[mbed boards] Packet drops cause failures

[polldo]

Background
Mbed boards (nano33ble, portentaH7) running ArduinoBLE have two relevant concurrent threads in execution: one executes the main arduino sketch, the other one handles the transport of HCI packets and stores the received ones in an internal buffer.
The thread executing the sketch should regularly call the BLE.poll() function to retrieve and analyze the packets stored by the other thread.

Problem:
If too much time passes between calls to the BLE.poll() function, then the buffer of received packets may become full. If it becomes full then the new packets received will be dropped. (see code)
This behaviour may result in a buffer overflow and consequently in a system crash.

Possible solutions

• Discourage the use of blocking functions (delay(millis) should be avoided. An alternative BLE.delay() that calls BLE.poll() could be implemented)
• Handle packets drop to prevent buffer overflows
• Increase the reception buffer to increase reliability in case some blocking function is essential.
• Stop the controller until some space is freed from the buffer (see #96)

Related issues
#126
#73
#102

[andbe-gh]

Hi @polldo,
the changes in HCICordioTransport.cpp (#96) seem to fix my problem (#126) with hanging arduino when many BLE devices are nearby. I've succesfully tested it with 32 devices.

[andbe-gh]

Is the problem fixed in the new release? I can't find anything in the changelog from 1.1.3 to 1.2.