5 years, 3 months ago.

Is offset for BLE read long values in use?

Hi there,

I'm trying to read from a GATT client a characteristic with 29 bytes, this is, a long characteristic value. It only reads the first 22 bytes, this is, the first chunk of data sent by the GATT server. I know the server can send the full 29 bytes since I have tested using a phone app to access the server just to see in which side of the communication was the problem.

I have tracked backwards the DiscoveredCharacteristic::read(...) function all the way up to BlueNRGGattClient::read function where I've found that the offset argument sent to this function is fully ignored in its implementation, as can be seen below...

ble_error_t BlueNRGGattClient::read(Gap::Handle_t connHandle, GattAttribute::Handle_t attributeHandle, uint16_t offset) const
{
  /* avoid compiler warnings about unused variables */
  (void)offset;

  tBleStatus ret;

  BlueNRGGattClient *gattc = const_cast<BlueNRGGattClient*>(this);

  // Save the attribute_handle not provided by evt_att_read_resp
  gattc->readCBParams.handle = attributeHandle;

  // FIXME: We need to wait for a while before starting a read
  // due to BlueNRG process queue handling
  Clock_Wait(100);

  ret = aci_gatt_read_charac_val(connHandle, attributeHandle);

  if(ret == BLE_STATUS_SUCCESS) {
    gattc->_currentState = GATT_READ_CHAR;
    return BLE_ERROR_NONE;
  }
  switch (ret) {
  case BLE_STATUS_BUSY:
    return BLE_STACK_BUSY;
  default:
    return BLE_ERROR_INVALID_STATE;
  }
}

As you can see, the code calls aci_gatt_read_charac_val(connHandle, attributeHandle) and do not pass along the offset value. But what is more strange to me is that there is another function aci_gatt_read_long_charac_val(...) which does use a third argument with the offset, but this function is not being used.

Why ? Is the read of long value characteristics possible with this library or not (maybe I'm looking the wrong functions) ?

Thanks.