More than 3 concurrent BLE Connections (Arduino Nano 33 BLE)

[Dorsel89]

Hi everyone,
I would like to have more than 3 concurrent BLE connections with the Arduino Nano 33 BLE. As far as i understand i have to adjust the DM_CONN_MAX in cfg_stack.h.

Unfortunately, that doesn't work, do you have any tips on what I'm doing wrong?
Thanks and kind regards!

[sandeepmistry]

Hi @Dorsel89,

I believe the link layer inside libmbed.a will need to be re-compiled for the changes to take effect. I also believe variants/ARDUINO_NANO33BLE/mbed_config.h is the correct place to update the define.

There is a script to re-compile mbed: https://github.com/arduino/ArduinoCore-nRF528x-mbedos/blob/master/mbed-os-to-arduino

[Dorsel89]

Hi @sandeepmistry
thanks for your help! I followed your suggestions but I am still not able to connect more devices (or less after I decreased DM_CONN_MAX).

I wonder about the mbed_config.h , in the header it is mentioned that the file should not be edited, because the values are generated automatically. This is exactly what I noticed, after I start the script mbed-os-to-arduino all defines are back to default.

It would be nice if you have more tips for me!

edit: I used the script with these parameters:
./mbed-os-to-arduino -c ARDUINO_NANO33BLE:ARDUINO_NANO33BLE

[sandeepmistry]

Hi @Dorsel89,

I've just spoken to @facchinm about this, the correct place to add the define is in variants/ARDUINO_NANO33BLE/conf/mbed_app.json, then re-compile mbed.

Apologies for the incorrect information I provided earlier.

[Dorsel89]

Hey @sandeepmistry,

thanks for your help! I just managed to override DM_CONN_MAX. Will check if it really works now =)

Thanks in advance

[Dorsel89]

Hi @sandeepmistry,
I would like to sum up my current results. I edited my mbed_app.json, recompiled everything, and be able to connect up to 8 devices to my arduino.

I found the right macro names in this file (mbed-os repository) : mbed_lib.json.

Unfortunately I cannot increase the maximum number of connections. If I set max-connections to something >8 the BLE Server does not start. Maybe I have to increse some memory size? If yes, where? But I have to admit, I actually dont know how to debug this right now.

[facchinm]

Hi @Dorsel89 ,
sorry for the late response but I missed this thread. It could indeed be a memory limitation related to ble thread; if so, you could try increasing the allocated memory here (https://github.com/arduino-libraries/ArduinoBLE/blob/master/src/utility/HCICordioTransport.cpp#L164) so that line reads

static rtos::Thread bleLoopThread(osPriorityNormal, PREFERRED_STACK_SIZE);

By increasing PREFERRED_STACK_SIZE (from the initial 4KB) you can check if the BLE server starts again.

[Dorsel89]

Hey @facchinm,

I just checked if the Bluetooth Server starts by changeing:

A) increase the STACK_SIZE of the bleLoopThread
and
B) increase the MBED_CONF_RTOS_THREAD_STACK_SIZE with the mbed_app.json

Of course both should do the same in the end, both ways do not work for max-connections = 9. I changed the size to 2*4096 for both ways.

Do you have any further ideas?

Many Thanks

[gnsmrky]

@Dorsel89 Can you share how you managed to do multiple concurrent connections? I have Arduino Nano 33 BLE acting as central. Only got 1 peripheral connection. 2nd connection always fails.

[polldo]

@gnsmrky you can follow this issue arduino-libraries/ArduinoBLE#108

[Dorsel89]

Hey @gnsmrky & @polldo ,
sorry for my late response. You can take a look at this library:

https://github.com/Dorsel89/phyphox-arduino

I just tested the example "randomNumbers" and it works on 2 phones at the same time for me. It should work up to 3 concurrent connections without changing the mbed_app.json. If you change the mbed_app.json as discussed in this issue you can get up to 8 connections. Unfortunately i did not manage to get more connections but it is still on my todo list.

Hope this helps

edit: I'm using the board driver: Arduino nrf528x Boards(Mbed OS) V 1.1.4

[Dorsel89]

Hey @giulcioffi,

is there reason to stick at 5 connections? In general I would like to get up to 20 connections but I couldnt figure out why my bluetoothserver crashed with DM_CONN_MAX>8. Unfortunately this topic is not on top of my TODO list so I didnt spent any time on this since months..