setAdvertisting serviceData data length max?

[espruino-discuss3]

Posted at 2018-05-20 by Enclavet

Trying to advertise last button press epoch time. Whenever I do something like the following:

var buttonEpoch = 0;

function updateAdvertising() {
    data = totpObj.getOTP("");
    NRF.setAdvertising({0xFFFF : [buttonEpoch]});
}

setWatch(function() {
    var epoch = Math.round(new Date().getTime() / 1000.0);
    buttonEpoch=epoch;
    updateAdvertising();
}, BTN, { edge:"rising", repeat:true, debounce:50 });

Seems like the serviceData is only 2 bytes. Is this a known limitation of using advertising for data?

I am able to put large integers into the manufacturing data but i'm using that now and dont have enough room.

[espruino-discuss3]

Posted at 2018-05-21 by Enclavet

So actually I figured it out that I was running int he max_size of a single advertistment packet.

I instead tried to split it up into 2 advertistment packets but it was not working right. Is the below code something that should work?

NRF.setAdvertising([{0xFFFF : [buttonEpoch]},{0x180F:[batteryLevel]}]);

---

Posted at 2018-05-21 by @gfwilliams

the code you have should work, but you're supplying an array with one element, so it'll only be sending one byte (0..255) worth of data.

You can do:

NRF.setAdvertising({0xFFFF : [buttonEpoch>>24,buttonEpoch>>16,buttonEpoch>>8,buttonEpoch]});

which will transmit 4 bytes that can be reconstructed into a 32 bit int. Normally you'd have ... &255 there but it's sort of implicit since only the bottom 8 bits of each element is used anyway.

If you want something that looks a bit nicer you can use DataView instead of all the bit shifting too.