Communicate two microcontrollers via BLE

[msu7xi]

Hello,

I'm using a nRF52 DK to test BLE communication with another microcontroller. What I need to test is the nRF52 pairing with another brand microcontroller, send a data stream and close the connection.

Could you please tell me which example from the Bluetooth samples list I can use for starting?

Thanks for your attention.

Regards,

[haakonsh]

The Bluetooth: Central / Heart-rate Monitor sample should be a good start.

[msu7xi]

Hello haakonsh,

Thank you very much. I've reviewed this example and it is supposed to connect with the first device with an strong signal. Is there a way to force the board to connect with the device with a given MAC address?

[haakonsh]

Where do you set 'nus_client.conn' to point to the connection object of the ESP32 connection?

[msu7xi]

I am not sure which function should set 'nus_client.conn'. Where is this set in the "central_uart" example? I am using this example as template to modify.

[haakonsh]

This is explained in https://academy.nordicsemi.com/lessons/lesson-3-bluetooth-le-connections/ 

[msu7xi]

Excuse me but this is not clear to me. There is no use of NUS library in lesson 3.

haakonsh said:

Where do you set 'nus_client.conn' to point to the connection object of the ESP32 connection?

Do you mean implementing the callback functions?

/* STEP 2.2 - Implement the callback functions */
void on_connected(struct bt_conn *conn, uint8_t err)
{
    if (err) {
        LOG_ERR("Connection error %d", err);
        return;
    }
    LOG_INF("Connected");
    my_conn = bt_conn_ref(conn);

	/* STEP 3.2  Turn the connection status LED on */
    dk_set_led(CONNECTION_STATUS_LED, 1);
}

void on_disconnected(struct bt_conn *conn, uint8_t reason)
{
    LOG_INF("Disconnected. Reason %d", reason);
    bt_conn_unref(my_conn);

	/* STEP 3.3  Turn the connection status LED off */
    dk_set_led(CONNECTION_STATUS_LED, 0);
}

/* STEP 2.1 - Declare the connection_callback structure */
struct bt_conn_cb connection_callbacks = {
    .connected              = on_connected,
    .disconnected           = on_disconnected,
};

[haakonsh]

I made a mistake, I forgot you are operating as the central and the process is a bit different. 

The connection instance object is set in the function 'bt_nus_handles_assign' in nrf\subsys\bluetooth\services\nus_client.c:168

	/* Assign connection instance. */
	nus_c->conn = bt_gatt_dm_conn_get(dm);

The GATT Discovery Manager is run after a connection has been established in order to read a connected peripheral's GATT services and characteristics. In the NUS client sample this library is used to identify whether the connected peripheral has a NUS service, and to store a given connection instance object if it does.

[msu7xi]

Unknown said:

This time the 'bt_nus_client_send' function returns the -128 error as the nRF52 cannot connect to the ESP32. is there something missing in how I have configured the filtering function?

Right now I cannot establish a connection with the ESP32. Is there anything wrong with the configuration I've set for the filter?

[haakonsh]

Enable debug logs for the nrf_bt_scan module and verify that you are using the correct address. I'm suspecting that you are using the wrong byte-order or endianess. 

It might also be the use of the 'match_all' flag when only one filter is used. 

[msu7xi]

I can establish the connection but after some seconds the microcontroller resets:

Connected: 60:55:F9:F5:29:D2 (public)
Pairing failed conn: 60:55:F9:F5:29:D2 (public), reason 9
Service discovery completed
ASSERTION FAIL [conn] @ WEST_TOPDIR/zephyr/subsys/bluetooth/host/gatt.c:5034
        invalid parameters

*** Booting Zephyr OS build v3.2.99-ncs2 ***

If I add the line for sending data over NUS (call to 'bt_nus_client_send' function) it fails with -128 error.

[haakonsh]

1. The ble peer failed pairing.
   
   
2.  /zephyr/subsys/bluetooth/host/gatt.c:5034: "__ASSERT(conn, "invalid parameters\n");"
   
   What means that bt_gatt_subscribe was not called with a valid connection object. This can be a consequential error due to the failed pairing attempt. 

[msu7xi]

I have added a call to the 'bt_gatt_dm_conn_get' function in the 'discovery_complete' function as follows:

static void discovery_complete(struct bt_gatt_dm *dm,
			       void *context)
{
	struct bt_nus_client *nus = context;
	LOG_INF("Service discovery completed");
	printk("Service discovery completed\n");

	bt_gatt_dm_data_print(dm);

	/* Assign connection instance. */
	nus_client.conn = bt_gatt_dm_conn_get(dm);

	bt_nus_handles_assign(dm, nus);
	bt_nus_subscribe_receive(nus);

	bt_gatt_dm_data_release(dm);
}

This way the microcontroller doesn't reset anymore. Nevertheless, the pairing still fails:

Starting Bluetooth Central UART example
scan err: 0
Scanning
Scanning successfully started
connected conn_err: 0
Connected: 60:55:F9:F5:29:D2 (public)
Pairing failed conn: 60:55:F9:F5:29:D2 (public), reason 9
Service discovery completed

How can I solve this problem?