source, a hypothetical Drain, a Substrate Electrode, and a Gate. It’s the voltage between the Gate and the Substrate Electrode, that finally determines how conductive the MOSFET is to become. By convention, many practical MOSFET-packages tie the Substrate Electrode together with the Source lead, which also happens to make the Source different from the Drain.

nmos_3_2

By telling NG-SPICE that we’re including a ‘MOSFET_TRANSISTOR‘ in our circuit, we’re telling this program to read 4 Nodes from the Netlist, to parse what the transistor is to be connected to. But, when the GUI only provides 3 arguments, an error ensues, that garbles the attempt of NG-SPICE to parse the Netlist. That’s all. Curiously, the reverse error does not happen. If I conjure a 4-lead MOSFET-symbol from the GUI, but specify a 3-lead MOSFET (more on that below), then I obtain a well-managed error message, that tells me what the problem is.

(Updated 06/14/2018 … )

Actually, the symbols above are also different in another way. In theory, one stands for an enhancement-mode, and the other, for a depletion-mode transistor. But, because under Linux, ‘this software is divided into two departments’, effectively, this does not matter.

The GUI allows schematics to be drawn in such a way, that Netlists result, while the actual NG-SPICE software emulates what these Netlists define. It’s in the emulation of the Netlists, that the decision is also made, as to whether a component is an enhancement-mode or a depletion-mode, or a subcircuit component… ( :1 )

(Updated 06/16/2018 : )

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The failings of low-end consumer software, to typeset Math as (HTML) MathML.

One of the features which HTML5 has, and which many Web-browsers support, is the ability to typeset Mathematical formulae, which is known as ‘MathML’. Actually, MathML is an extension of XML, which also happens to be supported when inserted into HTML.

The “WiKiPedia” uses some such solution, partially because they need their formulae to look as sharp as possible at any resolution, but also, because they’d only have so much capacity, to store many, many image-files. In fact, the WiKiPedia uses a number of lossless techniques, to store sharp images as well as formulae. ( :1 )

But from a personal perspective, I’d appreciate a GUI, which allows me to export MathML. It’s fine to learn the syntax and code the HTML by hand, but in my life, the number of syntax-variations I’d need to invest to learn, would be almost as great, as the total number of software-packages I have installed, since each software-package, potentially uses yet-another syntax.

What I find however, is that if our software is open-source, very little of it will actually export to MathML. It would be very nice if we could get our Linux-based LaTeX engines, to export to this format, in a way that specifically preserves Math well. But what I find is, even though I posses a powerful GUI to help me manage various LaTeX renderings, that GUI being named “Kile”, that GUI relies back on a simple command-line tool named ‘latex2html’. Whatever that command-line outputs, that’s what all of Kile will output, if we tell it to render LaTeX specifically to HTML. ‘latex2html’ in turn, depends on ‘netpbm’, which counts as very old, legacy software.

One reason ‘latex2html’ will fail us, is the fact that in general, its intent is to render LaTeX, but not Math in any specific way. And so, just to posses the .TEX Files, will not guarantee a Linux user, that his resulting HTML will be stellar. ‘latex2html’ will generally output PNG Images, and will embed those images in the HTML File, on the premise that aside from the rasterization, PNG Format is lossless. Further, if the LaTeX code was generated by “wxMaxima”, using its ‘pdfLaTeX’ export format, we end up with incorrectly-aligned syntax, just because that dialect of LaTeX has been optimized by wxMaxima, for use in generating .PDF Files next.

(Updated 05/27/2018 : )

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I’ve just custom-compiled ‘Aqsis’.

To give some context to this proclamation, I had written an earlier posting, about adapting the non-packaged software named ‘Ayam‘ to Debian / Stretch, that had worked just fine under Debian / Jessie. This is a GUI which constructs complex ‘Renderman‘-Compliant rendering instructions, in this case in the form of .RIB-Files, which in turn, ‘Aqsis’ can turn into 2D perspective views of 3D scenes, that have been software-rendered. OTOH, Ayam itself uses OpenGL and H/W rendering, for its GUI.

What I had found before, was that Ayam did not seem stable anymore under Debian / Stretch. I apologize for this assessment. Under close scrutiny, my computer has revealed, that it was really Aqsis giving the problems, not Ayam. Aqsis is a text-based tool in effect.

Ayam does not specifically need to be used with Aqsis to do its rendering. It can be set up to use other rendering-engines, most of which are quite expensive. Aqsis just happens to be the best Open-Source rendering-engine, whose language Ayam speaks. And at this point I’d say that Ayam is still quite stable, after all, under Debian / Stretch.

As is often the case with such troubles, I next sought to custom-compile Aqsis, to see whether doing so could get rid of its quirks. What were its quirks?

Finally, the only problem with Aqsis was and remains, that it cannot produce a real-time preview of the scene being edited, which it used to provide using a component-program named ‘piqsl’. And the reason why the packaged version of Aqsis does not have ‘piqsl’ under Debian / Stretch, is because this distribution of Linux has a very new ‘Boost’ library ( v1.62 ) , and the visual component to Aqsis, that could produce a display, still relies on the Qt4 libraries and their API, which have begun to bit-rot. The Qt4-specific code of Aqsis cannot parse the newest usage of the Boost libraries, and Debian maintainers have long since discovered this. They are shunning the use of ‘libqt4-dev’ and of ‘libqt4-opengl-dev’ to build any of their packages. So they were effectively forced to package a version of Aqsis, which was missing some important components.

(Updated 12/12/2017 … )

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Atomic Game Engine Installed – twice

One of the projects which I have recently undertaken, is to compile and install Atomic Game Engine, both on my Linux laptop ‘Klystron’, and on my Windows 7 machine ‘Mithral’. This was originally a closed platform, but has received renewed interest, because it is now available under the MIT license, which is a form of Open-Source licensing, more permissive than GPL v3 is.

This platform has the eventual capability, to deploy 3D applications and games, to Windows, OS/X, Linux, Android, iOS and WebGL recipient-platforms, while some forms of it will run under Windows and Linux, in my own experience.

I have to say though, that my ability to get the Linux version of this game-design platform working, was not due to my own prowess, but rather to the fact that the development team at Atomic Game Engine, provided dedicated and consistent technical support to me, every time I ran into a problem. I would guess they are rather tired of answering my many questions for the moment, so it is also good news, that both under Linux and Windows, my installations of this platform are complete – to my own satisfaction.

I have exported a 3D application to Android from my Windows platform, but have not reproduced this success under Linux, mainly because the platform requires that I specify where my Android SDK and where my Ant executable are located – sensibly – and I do not have any Android SDK presently, installed on ‘Klystron’. I do have the Android SDK installed on ‘Mithral’, which as I said is required, and so the export to Android worked there.

Installation under Windows was much more straightforward than it was under Linux, which is often the case, because the Windows version comes as an available binary SDK, while under Linux it still needs to be custom-compiled. And whenever we custom-compile anything, we can run into dependency issues.

One major issue I faced under Linux, was the fact that the Mono packages that are standard for my Debian distribution, are not adequate in what they provide, for development in C# to be enabled. And so what I needed to do, was to subscribe to another Mono repository, managed by Mono project, to upgrade my whole Mono installation, and after that, C# also worked.

So, Atomic Game Engine allows for 3D applications and games to be designed, using the languages C#, JavaScript, and TypeScript, according to my own experience… But, a C# Project cannot be exported for WebGL playing.

Also, I have discovered along the way, that We are no longer expected to install ‘Visual Studio 2015 Express’, but rather “Visual Studio 2015 Community Edition”, and in order to get C# support to work properly on my Windows 7 machine, I needed to do an in-place upgrade, from ‘VS Express’ to ‘VS Community’.

I am pleased that all the installation and upgrading seems to have gone well, and seems to have left me with no major reliability issues, either on ‘Klystron’ or on ‘Mithral’.

However, because the build of Mono now on ‘Klystron’ is non-standard, I cannot vouch for it in general. On my actual server-box ‘Phoenix’, I must choose to stick with the more conservative Mono packages, that are meant to go with Debian, because this box needs to run reliably 100% of the time. OTOH, on ‘Klystron’, I had nothing else depending on Mono, for which reason I was also willing to do the upgrade.

Dirk