Issie - an Interactive Schematic Simulator with Integrated Editor

Issie (Interactive Schematic Simulator with Integrated 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. Issie is developed and actively used in teaching at Imperial College London.

• If you are just interested in using the application, jump to the Getting Started section.
• If you want user documentation and news go to the web pages.

For more technical 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 5 is the module bundler responsible for the JavaScript concatenation and automated building process: the electron-webpack build is automated using the pre-existing scripts under the scripts directory.

The drawing capabilities are provided (now) by a custom schemetic editor library implemented in F# and specialised for digital 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": {
    "clean-dev-mac": "sudo killall -9 node && sudo killall -9 dotnet && sudo killall -9 issie",
    "clean-dev-win": "taskkill /f /im node.exe && taskkill /f /im dotnet.exe && taskkill /f /im issie.exe",
    "compile": "dotnet fable src/Main -s && dotnet fable src/Renderer -s",
    "dev": "dotnet fable watch src/Main -s --run npm run devrenderer",
    "devrenderer": "dotnet fable watch src/Renderer -s --define ASSERTS --run npm run start",
    "start": "cross-env NODE_ENV=development node scripts/start.js",
    "build": "cross-env NODE_ENV=production node scripts/build.js",
    "pack": "npm run compile && npm run build && electron-builder --dir",
    "dist": "npm run compile && npm run build && electron-builder",
    "buildonly": "electron-builder",
    "compile-sass": "cd src/renderer/scss && node-sass main.scss main.css"
  }

Defines the in-project shortcut commands as a set of <key> : <value lines, so that when we use npm run <stript_key> it is equivalent to calling <script_value>. For example, in the root of the project, running in the terminal npm run dev is equivalent to the command line:

dotnet fable watch src/Main -s --run npm run devrenderer

This runs fable 3 to transpile the main process, then (--run is an option of fable to run another command) runs script devrenderer to transpile to javascript and watch the F# files in the renderer process. After the renderer transpilation is finished start.js script will be run. This invokes webpack to pack and lauch the javascript code, under electron, and also watches for changes in the javascript code, and hot loads these on the running application

As result of this, at any time saving an edited F# renderer project file causes (nearly) immediate:

• fable transpile to from F# to javascript file (dependent F# files may also be transpiled)
• webpack hot load of any changed javascript files to the running electron application

The build system depends on a Fake file build.fsx. Fake is a DSL written in F# that is specialised to automate build tasks. Build.fsx has targets representing build tasks, and normally these are run via build.cmd or build.sh, instead of using dotnet fake directly:

• build <target> ==> dotnet fake build -t <target>

Code Overview

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 (in )

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.

The compile process is controlled by the .fsproj files (defining the F# source) and webpack.additions.main.js, webpack.additions.renderer.js which define 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 or file	Description
Main/main.fs	Code for the main electron process that sets everything up - not normally changed
Renderer/Common/*	Provides some common types and utilities, as well as interfaces to libraries APIs and custom libraries
Renderer/Interface/*	Contains low-level interface functions, and all the low-level file management
Renderer/DrawBlock/*	Contains all the SVG-based schematic editor code in F#
Renderer/Simulator/*	Contains the logic to analyse and simulate a schematic sheet
Renderer/UI/*	Contains the UI logic
./renderer.fs	Top-level file that drives the renderer code: contains Elmish MVU loop and Electron menu code

Tests folder

Currently tests are very old, and will not work. They are based on F# Expecto testing library and in principle the widthinferrer and simulator code (which runs under dotnet) could be tested here.

Static folder

Contains static files used in the application.

Docs folder

Contains source information that controls the project documentation web site https://tomcl.github.io/issie/.

Project versus File in the Issie application

Issie allows the users to create projects and files within those projects. A Issie project is simply a folder named <project-name> that contains an empty file named <project_name>.dprj (dprj stands for diagram project). The project folder any non-zero number of design files, each named <component_name>.dgm (dgm stands for diagram). each deisgn file represents one design sheet of a hierarchical hardware design, sheets can contain, as components, other sheets.

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

Build Overview

This project uses modern F# / dotnet cross-platform build. The build process does not normally concern a developer, but here is an overview for if it needs to be adjusted. Details are included below under Getting Started As A Developer.

• Before anything can be built Dotnet & Node.js are manually be (globally) installed. Dotnet includes the paket tool which will manage other dotnet-related dependencies. Node.js includes npm which will do the same for Node-related dependencies. NB - there are other popular packet managers for Node, e.g. Yarn. They do not mix well with npm, so make sure you do not use them. Confusingly, they will sort-of work, but cause occasional install incompatibilities.
  • Dotnet dependencies are executable programs or libraries that run under dotnet and are written in C#. F#, etc.
  • Node dependencies are (always) Javascript modules which run under Node.
• Initially (the first time build.cmd is run) the build tools categorised in dotnet-tools.json are installed by dotnet tool restore.
  • fake (F# build automation tool)
  • fable (F# to js compiler)
  • paket (alt dotnet package manager to Nuget)
• Next all the project Dotnet dependencies (paket.dependencies for the whole project, selected from by the paket.references in each project directory, are loaded by the paket packet manager.
• Finally fake runs build.fsx (this is platform-independent) which uses npm to install all the node (Javascript) dependencies listed in package.json. That includes tools like webpack and electron, which run under node, as well as the node libraries that will be used by needed by the running electron app, including electron itself. These are all loaded by the npm packet manager.

Getting Started

If you just want to run the app go to the releases page and download and run the latest prebuilt binary for your platform (Windows or Macos). Issie will require in total about 200M of disk space.

• Windows: unzip *.zip anywhere and double-click the top-level Issie.exe application in the unzipped files.
• Macos: Double click the dmg file and run the application inside the folder, or drag and drop this to install.
  • The binaries are not signed. You will need to perform a one-off security bypass.

Issie installs and runs without making system changes - all of its code is inside the directory you download. You can delete this and replace it by a later version of Issie. Each design sheet is stored in a similarly named file under the porject directory. The subdirectory backup there contains a large numbers of backup snapshots for design recovery. These are not needed for Issie operation so you can delete them - or even the whole backup directory, if you wish.

Getting Started as Developer

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

Development Install Prerequisites (common to windows, macos, linux)

Download and install (if you already have these tools installed just check the version constraints).

• .Net 6 SDK. Version >= 6.0, < 7
• Node.js v16. v16 LTS - NOT latest 18
  • Node.js includes the npm package manager, so this does not need to be installed separately.
  • If you are using a different version of Node for developmnet on other projects, global install (the default) may interfere with this. You will need to do a more complex local node install.
• (recommended) Visual Studio 2022 which includes F# 6.0, Install with:
  • Workload: .Net Desktop development
  • Ticked: F# language support
• (recommended) install hyper.js or (better on Windows is Windows Terminal.

Issie Development

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

2. Navigate to the project root directory (which contains this README) in a command-line interpreter, or start one from directory context menu.

3. Run build.cmd under Windows or build.sh under linux or macos. This will download and install all dependencies then launch the application in dev mode 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 whole application again run npm run dev. (NB npm run fastdev is the same with debugging switched off to increase simulation speed a lot).
• To generate distributable binaries for dev host system npm run dist.
• If you have changed packet.json and therefore need to remake the lock file paket-lock.json use npm install.
• On windows build killzombies will terminate orphan node and dotnet processes which occasionally happen using this build chain after unusual terminations

NB - in parallel with the above compilation, Issie code will always compile without errors (but not run)under dotnet. Compilation should be identical but when unsure why there is an error it is very helpful to build the current code under VS or VSC and get easier to find error messages. Similarly, VS or VSC can be used with confidence to refactor code, testing with compilation. Building under VS or VSC cannot work because the code depends on electron and Node APIs to work.

Node management details

• package-lock.json contains exact package versions and is downloaded from the repo. Normally you don't need to change this. The standard build above will run npm ci which checks and audits packages but does not change the lock file.
• If you need to add upgrade a package (in package.json1) use npm install to recreate a lock file, which can be pushed to the repo.
• Single packages can conveniently be changed or added using npm upgrade name or npm [-D] install name instead of editing package.json.
• If a package audits with a problem use npm ls name to find which of the required packages use it (usually upgrading or replacing them will remove the problem).

Development on Macos

A clean build will work equally well on macos, however things are more likely to go wrong if you have previously installed conflicting packages:

• Legacy versions of dotnet - can if needed be removed as here:

  curl -O https://raw.githubusercontent.com/dotnet/sdk/main/scripts/obtain/uninstall/dotnet-uninstall-pkgs.sh
  chmod u+x dotnet-uninstall-pkgs.sh
  sudo ./dotnet-uninstall-pkgs.sh
  

• Root permissions in dev files. For dev to work smoothly you need every configuration file to be installed under your own username, so you have r/w access. This will break if you ever find yourself using sudo to root install software, or if you have done this some time in the past. In that case you can temporarily get round issues by using sudo to run the development (or the generated app) with admin privileges. This is the wrong thing to do. Instead you should use
  • chown -R `whoami` dir for each directory that might have the files with bad permissions. Typically your dev directory . and /usr/local.
• Uninstalling and reinstalling latest dotnet is helpful if dotnet has been installed wrong.

Under the hood for developers

Although the dev chain is complex, it is now very smooth and identical for all platforms. Each of these steps can be performed as needed:

1. You need Dotnet SDK and Node installed. Dotnet SDK gives you F#.
2. dotnet tool restore gets you the dev tools: Fable compiler, Fake build automation, paket dotnet package manager. (Node package management is via npm which comes with Node).
3. dotnet paket install installs all of the dotnet-side packages needed
4. npm ci downloads and audits correct versions of all of the npm packages. npm install will redo the versions if these have changed and generate an updated lock file.
5. npm run dev, npm run dist, npm run devfast: scripts defined in package.json which control developmment (with HMR) or production compilation with Fable, and packing using Webpack 5.
6. The build.cmd and build.sh scripts package the above steps adding some not usually necessary directory cleaning - you can run them individually in order if you have problems.

• To update the tool versions (not normally needed) edit dotnet-tools.json.
• To change the dotnet packages used (advanced) change paket.dependencies at top level and paket.references in the directory of the relevant .fsproj file. Currently dotnet packages are not pinned to versions so latest compatible versions are always used. This is probably wrong but seems to work well.
• To interface to a new Node package from F# see the excellent Fable documentation. The best way to do this is to write an F# interface file which provides static typing (like a typescript definition file). In fact there is a wonderful automatic converter ts2fable which generates F# interfaces from typescript .d files. This works well, but manual adjutsment is needed for anything complex. See the Electon API interface in Issie which was generated in this way from a published electron API .d files - in that case the manual adjustment was quite unpleasant because Electron API is very complex.
• To understand Elmish and MVU read the excellent Elmish book
• For more documentation on Issie in addition to XML code comments see the Issie Wiki

Reinstalling Compiler and Libraries

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

Creating binaries

npm run dist will generate the correct binaries for your system under /dist.