Problem after BLE connect/disconnect

[marco]

I’m trying to put together something that would have one BLE module working as an iBeacon, and a second one as a BLE master that scans and discovers services from nearby devices.

But I’m having some trouble to make this work properly. I think I’ve read pretty much everything on the web trying to find an answer.
Since I want to discover device services, each time the Tessel finds a new BLE, it will try to connect to it and fetch the available services. The problem is that right after the Tessel finishes the connects/disconnects process on all found devices, it seems to freeze everything else (ibeacon and scanning).

I’m not sure if this is a Tessel issue or something that I might be doing wrong, so I’m attaching the source code so you can take a look.

Here's the source code I'm using.

[jon]

@marco,

I'm walking through your code now. Why do you set a timeout to disconnect from the device one second after you connect? If the Tessel is in the middle of discovering all the services on the remote BLE device and is told to disconnect in the middle, you may have undesired behavior.

-Jon

[marco]

The idea is to give a connection timeout.
One of the reasons is that nearby devices won't give that much more time to the connection. The other is that I'm assuming discovering the services shouldn't take that long.
Of course the timeout can be increased if necessary, or even removed since the nearby device will close it.

[jon]

Could you remove that timeout and see if it helps at all?

You'll get a disconnect event if the remote device closes the connection on its own.

-Jon

[marco]

Removing the timeout doesn't seem to change anything, except for the iBeacon which keeps running. So only port B process freezes, which is the one used for the ble scan.
What would be the reason for not being a good idea to disconnect from nearby devices?

The other reason that i forgot to mention why i'm disconnecting, is that since the BLE module can only handle 4 connections at the same time (from the reading i've done), I want to disconnect as soon as the tessel has all it needs, and proceed to the next one.
The real scenario might involve over 100 devices to go through.

[marco]

It's been 4 days since my last post?
Any ideas would be really helpful.

[jon]

Hi @marco,

I can try to reproduce this test case tomorrow. Just to be sure I understand, you're running to BLE devices off the same Tessel. One is ran as a beacon and the other is a master. Once the master discovers the iBeacon, both devices freeze up?

How long have you waited for the service discovery event to be called? Can you blink LEDs on an interval on both BLE modules and see if code actually freezes?

-Jon

[marco]

About what each BLE module does, thats correct.

The scanner is not looking for iBeacons, it will find any nearby BLE device and try to discover all available services.
Once discovered, it will connect() to that peripheral and that's where it all hangs.

As you can see from the source code, the two leds are being used, one as an iBeacon status light (on/off) and the other will blink each time the scanner finds a peripheral.
The iBeacon led (blue) will stay on forever, but an iBeacon scanner app (ie Beacon Scout for Android) can easily show when the iBeacon is actually being advertised. The scanner led will stop blinking as soon as the connect() kicks in.

[jon]

@marco,

I dug into it today and found what was freezing the program. For some reason, JSON.stringify(services) is going into an infinite loop. This is a runtime issue and I've opened a relevant issue.

For now, just change line 109 from:

console.log('got services!', JSON.stringify(services));

to

console.log('got services!', services.toString());

[marco]

Hi @jon,

I made the change, but apparently nothing changed on my side.

I'm basically testing the code with and without the scanner.connect(peripheral) on the 'discover' event.

By commenting out the connect function, the logs keep spitting out the discovered peripherals. With the connect() the log just stop running.

[jon]

@marco,

If you connect to a slave from the master, it will stop discovering more peripherals unless you explicitly tell it to start discovering again.

I've written up a gist of how to do it here. Note that my gist also commands the iBeacon to start advertising again after a disconnect event.

[marco]

@jon,

Ah, that makes things more clear and actually makes sense for the antenna to stop scanning while connecting.

But that reminds me of the limit to connect to 4 different peripherals at a time.
Does that mean the module can for example connect to only 3 and keep scanning with the 4th "slot", or that it's either scanning or connecting, whatever the connection limit is?

I will do some tests and get back with a status update.

Edit:
Tessel is not freezing anymore. Thanks!

[jon]

@marco,

I believe you can continue scanning no matter how many devices are connected but I haven't tested that out on my end. If you try it, let me know how it goes?

-Jon

[marco]

@jon,

Is there any way to make the tessel keep scanning while connecting to devices in parallel?

[jon]

@marco,

Can you simply start scanning after being connected?

ble.on('connect', function() {
  ble.startScanning();
});

-Jon

[marco]

@jon,

I was just curious on wether there was a flag that could be turned on to make the tessel not stop scanning. That would be helpful.

I'll use that snippet meanwhile.

Cheers

[cybereye]

@macro

I think you are looking for below codes :

ble.startScanning({allowDuplicates:true});

Default API (without parameters) skips duplicated devices to report again,
actually it wouldn't stop to searching until you provide a stop API.