Enabling notifications from custom UUID as central

[pbirkner]

I am trying to receive ble notifications from a custom UUID as a central device and then relay that information to my computer via ble. I have been following the nordic relay example and have been mostly successful. I run into problems when I try and connect to a custom UUID. The problem is that custom service starts at the FIRST index of the 128 bit UUID rather than the second. I have been following the ble_nus_c.c program to get this working with no luck. Here is my relevant code to initialize the service:

uint32_t ble_nus_c_init(ble_nus_c_t * p_ble_nus_c, ble_nus_c_init_t * p_ble_nus_c_init)
{
uint32_t      err_code;
ble_uuid_t    uart_uuid;
ble_uuid128_t nus_base_uuid = CUST_BASE_UUID;

VERIFY_PARAM_NOT_NULL(p_ble_nus_c);
VERIFY_PARAM_NOT_NULL(p_ble_nus_c_init);

p_ble_nus_c->uuid_type = 0x01;    //service starts here rather than 0x02


err_code = sd_ble_uuid_vs_add(&nus_base_uuid, &p_ble_nus_c->uuid_type);
VERIFY_SUCCESS(err_code);


uart_uuid.type = p_ble_nus_c->uuid_type;
uart_uuid.uuid = BLE_UUID_NUS_SERVICE;

p_ble_nus_c->conn_handle           = BLE_CONN_HANDLE_INVALID;
p_ble_nus_c->evt_handler           = p_ble_nus_c_init->evt_handler;
p_ble_nus_c->handles.nus_rx_handle = BLE_GATT_HANDLE_INVALID;
p_ble_nus_c->handles.nus_tx_handle = BLE_GATT_HANDLE_INVALID;

return ble_db_discovery_evt_register(&uart_uuid);
}

and here is the code to discover the characteristic and enable notifications:

void ble_nus_c_on_db_disc_evt(ble_nus_c_t * p_ble_nus_c, ble_db_discovery_evt_t * p_evt)
{
ble_nus_c_evt_t nus_c_evt;

memset(&nus_c_evt,0,sizeof(ble_nus_c_evt_t));
ble_gatt_db_char_t * p_chars = p_evt->params.discovered_db.charateristics;



// Check if the NUS was discovered.
if (p_evt->evt_type == BLE_DB_DISCOVERY_COMPLETE &&

    p_evt->params.discovered_db.srv_uuid.uuid == CUST_BASE_UUID &&
    p_evt->params.discovered_db.srv_uuid.type ==  p_ble_nus_c->uuid_type)
{
    uint32_t i;

    for (i = 0; i < p_evt->params.discovered_db.char_count; i++)
    {
        switch (p_chars[i].characteristic.uuid.uuid)
        {

            case BLE_UUID_NUS_TX_CHARACTERISTIC:

                nus_c_evt.handles.nus_tx_handle = p_chars[i].characteristic.handle_value;
                break;

            case BLE_UUID_CUST_CHARACTERISTIC:

                nus_c_evt.handles.nus_rx_handle = p_chars[i].characteristic.handle_value;
                nus_c_evt.handles.nus_rx_cccd_handle = p_chars[i].cccd_handle;
                break;

            default:
                break;
        }
   }

    if (p_ble_nus_c->evt_handler != NULL)
    {

        nus_c_evt.conn_handle = p_evt->conn_handle;
        nus_c_evt.evt_type    = BLE_NUS_C_EVT_DISCOVERY_COMPLETE;
        p_ble_nus_c->evt_handler(p_ble_nus_c, &nus_c_evt);
    }

}

[Petter Myhre]

The problem is that custom service starts at the FIRST index of the 128 bit UUID rather than the second.

I don't quite understand what you mean by this. Could you elaborate? You are able to connect? But not discover the service? What happens?

(Not relevant, but why are you doing p_ble_nus_c->uuid_type = 0x01;?)

[pbirkner]

I am able to connect to the device. It also has a heart rate service, which I am able to discover. I am not able to discover the service with a custom UUID. I believe my issue stems from the fact that their custom service starts at the 0x01 index of their custom UUID rather than the 0x02 index. This is why I explicitly state: p_ble_nus_c->uuid_type = 0x01.

[Petter Myhre]

You can't use 0x01 for custom UUIDs. And it doesn't make sense to set it to 0x01. The argument UUID type argument to sd_ble_uuid_vs_add() is an output, not an output. You should add your custom UUID base and use the outputted UUID type as a reference to that base.

@param[out] p_uuid_type  Pointer to a uint8_t where the type field in @ref ble_uuid_t corresponding to this UUID will be stored.

[pbirkner]

"You should add your custom UUID base and use the outputted UUID type as a reference to that base"

How do I do this?

[Petter Myhre]

You add a UUID base by calling sd_ble_uuid_vs_add(). After you have called it, the UUID type or UUID base reference will be found in uuid_type.