How to use the UART service.

[romw314]

I'm trying to create my own alternative to Pybricks Code (also a web app, in TypeScript and with Vue.js instead of React, but I think that this is not important), and my UART terminal does not work.

I use Xterm.js and write both to UART TX characteristic and to Pybricks Service (with header like Pybricks Code's) when user types into terminal.

Here is a simplified example of my code:

const device = await navigator.bluetooth.requestDevice({
	filters: [{ services: [pybricksServiceUUID] }],
	optionalServices: [nordicUartServiceUUID]
});
console.log('Connecting to device...');
const gatt = await device.gatt!.connect();
const nordicUartService = await gatt.getPrimaryService(nordicUartServiceUUID);
const nordicUartRxCharacteristic = await nordicUartService.getCharacteristic('6e400002-b5a3-f393-e0a9-e50e24dcca9e');
const nordicUartTxCharacteristic = await nordicUartService.getCharacteristic('6e400003-b5a3-f393-e0a9-e50e24dcca9e');

nordicUartTxCharacteristic.addEventListener('characteristicvaluechanged', () => {
	// here it's simplified. but in my app I also write to my Xterm.js instance here.
	console.log('Got UART data', nordicUartTxCharacteristic.value!.buffer);
});

// HACK: see https://github.com/pybricks/pybricks-code/blob/4c364e7fd57c6b06a5cc390d07876d6df4aa7a32/src/ble/sagas.ts#L438-L444
await nordicUartTxCharacteristic.stopNotifications();
await nordicUartTxCharacteristic.startNotifications();

• PC-to-Hub: When i write into the terminal, it works only when I'm connected both to my app and to Pybricks Code, otherwise it does not work.
• Hub-to-PC: Does not work at all.

[dlech]

We no longer use the nordic uart service in the firmware. So unless you want to support really old firmware versions, you don't need that part.

However, 6e40000X-b5a3-f393-e0a9-e50e24dcca9e is the Pybricks characteristics, not the nordic uart ones, so it looks like your code is trying to mix the two.