micro-repl

Social Media Photo by Luca J on Unsplash

An easy, SerialPort based, MicroPython REPL for micro controllers.

• Live Board Demo
• Live PyScript Demo which uses MicroPython on the browser to communicate with the boards 🤯

Supported Boards

It is very likely that your MicroPython based board works too but these have been manually, and personally, tested during the development of this module:

• Spike Prime
• Raspberry Pi Pico and Pico W
• Adafruit PyPortal - CircuitPython
• Arduino Nano ESP32 I used dfu-util -a 0 -d 0x2341:0x0070 -D ./ARDUINO_NANO_ESP32-X.app-bin to install MicroPython on it: app-bin download

Features

The currently maintained and developed export is micro-repl/serial (previously known as board) which supports the following features:

• board name showed as soon as connected and associated to the board instance
• fully interactive REPL mode out of the box
• tab completion works out of the box too
• every Control+X combination just works
• stopping running code via Control+C also works
• pasting code also works
• paste mode never overflows the writes (big files copy pasted with ease)
• safe (after prompt) reboot on Control-D when not inside a paste mode session
• ondata(buffer:Uint8Array) passes along, while interacting, every single char the user is asking for
• AutoFit and WebLinks plugins available out of the box
• all imports are dynamic so it's size is still minimal before its usage
• eval method, if awaited and the end of the code has a reference, will return that value, if any, beside evaluating code without showing it on REPL shell. If the extra options reference hidden value is false, it also shows the evaluated code while streaming it to the board.
• paste method to pass along code in "paste mode" with ease

The micro-repl/board alias still exists but it's now micro-repl/serial instead, to eventually allow micro-repl/bt and others within the same ease of use.

How To / Documentation

The easiest way to use micro-repl/serial is via CDN:

<script type="module">
  import Board from 'https://esm.run/micro-repl/serial';

  // either Board(...) or new Board(...)
  const board = Board({
    // all optionals
    baudRate: 9600, // defaults to 115200
    onconnect() { console.info('connected') },
    ondisconnect() { console.warn('disconnected') },
    onerror(error) { console.error(error) },
    ondata(buffer) { },
    // pass a different JSON parser if needed: json.loads,
    // as example, would return directly Python references
    onresult: JSON.parse,
  });

  // to connect a board a user action/gesture is needed
  document.getElementById('repl').onclick = async event => {
    event.preventDefault();

    // connect the board to a DOM element to show the terminal
    await board.connect(event.target);
  };
</script>
<div id="repl"></div>

micr-repl/board TS signature

Documented via JSDoc TS, these are all explicit TS details around this module's API.

options

These are all optional fields that can be passed when creating a new Board.

type MicroREPLOptions = {
  // default: 115200
  baudRate?: number | undefined;
  // default: 'buffer'
  dataType?: 'buffer' | 'string';
  // default: console.error
  onerror?: ((error: Error) => void) | undefined;
  // default: () => void - notifies when the board is connected
  onconnect?: (() => void) | undefined;
  // default: () => void - notifies when the board is disconnected/lost
  ondisconnect?: (() => void) | undefined;
  // default: () => void - receives all data from the terminal
  ondata?: ((buffer: Uint8Array) => void) | undefined;
  // allow terminal easy-theme setup - if values are "infer"
  // these are retrieved via computed style / CSS values
  // for background (or background-color) and color (as foreground)
  // default: { background: "#191A19", foreground: "#F5F2E7" }
  theme?: {
        background: string;
        foreground: string;
    } | undefined;
}

board

A board can be created via new Board(options) or just direct Board(options) ( which is more Pythonic ) and its returned reference is always an instanceof Board.

type MicroREPLBoard = {
  // `true` when connected, `false` otherwise
  readonly connected: boolean;
  // the passed `baudRate` option
  readonly baudRate: number;
  // the connected board name
  readonly name: string;
  // the Terminal reference once connected
  readonly terminal: xterm.Terminal;
  // ⚠️ must be done on user action !!!
  // connects the board and show the REPL in the specified `target`
  // `target` can be either a DOM Element or an element ID or a CSS selector.
  connect: (target: Element | string) => Promise<MicroREPLBoard | void>;
  // disconnect the board and invoke ondisconnect
  disconnect: () => Promise<void>;
  // soft-reset the board and put it back into REPL mode
  reset: () => Promise<void>;
  // write any string directly to the board
  write: (code: string) => Promise<void>;
  // eval any code (no output while processing)
  // if the end of the `code` is a reference, it tries
  // to json serialize it and parse it back as result.
  // if the options.hidden is `false` it shows the input
  // while evaluating code.
  eval: (code: string, options?: { hidden:boolean }) => Promise<any>;
  // enter paste mode, write all code, then exit from paste mode
  paste: (code: string, options?: { hidden:boolean }) => Promise<void>;
}

Please note that board.write(code) requires \r\n at the end if you want your code to be executed.

Please also note this is not the same as board.terminal.write(...) because the terminal depends on writes on the board, not vice-versa.

WARNING

Please note this module is experimental. The current exports might change if actually the board reference is the best option this module offers (and I am definitively leading toward this conclusion).

Troubleshooting

If you are on Linux and you can't see your Prime you can try to force-enable it by writing the following content into /etc/udev/rules.d/50-myusb.rules:

KERNEL=="ttyACM[0-9]*",MODE="0666"

After a reboot, this instruction should enable it and you should see it selectable.

Credits

This project has been inspired by pyrepl-js but because I think React and TypeScript, plus the rest of the logic, was a bit too much for a basic core REPL, I've decided to create a minimal JS standard module able to do pretty much the same in way less code to maintain. Feel free to use that project if you want a more rich UI around the connection, events instead of just promises to deal with unbuffered data as sent by the controller, and everything else in there which I didn't need to create those live demoes.

micro-repl TS signature

deprecated

Once a repl has been successfully initialized, it offers this API:

// The default export TS signature
({ baudRate, onceClosed, }?: {
    baudRate: number; // default: 115200
    onceClosed(error: Error | null): void;
}) => Promise<{
    readonly active: boolean;
    readonly result: Promise<string>;
    readonly output: Promise<string>;
    write: (code: string) => Promise<...>;
    close: () => Promise<...>;
}>

Signature description

• repl.active as boolean - it's true when the REPL is active and running, false otherwise.
• repl.result as Promise<string> - it contains the last line produced by the last executed code.
• repl.output as Promise<string> - it awaits for the last executed code to execute and returns whatever that code produced, including the written code itself. Please note this throws an error if the active state is not true.
• repl.write(code) as (code:string) => Promise<void> - it writes code to the boards' REPL and it fulfills after all code has been sent. Please note this throws an error if the active state is not true.
• repl.close() as () => Promise<void> - it detaches all streams and gracefully clean up the repl state right before disconnecting it.

Example

// check the board status
repl.active; // true

// write code into the REPL
await repl.write('print("Hello MicroPython")');

// wait/check the produced REPL outcome
await repl.output;
/**
 * >>> print("Hello MicroPython")
 * Hello MicroPython
 */

// check the result (last printed line of the REPL)
await repl.result;  // "Hello MicroPython"

// disconnect the board
await repl.close();

// check the board status again
repl.active; // false