How to setup a custom NRF Service on Bangle.js 2

[leonkansti]

Hello, as the title suggests i am trying to set a custom service to send some health data that i record and safe locally on the watch to my smartphone. Therefore i am trying to create a NRF service but unfortunately its not working. I cant find the service even though i wrote the code into a boot.js file which should be running whenever the watch starts, right. Let me share you my code, especially the part with NRF.Services should be relevant. What am I doing wrong?

All the best

Leon

(function(){
  // BLE: Custom GATT Bulk Characteristic für alle Messwerte (liest healthdata und leert sie)
  function getAndClearAllHealthData() {
    try {
      var storage = require('Storage');
      var file = storage.open('healthdata', 'r');
      if (!file) return null;
      var results = [];
      var line;
      while ((line = file.readLine()) !== undefined) {
        if (line.length > 0) {
          var parts = line.split(',');
          if (parts.length >= 7) {
            results.push({
              timestamp: parts[0],
              bpm: Number(parts[1]),
              steps: Number(parts[2]),
              temp: Number(parts[3]),
              stress: Number(parts[4]),
              motion: Number(parts[5]),
              rhr: Number(parts[6])
            });
          }
        }
      }
      // Nach erfolgreichem Lesen Datei löschen
      storage.open('healthdata', 'w');
      return JSON.stringify(results);
    } catch(e) {
      return null;
    }
  }

  NRF.setServices({
    "12345678-1234-5678-1234-56789abcdef0": {
      "12345678-1234-5678-1234-56789abcdef1": {
        readable: true,
        notify: true,
        value: [0],
        description: 'All Measurements (JSON-Array)',
        onRead: function() {
          var data = getAndClearAllHealthData();
          return data ? data : '[]';
        }
      }
    }
  }, { advertise: ["12345678-1234-5678-1234-56789abcdef0"]});
})();

[gfwilliams]

Hi Leon,

Did you find code as an example somewhere that you based this off, or was this an AI suggestion? The problem is the onRead field you're relying on in setServices doesn't exist - see https://www.espruino.com/Reference#l_NRF_setServices

There isn't enough time to come up with data in time to send it to the connected computer, so you have to set the value ahead of time - it's not possible to have an onRead function - and anyway the max size of data you can transfer over a characteristic is usually pretty limited (~120 bytes on Bangle.js I think) so likely this method wouldn't work anyway.

It's odd the new characteristic doesn't appear - usually if you're connected to the device when you run the code you'll see some kind of message if something has gone wrong... Maybe put in some print statements to ensure it's actually running?

To transfer the data you can create 2 characteristics - one that can be watched with 'notify' for data to be pushed out of it, and one that the client can write to to set it off. To push data out of a 'notify' service you use NRF.updateServices, there's an example at: https://www.espruino.com/Reference#l_NRF_updateServices

But really, this kind of thing is what the Bluetooth UART characteristic that's built into Bangle.js is great for - your client can just connect to the Bangle and listen on the Nordic UART characteristics it provides, and you just use print/console.log in Bangle.js and it'll output the data through the characteristic automatically - that's what I'd suggest

[leonkansti]

Hi, thank you for the reply!

I've already got the functionality working with Nordic UART. It works quite reliably. I just thought it might be more standardized (for example, with other open-source clocks like the Pine Time) if I use a custom characteristic for the transmission. I'll experiment with it a bit more, but if it doesn't work, I'll switch back to Nordic UART. I wasn't aware there was a data limit with custom characteristic; that probably makes it unsuitable anyway.

[enaon]

I think you are missing the NRF.setAdvertising part.

this is a working example, not bangle based but maybe helpfull

ew.comm.updt = function() {

  let updateAdv = function() {
    const role = { "watch": [0, "eW"], "litterBox": [1, "eL"], "tag": [2, "eC"], "pb": [3, "eR"], "light": [4, "eT"], "blind": [5, "eB"], "pir": [6, "eP"] };
    const phy = ["1mbps", "2mbps", "coded", "coded,1mbps", "1mbps,coded"];
    const board = ["MAGIC3", "ROCK", "BANGLEJS2", "DSD6", "NANO", "P8", "P22"];
    const txPower = [-8, -4, 0, 4, 8];

    var roleByte = 0;
    if (Array.isArray(ew.def.role)) {
      for (var i = 0; i < ew.def.role.length; i++) {
        var r = ew.def.role[i];
        if (role[r][0] !== undefined) {
          roleByte |= (1 << role[r][0]);
        }
      }
    }
    else {
      roleByte = (1 << role[ew.def.role][0]);
    }
    if (ew.def.frce === undefined) ew.def.frce = 0;

    return {
      name: (Array.isArray(ew.def.role) ? role[ew.def.role[0]][1] : role[ew.def.role][1]) + "-" + ew.def.name,
      showName: true,
      manufacturer: 0x0590,
      manufacturerData: [
        roleByte,
        (ew.def.bt.conn ? 1 : 0) | (ew.def.bt.uart ? 2 : 0) | ((phy.indexOf(ew.def.bt.phyA)) << 2) | ((txPower.indexOf(ew.def.bt.rfTX)) << 5), //bt info
        ew.sys.batt(1),
        ew.sys.batt() * 100 / 2 | 0,
        board.indexOf(process.env.BOARD) | ((ew.def.frce ? 1 : 0) << 4) //board type
      ],
      connectable: (ew.def.bt.conn ? true : false),
      scannable: (ew.def.bt.phyA === "1mbps" ? true : false),
      phy: ew.def.bt.phyA,
      interval: ew.def.bt.intA
    };

  }
  let secureMode=ew.def.bt.pair?{passkey:ew.def.bt.code, mitm:1, display:1}:{};

  try {
    
    NRF.setAddress(`${NRF.getAddress()} random`);
    NRF.setSecurity(secureMode);

    if (ew.def.bt.conn)
      NRF.setServices({
        0xffe0: {
          0xffe1: {
            value: [0x01],
            maxLen: 128,
            writable: true,
            onWrite: function(evt) {
              ew.comm.prfr.RX(evt.data);
            },
            security: {
              read: {
                mitm: ew.def.bt.pair1?true:false,
                encrypted: ew.def.bt.pair1?true:false
              },
              write: {
                mitm: ew.def.bt.pair1?true:false,
                encrypted: ew.def.bt.pair1?true:false
              },
            },
            readable: true,
            notify: true,
            description: "eW"
          }
        }
      }, { uart: (ew.def.bt.uart) ? true : false });


    if (ew.def.bt.adv) {

      NRF.setAdvertising({}, updateAdv());

      if (ew.is.btsl == 1) {
        NRF.wake();
        ew.is.btsl = 0;
      }
      NRF.setConnectionInterval(ew.def.bt.intC);
      NRF.setTxPower(ew.def.bt.rfTX);
    }
    else {
      //if (ew.is.bt) NRF.disconnect();
      NRF.sleep();
      ew.is.btsl = 1;
    }

  }
  catch (e) {
    if (ew.dbg) console.log("comms: Bt update error: ", e);
    ew.sys.fileWrite("error", "er", e);
  }
};

[leonkansti]

@enaon when using NRF.setAvertising it actually works to the point i can atleast see my service. But only if use a 16bit UUID not with 128bit UUIDs. Anyway, thanks!

@gfwilliams I do not quite get why the transfer size should be an issue, as i can send my data in chunks. Because thats what i am doing with nordic UART anyway and i dont quite understand in what way a custom service actually differs from the nordic UART.

Sorry if thats a bit nooby, i am just learning about all this stuff

[enaon]

sorry for answering this, I am not sure I should. The MTU size is not that important, you can do chunks, the main difference is that the nordic service handler is builtin to the firmware, where a custom one needs a function written in JavaScript, I think it is faster and lower on resources. But a custom one is fine, I use custom characteristics without any problems.

[leonkansti]

thank you, i will try it out and see what suits me better!