Issie - an Integrated Schematic Simulator with Interactive Editor

Issie (Integrated Schematic Simulator with Interactive Editor) is an application for digital circuit design and simulation. It is targeted at students and hobbyists that want to get a grasp of Digital Electronics concepts in a simple and fun way. Issie is designed to be beginner-friendly and guide the users toward their goals via clear error messages and visual clues.

The application is was initially developed by Marco Selvatici, as a Final Year Project.

It is currently being maintained by Tom Clarke (owner) and Edoardo Santi (Summer UROP).

If you are just interested in using the application, jump to the Getting Started section. For more info about the project, read on.

This documentation is partly based on the excellent VisUAL2 documentation, given the similarity in the technology stack used.

Introduction

For the Issie website go here.

The application is mostly written in F#, which gets transpiled to JavaScript via the fable compiler. Electron is then used to convert the developed web-app to a cross-platform application. Electron provides access to platform-level APIs (such as access to the file system) which would not be available to vanilla browser web-apps.

Webpack 4 is the module bundler responsible for the JavaScript concatenation and automated building process.

The drawing capabilities are provided by the draw2d JavaScript library, which has been extended to support digital electronics components.

The choice of F# as main programming language for the app has been dictated by a few factors:

• the success of the VisUAL2, which uses a similar technology stack;
• strongly typed functional code tends to be easy to maintain and test, as the type-checker massively helps you;
• Imperial College EEE/EIE students learn such language in the 3rd year High-Level-Programming course, hence can maintain the app in the future;
• F# can be used with the powerful Elmish framework to develop User Interfaces in a Functional Reactive Programming fashion.

Project Structure

Electron bundles Chromium (View) and node.js (Engine), therefore as in every node.js project, the package.json file specifies the (Node) module dependencies.

• dependencies: node libraries that the executable code (and development code) needs
• dev-dependencies: node libraries only needed by development tools

Additionally, the section "scripts":

{
    ...
    "scripts": {
    "compile": "electron-webpack",
    "dev": "electron-webpack dev",
    "dist": "yarn compile && electron-builder"
    },
    ...
}

Defines the in-project shortcut commands, therefore when we use yarn <stript_key> is equivalent to calling <script_value>. For example, in the root of the project, running in the terminal yarn launch is equivalent to running electron ..

The build system depends on a Fake file build.fsx. This has targets representing build tasks, and normally these are used, accessed via build.cmd or build.sh, instead of using yarn directly.

Code Structure

The source code consists of two distinct sections transpiled separately to Javascript to make a complete Electron application.

• The electron main process runs the Electron parent process under the desktop native OS, it starts the app process and provides desktop access services to it.
• The electron client (app) process runs under Chromium in a simulated browser environment (isolated from the native OS).

Electron thus allows code written for a browser (HTML + CSS + JavaScript) to be run as a desktop app with the additional capability of desktop filesystem access via communication between the two processes.

Both processes run Javascript under Node.

The src/Main/Main.fs source configures electron start-up and is boilerplate. It is transpiled to the root project directory so it can be automatically picked up by Electron.

The remaining app code is arranged in five different sections, each being a separate F# project. This separation allows all the non-web-based code (which can equally be run and tested under .Net) to be run and tested under F# directly in addition to being transpiled and run under Electron.

The project relies on the draw2d JavaScript library, which is extended to support digital electronics components. The extensions are in the app/public/lib/draw2d_extensions folder and are loaded by the index.html file. The index.html file is otherwise empty as the UI elements are dynamically generated with React, thanks to the F# Elmish library.

The code that turns the F# project source into renderer.js is the FABLE compiler followed by the Node Webpack bundler that combines multiple Javascript files into a single renderer.js. Note that the FABLE compiler is distributed as a node package so gets set up automatically with other Node components.

The compile process is controlled by the .fsproj files (defining the F# source) and webpack.config.js which defines how Webpack combines F# outputs for both electron main and electron app processes and where the executable code is put. This is boilerplate which you do not need to change; normally the F# project files are all that needs to be modified.

File Structure

src folder

Subfolder	Description
main/	Code for the main electron process that sets everything up - not normally changed
Common/	Provides some common types and utilities used by all other sections
WidthInferer/	Contains the logic to infer the width of all connections in a diagram and report possible errors.
Simulator/	Contains the logic to analyse and simulate a diagram.
Renderer/	Contains the UI logic, the wrapper to the JavaScript drawing library and a set of utility function to write/read/parse diagram files. This amd main are the only projects that cannot run under .Net, as they contain JavaScript related functionalities.

Tests folder

Contains numerous tests for the WidthInferer and Simulator. Based on F# Expecto testing library.

static folder

Contains static files used in the application.

docsrc folder

Contains source information copied (or compiled) into the docs directory that controls the project Github Pages website, with url https://tomcl.github.io/issie/.

Concept of Project and File in Issie

ISSIE allows the users to create projects and files within those projects. A ISSIE project is simply a folder named <project_name>.dprj (dprj stands for diagram project). A project contains a collection of designs, each named <component_name>.dgm (dgm stands for diagram).

When opening a project, ISSIE will search the given repository for .dgm files, parse their content, and allow the user to open them in ISSIE or use them as components in other designs.

Getting Started

If you just want to run the app go to the releases page and follow the instructions on how to download and run the prebuilt binaries.

If you want to get started as a developer, follow these steps:

1. Download and install the latest (3.x) Dotnet Core SDK.
   For Mac and Linux users, download and install Mono from official website (the version from brew is incomplete, may lead to MSB error later).

2. Download & unzip the Issie repo, or if contributing clone it locally, or fork it on github and then clone it locally.

3. Navigate to the project root directory (which contains this README) in a command-line interpreter. For Windows usage make sure if possible for convenience that you have a tabbed command-line interpreter that can be started direct from file explorer within a specific directory (by right-clicking on the explorer directory view). That makes things a lot more pleasant. The new Windows Terminal works well.

4. Run build.cmd under Windows or build.sh under linux or macos. This will download all dependencies and create auto-documentation and binaries, then launch the application with HMR.

• HMR: the application will automatically recompile and update while running if you save updated source files
• To initialise and reload: File -> reload page
• To exit: after you exit the application the auto-compile script will terminate after about 15s
• To recompile the application yarn dev
• To generate distributable binaries for dev host system yarn dist.
• if you have chnaged node modules use yarn package manager not npn, as in yarn install.

Reinstalling Compiler and Libraries

To reinstall the build environment (without changing project code) rerun build.cmd (Windows) or build.sh (Linux and MacOS).