Serial I/O from mcsim to device connected over USB to host computer

[gingerbeardman]

Background

gingerbeardman:

Will mcsim, running as M5Paper, support serial i/o with a device connected over USB to my host PC? Please forgive my laziness on this question. Thanks!

phoddie:

No, not out-of-the-box. mcsim doesn't try to simulate hardware. But... there's a macOS implementation of ECMA-419 serial that should work. If you want to give it a try, I'm happy to help, but it could be a bit much for Twitter. ;) Just open a discussion on our GitHub repo.

Goal

My goal is to use my M5Paper as an I/O device for my Playdate handheld console, using serial over USB. This kind of comms is already possible using a PC.

I guess the first step is to create a small app to do serial I/O over USB from/to simulator to/from device?

Any pointers or help appreciated!

[phoddie]

The Moddable SDK is moving to using ECMA-419 for I/O, which includes serial. The ECMA-419 APIs are well supported on ESP32 and ESP8266, so you are set there.

On macOS, there are implementations of ECMA-419 Serial, TCP, UDP, and Listener I/O. Because ESP32 and macOS are very different operating systems,, there are differences in configuration. The APIs, however, are identical.

I built a small exampleI starting from the serial echo example. The modified version is configured for macOS and also outputs received bytes to the xsbug console. Here's the main.js script:

import Serial from "embedded:io/serial";
import TextDecoder from "text/decoder";

const decoder = new TextDecoder;
new Serial({
	device: "/dev/cu.usbserial-0001",
	baud: 74880,
	format: "buffer",
	onReadable: function(count) {
		const buffer = this.read();
		this.write(buffer);
		trace(decoder.decode(buffer, {stream: true}), "\n");
	},
});

Here's the manifest.json:

{
	"include": [
		"$(MODDABLE)/modules/io/manifest.json",
		"$(MODDABLE)/modules/data/text/decoder/manifest.json"
	],
	"modules": {
		"*": "./main"
	}
}

To test, I connected an ESP8266 to a USB port on my Mac (via a Moddable Programmer Serial-to-USB bridge) and hit the reset button to generate some bytes (the boot-loader's baud rate on ESP8266 is an unusual 74880). Adjust the device and baud as appropriate for your set-up.

[gingerbeardman]

Strange! It runs fine if I do mcconfig -d -m -p simulator (though I have to manually switch to M5Paper layout)
but errors if I do mcconfig -d -m -p simulator/m5paper

Any ideas @FWeinb ?

[FWeinb]

The syntax to start the simulator in a specific layout is mcconfig -d -m -p sim/m5paper

[phoddie]

This is a funny one. Something recently changed in the load order of simulators (probably when the Compartment API was updated) that causes the M5Paper simulator to generate an exception when selected at start-up. You can easily work around that by editing $MODDABLE/build/simulators/m5paper.js to add this before line 84 where the exception occurs:

      if (!globalThis.model) return;

With the change in place, everything – including serial – works normally.

I don't have time today to track down the root cause, but we'll sort that out.

FWIW – you can use both sim/m5paper and simulator/m5paper for the -p option when launching mcconfig.

[phoddie]

Just to close this out, the M5Paper simulator is using the model global. mcsim did not intend for that global to be available to simulator implementations, but it has been until recently. When updating mcsim to the latest Compartment API, the model global was made inaccessible to simulators leading to this exception. model is only used to access the current behavior, which happens to be this, so the code can be simplified to:

      const POWER_INFO_NAME = `POWER_INFO_${pin}`;
      if (POWER_INFO_NAME in this) {
        this[POWER_INFO_NAME].string = value ? "On" : "Off";
      }

This change will be incorporated into the next Moddable SDK, which will be live before the end of the week.

[gingerbeardman]

Thanks, that last one worked best for me. Onwards!