Arduino Nano 33 IoT large transfer fix (MCU hang bug)

[coderand]

uint16_t handle = *(uint16_t*)data

hangs Arduino Nano 33 IoT in cases when data pointer is unaligned. This happens when receiving large packets of BLEStringCharacteristic.

Cortex®-M0 does not support unaligned memory access.

This doesn't not happen when setting such characteristics from iPhone (iOS) or Android devices, but happens 100% of the time on PC using either Bleak (Python) or QT6 libraries.

In those cases data pointer at the time of this call is not two bytes (sizeof(uint16_t)) aligned and dereferencing such pointer hangs the MCU.

To resolve the issue we copy that uint16_t handle byte by byte without monkeying with ORs, Shifts or other binary operations to avoid endianness issues on other platforms.

[CLAassistant]

All committers have signed the CLA.

[coderand]

Alternatively, instead of uint16_t handle = *(uint16_t*)data;
it could be:
uint16_t handle;
memcpy(&handle, data, sizeof(handle));
that's a bit more consistent with the rest of the coding style there.

Apart from that, it looks like there could be a few more potential bugs of this sort but I have no way to test or confirm those. The most obvious one would probably be in ATTClass::readOrReadBlobReq method, where uint8_t data[] is dereferenced as *(uint16_t *)data as well.

[coderand]

This mainly happens when setting long values such as "012345678901234567890123456789" on Windows 10 using pretty much any BLE tool or API. Writing characteristic with "Microsoft LE Expolorer", using Python/Bleak or Qt6

The Arduino NANO 33 IoT Sketch is:

#include <ArduinoBLE.h>
#include <utility/ATT.h>
#include <utility/GATT.h>

BLEService testService("180B");
BLEStringCharacteristic testCharacteristic("00000003-0000-1000-8000-00805f9b34fb", BLEWrite | BLERead | BLENotify, 185);

void setup() {
  Serial.begin(9600);
  while (!Serial);

  ATT.setMaxMtu(185);

  if (!BLE.begin()) {
    while (1);
  }

  GATT.setDeviceName("IoT-Hang");
  BLE.setLocalName("IoT-Hang");
  BLE.setDeviceName("IoT-Hang");
  BLE.setAdvertisedService(testService);
  testService.addCharacteristic(testCharacteristic);
  BLE.addService(testService);
  BLE.advertise();
}

void loop() {
  BLEDevice central = BLE.central();

  if (central && central.connected()) {
    if (testCharacteristic.written()) {
      Serial.println(testCharacteristic.value());
    }
  }
}