NRF multiple connections?

Having 5 pucks at hand I'd like to do some round-robin communication:

• request a list of available pucks around me (works)
  
• iterate through the list (issue A below)
  
• receive feedback during the UART connection (issue B below)
  
  

I am aware, that connection multiple peripherals at the same time is not possible atm, so I do it sequentially (with recursive callbacks).

This is my connection code:

function transfer(device, text, callback) {
  var char;
  var result = "";
  console.log( "connecting " + device.name );
  return device.gatt.connect().then(function(d) {
    device = d;
    console.log( "connected" );
    return d.getPrimaryService("6e400001-b5a3-f393-e0a9-e50e24dcca9e");
  }).then(function(s) {
    console.log( "service found" );
    return s.getCharacteristic("6e400002-b5a3-f393-e0a9-e50e24dcca9e");
  }).then(function(c) {
    char = c;
    console.log( "characteristic found" );
    function sender(resolve, reject) {
      console.log( "sending" );
      if (text.length) {
        char.writeValue(text.substr(0,20)).then(function() {
          sender(resolve, reject);
        }).catch(reject);
        text = text.substr(20);
      } else  {
        resolve();
      }
    }
    return new Promise( sender );
/* 
   }).then(function() {
    function receiver(resolve, reject) {
      console.log( "receiving" );
      char.readValue().then(function(chunk) {
        console.log(chunk);
        if( chunk.length > 0 ) {
          result += chunk;
          receiver(resolve, reject);
        }
        else {
          resolve();
        }
      }).catch(reject);
    }
    return new Promise( receiver ); */
  }).then(function() {
    device.disconnect();
    if (callback) callback(result);
  });
}

Issue A:
As long as I disable (/**/) the receiving part I can pass commands to the first puck successfully.
But when I try to connect the second one I get BLE error 18 - why?

found Puck.js f002
found Puck.js 38a4
found Puck.js c9fc
connecting Puck.js c9fc
connected
service found
characteristic found
sending
sending
done
connecting Puck.js 38a4
Uncaught Error: Unhandled promise rejection: Error: Got BLE error code 18

Question: What does that mean and what can I do about it?

Issue B:
I also like to get the feedback of the command sent to the pucks.
So I tried to add the receiver part (in comments) but it always receives the echo of the data I just sent.

Question: How can I get the full response and how do I detect the end of a transmission?

I'll upload the full sourcecode as attachment so you have the complete picture.

Thanks in advance,
Christian

1 Attachment

• spread.js

Try adding a delay between disconnecting from one puck and connecting to the other. Disconnect starts a disconnect but it takes some time to complete, and the web Bluetooth spec doesn't seem to remove a return a promise.

Unfortunately notifications aren't implemented yet, so you can't get the result. It'll be in a firmware update in the new year though

Thanks again, Gordon.

Adding the timeout solved it:

scan( function( queue ) {
    // recurse through queue
    function process() {
      if( queue.length ) {
          transfer( queue.pop(), command, function( result ) {
            console.log( "done" );
            setTimeout( process, 150 );
          });
      }
    }
    process();
  });

150 ms seems sufficient.
I was able to go down to about 145 ms, but everything below still caused some errors.

I'm very thrilled to get the notifications.
Good work - keep it up!