accelerometer data over Bluetooth does not work

[smartyw]

With the accelerometer service included in a hex file by including the following line of code:

    new MicroBitAccelerometerService(*uBit.ble, uBit.accelerometer);

it should be possible for a connected Bluetooth client like a smartphone to switch on accelerometer data notifications. After enabling notifications, none are ever received however.

Here's a simple test application:

/**
 * This is a simple template for use with Calliope mini.
 *
 * @copyright (c) Calliope gGmbH.
 * @author Matthias L. Jugel.
 *
 * Licensed under the Apache License 2.0
 */

#include <MicroBit.h>

MicroBit uBit;

void onConnected(MicroBitEvent)
{
    uBit.display.scroll("C");
}

void onDisconnected(MicroBitEvent)
{
    uBit.display.scroll("D");
}

int main(void)
{
    uBit.init();
    uBit.serial.baud(115200);
    uBit.serial.send("Calliope BLE accelerometer test v1.0\r\n");
    uBit.display.scroll("BLE ACC");
    uBit.messageBus.listen(MICROBIT_ID_BLE, MICROBIT_BLE_EVT_CONNECTED, onConnected);
    uBit.messageBus.listen(MICROBIT_ID_BLE, MICROBIT_BLE_EVT_DISCONNECTED, onDisconnected);

    uBit.accelerometer.setRange(8);
    new MicroBitAccelerometerService(*uBit.ble, uBit.accelerometer);

    release_fiber();
}

Furthermore, reading the Accelerometer Data characteristic always returns a value of zero. Here's a screenshot of nRF Connect showing this:

I investigated and found a clue.

There are two accelerometer drivers in the source tree. One of them creates events for component ID MICROBIT_ID_ACCELEROMETER (=4) and the other uses component ID (BMX055_ACC_ADDRESS<<1)=48.

The MicroBitAccelerometerService.cpp class registers for events from MICROBIT_ID_ACCELEROMETER but never receives any callbacks for that event.

I changed MicroBitAccelerometerService.cpp to register for events from component ID 4:

     printf("About to register for accelerometer events\r\n");
    if (EventModel::defaultEventBus) {
        int id = BMX055_ACC_ADDRESS<<1;
        printf("id=%d\r\n",id);
        EventModel::defaultEventBus->listen(id, MICROBIT_ACCELEROMETER_EVT_DATA_UPDATE, this, &MicroBitAccelerometerService::accelerometerUpdate,  MESSAGE_BUS_LISTENER_IMMEDIATE);
    }

But this made no difference. Callbacks were not received.

As an experiment, I then registered for the same events from MICROBIT_ID_ACCELEROMETER from within my main method, like this:

 int main(void)
{
    uBit.init();
    uBit.serial.baud(115200);
    uBit.serial.send("Calliope BLE accelerometer test v1.0\r\n");
    uBit.display.scroll("BLE ACC");
    uBit.messageBus.listen(MICROBIT_ID_BLE, MICROBIT_BLE_EVT_CONNECTED, onConnected);
    uBit.messageBus.listen(MICROBIT_ID_BLE, MICROBIT_BLE_EVT_DISCONNECTED, onDisconnected);

    uBit.accelerometer.setRange(8);
    new MicroBitAccelerometerService(*uBit.ble, uBit.accelerometer);

    // id =    BMX055_ACC_ADDRESS<<1;
    // MICROBIT_ID_ACCELEROMETER, MICROBIT_ACCELEROMETER_EVT_DATA_UPDATE

    int id =    BMX055_ACC_ADDRESS<<1;

    uBit.serial.printf("MICROBIT_ID_ACCELEROMETER: %d\r\n",MICROBIT_ID_ACCELEROMETER);
    uBit.serial.printf("id                       : %d\r\n",id);

   uBit.messageBus.listen(MICROBIT_ID_ACCELEROMETER, MICROBIT_ACCELEROMETER_EVT_DATA_UPDATE, onAccelerometerUpdate);

    release_fiber();
}

Now I receive callbacks in the accelerometer service class and the Bluetooth accelerometer service is working.

So, somewhere I think there's a mix up with component IDs used for events. I'm also not sure why you include both accelerometer drivers in the build. Is that deliberate or a mistake?