Received empty data array after notification

[ilockit_CFR]

Hi,

I adapted the nus_client from the Nordic Connect SDK v2.7.0. I changed the UUID and some function names, but in general the code stays the same. I can subscribe one of the characteristics and receive data from it. But the problem is, that everytime I receive a notification, I get another receive event with an empty data array. This leads to an unsubscribtion of the characteristic. 

00> D: [NOTIFICATION] data 0x2000d40c length 4
00> D: ble_mode_data_received
00> data: 01000000
00> D: [NOTIFICATION] data 0 length 0
00> D: [UNSUBSCRIBED]

The client only sends notifications with length = 1, so it's unlikely that the event comes from the client. The client is implemented in nrf5 SDK and sends data with the following code:

void ble_fob_on_mode_change(uint16_t conn_handle, ble_fob_t * p_fob, uint8_t mode_state)
{
    ble_gatts_value_t gatts_value;
    
    // Initialize value struct.
    memset(&gatts_value, 0, sizeof(gatts_value));

    gatts_value.len     = sizeof(uint8_t);
    gatts_value.offset  = 0;
    gatts_value.p_value = &mode_state;
	
    sd_ble_gatts_value_set(conn_handle,
                            p_fob->mode_char_handles.value_handle,
                            &gatts_value);
    
    // send notification
    if(conn_handle != BLE_CONN_HANDLE_INVALID)
    {
        ble_gatts_hvx_params_t params;
        uint16_t len = sizeof(mode_state);

        memset(&params, 0, sizeof(params));
        params.type   = BLE_GATT_HVX_NOTIFICATION;
        params.handle = p_fob->mode_char_handles.value_handle;
        params.p_data = &mode_state;
        params.p_len  = &len;

        sd_ble_gatts_hvx(conn_handle, &params);
    }
}

How can I resolve this problem?

Best regards,

Christian

[Turbo J]

Triple-check the return code of your notification function. A return value of BT_GATT_ITER_STOP will automagically unsubscribe!

[ilockit_CFR]

Hi, 

the only place where BT_GATT_ITER_STOP is returned is when the [UNSUBSCRIBE] happens. I attached the wireshark file for the connection.

 keyfob_unsubscribe.pcapng

At the same time these were the logs of the peripheral:

00> D: Connecting (0)
00> I: Connected
00> 
00> D: Security changed: E7:B8:CB:8B:91:F8 (random) level 2
00> D: The discovery procedure succeeded
00> D: Getting handles from service.
00> D: Found handle for mode characteristic.
00> D: Found handle for CCC of mode characteristic.
00> D: Found handle for serial characteristic.
00> D: [SUBSCRIBED] mode characteristic
00> D: [NOTIFICATION] data 0x2000e34c length 4
00> D: ble_mode_data_received
00> data: 01000000
00> D: [NOTIFICATION] data 0 length 0
00> D: [UNSUBSCRIBED]
00> D: ble_mode_unsubscribed
00> D: [SUBSCRIBED] mode characteristic
00> D: [NOTIFICATION] data 0x2000e34c length 4
00> D: ble_mode_data_received
00> data: 00000000
00> D: [NOTIFICATION] data 0 length 0
00> D: [UNSUBSCRIBED]
00> D: ble_mode_unsubscribed
00> D: [SUBSCRIBED] mode characteristic

At the moment I use a workaround and subscribe everytime when the characteristic gets unsubscribed. This is why there are more than one [SUBSCRIBED] messages.

I hope this helps.

Christian

[Sigurd]

ilockit_CFR said:

I attached the wireshark file for the connection.

unfortunately, the connection is encrypted, and the sniffer did not have the keys, so could not read much from that log.

 

https://docs.nordicsemi.com/bundle/nrfutil/page/nrfutil-ble-sniffer/guides/common_actions_sniffing_conn_bonded_devs.html 

https://docs.nordicsemi.com/bundle/nrfutil/page/nrfutil-ble-sniffer/guides/common_actions_sniffing_pairing_procedure.html

[ilockit_CFR]

Thanks for the reply. I tried it again with your instructions and received this: 

6874.keyfob_unsubscribe.pcapng

[Sigurd]

Could you post the code that handles the notifications on the central side?

[ilockit_CFR]

Hi,

here are the corresponding parts of the central code:

 

static uint8_t on_received(struct bt_conn *conn,
			struct bt_gatt_subscribe_params *params,
			const void *data, uint16_t length)
{
	struct bt_ili_client *ili;

	/* Retrieve ILI Client module context. */
	ili = CONTAINER_OF(params, struct bt_ili_client, mode_notif_params);

	LOG_DBG("[NOTIFICATION] data %p length %u", data, length);
	
	if (!data) {
		LOG_DBG("[UNSUBSCRIBED]");
		params->value_handle = 0;
		atomic_clear_bit(&ili->state, ILI_C_MODE_NOTIF_ENABLED);
		if (ili->cb.unsubscribed) {
			ili->cb.unsubscribed(ili);
		}
		return BT_GATT_ITER_STOP;
	}

	
	if (ili->cb.received) {
		return ili->cb.received(ili, data, length);
	}

	return BT_GATT_ITER_CONTINUE;
}

int bt_ili_client_init(struct bt_ili_client *ili_c,
		       const struct bt_ili_client_init_param *ili_c_init)
{
	if (!ili_c || !ili_c_init) {
		return -EINVAL;
	}

	if (atomic_test_and_set_bit(&ili_c->state, ILI_C_INITIALIZED)) {
		return -EALREADY;
	}

	memcpy(&ili_c->cb, &ili_c_init->cb, sizeof(ili_c->cb));

	return 0;
}

int bt_ili_handles_assign(struct bt_gatt_dm *dm,
			  struct bt_ili_client *ili_c)
{
	const struct bt_gatt_dm_attr *gatt_service_attr =
			bt_gatt_dm_service_get(dm);
	const struct bt_gatt_service_val *gatt_service =
			bt_gatt_dm_attr_service_val(gatt_service_attr);
	const struct bt_gatt_dm_attr *gatt_chrc;
	const struct bt_gatt_dm_attr *gatt_desc;

	if (bt_uuid_cmp(gatt_service->uuid, BT_UUID_ILI_C_SERVICE)) {
		return -ENOTSUP;
	}
	LOG_DBG("Getting handles from service.");
	memset(&ili_c->handles, 0xFF, sizeof(ili_c->handles));

	/* ILI mode Characteristic */
	gatt_chrc = bt_gatt_dm_char_by_uuid(dm, BT_UUID_ILI_C_MODE);
	if (!gatt_chrc) {
		LOG_ERR("Missing mode characteristic.");
		return -EINVAL;
	}
	/* ILI mode Characteristic */
	gatt_desc = bt_gatt_dm_desc_by_uuid(dm, gatt_chrc, BT_UUID_ILI_C_MODE);
	if (!gatt_desc) {
		LOG_ERR("Missing mode value descriptor in characteristic.");
		return -EINVAL;
	}
	LOG_DBG("Found handle for mode characteristic.");
	ili_c->handles.mode = gatt_desc->handle;
	/* ILI mode CCC */
	gatt_desc = bt_gatt_dm_desc_by_uuid(dm, gatt_chrc, BT_UUID_GATT_CCC);
	if (!gatt_desc) {
		LOG_ERR("Missing mode CCC in characteristic.");
		return -EINVAL;
	}
	LOG_DBG("Found handle for CCC of mode characteristic.");
	ili_c->handles.mode_ccc = gatt_desc->handle;

	/* serial Characteristic */
	gatt_chrc = bt_gatt_dm_char_by_uuid(dm, BT_UUID_ILI_C_SERIAL);
	if (!gatt_chrc) {
		LOG_ERR("Missing serial characteristic.");
		return -EINVAL;
	}
	/* ILI serial */
	gatt_desc = bt_gatt_dm_desc_by_uuid(dm, gatt_chrc, BT_UUID_ILI_C_SERIAL);
	if (!gatt_desc) {
		LOG_ERR("Missing serial value descriptor in characteristic.");
		return -EINVAL;
	}
	LOG_DBG("Found handle for serial characteristic.");
	ili_c->handles.serial = gatt_desc->handle;

	/* Assign connection instance. */
	ili_c->conn = bt_gatt_dm_conn_get(dm);
	return 0;
}

int bt_ili_subscribe_mode(struct bt_ili_client *ili_c)
{
	int err;

	if (atomic_test_and_set_bit(&ili_c->state, ILI_C_MODE_NOTIF_ENABLED)) {
		return -EALREADY;
	}

	ili_c->mode_notif_params.notify = on_received;
	ili_c->mode_notif_params.value = BT_GATT_CCC_NOTIFY;
	ili_c->mode_notif_params.value_handle = ili_c->handles.mode;
	ili_c->mode_notif_params.ccc_handle = ili_c->handles.mode_ccc;
	atomic_set_bit(ili_c->mode_notif_params.flags,
		       BT_GATT_SUBSCRIBE_FLAG_VOLATILE);

	err = bt_gatt_subscribe(ili_c->conn, &ili_c->mode_notif_params);
	if (err) {
		LOG_ERR("Subscribe to mode characteristic failed (err %d)", err);
		atomic_clear_bit(&ili_c->state, ILI_C_MODE_NOTIF_ENABLED);
	} else {
		LOG_DBG("[SUBSCRIBED] mode characteristic");
	}

	return err;
}

And here is the part where I subscribe the characteristic in my application:

static void discovery_completed_cb(struct bt_gatt_dm *dm,
				   void *context)
{
	int err;

	LOG_DBG("The discovery procedure succeeded");

	bt_gatt_dm_data_print(dm);

	err = bt_ili_handles_assign(dm, &m_ili_fob);
	if (err) {
		LOG_DBG("Could not init BAS client object, error: %d", err);
	}

    err = bt_ili_subscribe_mode(&m_ili_fob);
	if (err) {
		LOG_DBG("Cannot subscribe to ILI mode value notification "
			"(err: %d)", err);
		/* Continue anyway */
	}
	
	err = bt_gatt_dm_data_release(dm);
	if (err) {
		LOG_DBG("Could not release the discovery data, error "
		       "code: %d", err);
	}
}

[Turbo J]

And there is the location for your BT_GATT_ITER_STOP return value, passed from from the callback function:

      return BT_GATT_ITER_STOP;
	}

	
	if (ili->cb.received) {
	/** vvvvvv--- BT_GATT_ITER_STOP value is ZERO     **/
		return ili->cb.received(ili, data, length);
	}

	return BT_GATT_ITER_CONTINUE;

Pretty sure that your callback function returns zero, which is the value of BT_GATT_ITER_STOP. Try putting a LOG_DBG statement in there.

[ilockit_CFR]

Indeed, there was a path in the callback which returned zero. Now, everything works as expected. 

Thanks for the support.