Logic Paint

Inspired by Zachtronic's KOHCTPYKTOP, Logic Paint allows you to edit and simulate transistors, at scale.

A 16-bit micro-coded CPU I built based in Logic Paint, on the LC-3B micro-architecture.

2024 - Under Construction 🚧

We are moving to the web like it's 1999 😎

This project was originally designed to run as a vscode extension. Since then, vscode has made breaking changes. Also vscode extensions were never what I really wanted from this project. I'm currently in the middle of moving the whole thing over to a web interface, where you can explore other people's designs without needing an account, and make your own designs by logging in. I also have some exciting plans to support user-created plugins!

Standard Controls

The camera can be panned at any time (including while actively painting) by holding down the Space key. It can be zoomed at any time with the scroll wheel.

Standard controls like Ctrl+Z and Ctrl+S to undo and save should work just fine.

Modal Editing

Logic Paint is modal, the active mode is displayed in the upper left corner of the editor window. It has 4 primary modes:

• Visual (the starting mode) lets you select, copy, paste and delete cells.
• Silicon paints (or removes) both N and P type silicon doping onto the substrate.
• Metal paints (or removes) a metal layer and via placements.
• Execution compiles logic and prepares to execute it.
• ModuleEdit add, remove, and edit modules (I/O to/from the substrate).
• Label create a text label using Silicon paint.

Visual Mode (ESC)

Visual mode is accessed by clicking ESC from any other mode. While in visual mode you can perform the following actions:

• LMB Create a selection with LMB and dragging. Clear the selection with ESC or RMB.
• Y Copy ("yank") the current selection into the mouse-follow buffer. Use LMB to paste the mouse-follow buffer.
• D Copy the current selection into the mouse-follow buffer and delete the selection.
• Shift+D Delete the selection without copying it into the mouse-follow
• S+[0-9] With a selection or something currently in the mouse-follow buffer, you can hold S and click a number to 'store' that into a numbered register.
• [0-9] Once something is stored in a numbered register, you can load it into the mouse-follow buffer by clicking the number (without holding S).
• Shift+S+8 and Shift+8 Like VIM, there is a special register for copying/pasting into the system clipboard, the * register. This register will behave like the numbered registers, apart from the fact that it will always contain the system-clipboard value.
• R while the mouse-follow buffer is active to rotate it.
• M while the mouse-follow buffer is active to mirror it about the X axis.

Visual Mouse-follow Buffer

There is a special buffer that is used for copy-paste and rotation operations, the "mouse-follow buffer". It is filled when:

• A selection is yanked with Y, or deleted with D
• A named register is selected using [0-9] or *

While the mouse-follow buffer is active, it will show a preview of the results of placing the buffer onto the main blueprint, not the contents of the buffer itself. Meaning, the mouse-follow buffer can contain invalid connections (ie cells that claim to connect with a neighbor who doesn't connect back) and these broken connections will be 'stitched together' on-paste, when possible. The mouse-buffer is ephemeral and can be cleared at any time by clicking ESC or RMB. Additionally, clicking R will rotate the mouse-follow buffer 90 degrees clockwise, and M will mirror it across the X axis (use R, R, M to mirror about the X axis).

Silicon Mode (Q)

Silicon mode is accessed with the Q key. It is used for painting and erasing silicon doping. While in Silicon mode you can paint N and P type silicon, and form gates by dragging N-type on top of a P-type trace, or vice versa.

• LMB Paint a line of N-type silicon
• RMB (Or Shift+LMB) Paint a line of P-type silicon
• Ctrl+LMB Erase silicon of either type

Metal Mode (W)

Metal mode is accessed with the W key. It is used to connect Silicon together. It lives "above" the silicon and does not touch the silicon unless you place a via to connect them.

• LMB Paint a line of metal.
• RMB (Or Shift+LMB) Places a Via. Can only be used on a cell that has both metal and silicon and isn't a transistor.
• Ctrl+LMB Erase metal and vias.

Execution Mode (E)

Execution mode is accessed with the E key. It used to 'simulate' the substrate. It allows for both single-stepping as well as continuous running modes. Right now the only run mode is one fundamental clock per frame, but more will be added later for faster running.

• R Enters run-mode. This will execute one fundamental clock per frame.
• C Pauses run mode (if running) and executes a single fundamental clock.
• P Pauses run mode.
• T Executes a single simulation 'tick'. This is mostly for debugging Logic Paint itself, as ticks have very little parallel with propagation delay.

Module Edit (A)

The module edit mode is used to place, remove and edit modules. These include clocks, const values, probes and large chunks of RAM. Access the editor by pressing A while in Visual mode. Pressing A again cycles through module types that can be placed. While in Module Edit mode, you can visually see module "roots", ie the cell where the module actually resides. Only one module can exist per root at a time.

Label Mode (Enter)

Useful tool to quickly create text labels in Silicon. Enter the label mode by hitting Enter, then type your text. The text will be rendered to the mouse follow buffer. Clicking LMB will place a copy of the text (without the cursor) onto the primary buffer. Click ESC to exit label mode.

Scale and Performance

There are a handful of these projects out there, of note PharoChipDesigner has a wonderful writeup on both digital circuitry and how this type of logic differs from real-world MOSFET/BJT/CMOS technology. Also of note is Andre's Angular version as well as many more.

I wanted to build an entire CPU in this type of format (currently in-progress). No existing project comes remotely close to the level or performance or scale I needed for that. My ideal was fixed-cost rendering, and the ability to handle millions of transistors. Additionally, I wanted a much more refined and functional suite of design tools.

Logic Paint pulls that off by rendering cells exclusively in a fragment shader (on the GPU) meaning rendering is based only on the display resolution and is irrespective of the number of cells being drawn (modulo data transfer during simulation). It's not an exaggeration to say that the renderer can handle billions of populated cells on modern GPUs, it's limited only by your GPUs memory, where each cell takes up 4 bytes of data. However, the culling and sync code on my machine starts to chug at around 2 million cells. But I've done zero optimizations on it.

The core of the application is written in Rust, and compiled to WebAssembly. Right out of the box this gives you some immense performance wins, but more importantly it allows for directly memory manipulation and blitting which in tern allows for very fast designs.

Pics or it didn't happen

This is about a half million cells, rendering at 4K and taking only 2-3ms per frame. More cells wouldn't slow down rendering though, it would only create sampling artifacts and a colorful view. I get to about 2 million cells before the CPU-side of rendering calls start to chug. At 7 million cells I'm at 80ms frames.

License 🧾

Axum-Connect is dual licensed (at your option)

• MIT License (LICENSE-MIT or http://opensource.org/licenses/MIT)
• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)