Question about UUID with ble_db_discovery_evt_register()

[John]

I'm developing a central that discovers services in a peripheral.  The services are both custom and standard BLE services.  Discovery is working fine, but there is one issue I'm unsure of:  when calling ble_db_discovery_evt_register, a UUID of type ble_uuid_t is passed as an argument.  When discovering standard services with 16-bit UUIDs, this makes sense, but when discovering custom services with 128-bit UUIDs, what value should be used here?  I'm using sd_ble_uuid_vs_add for the custom services, but I've found that custom services are only discovered when I set the UUID passed to ble_db_discovery_evt_register to 1.

[Simon]

Take a look at the ble_app_uart_c example and the function ble_nus_c_init() in ble_nus_c.c, which illustrates how to use 128-bit UUID's. I've provided the code down below with comments:

// Add a Vendor Specific 128-bit base UUID to the BLE stack table
// p_ble_nus_c->uuid_type will be equal to BLE_UUID_TYPE_VENDOR_BEGIN after the call
err_code = sd_ble_uuid_vs_add(&nus_base_uuid, &p_ble_nus_c->uuid_type);
VERIFY_SUCCESS(err_code);

//Set uart_uuid.type equal to BLE_UUID_TYPE_VENDOR_BEGIN
uart_uuid.type = p_ble_nus_c->uuid_type;
// Set uart_uuid.uuid equal to BLE_UUID_NUS_SERVICE (16 bit UUID), which
// will be equal to byte 12 and 13 of the base UUID set eariler
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->error_handler         = p_ble_nus_c_init->error_handler;
p_ble_nus_c->handles.nus_tx_handle = BLE_GATT_HANDLE_INVALID;
p_ble_nus_c->handles.nus_rx_handle = BLE_GATT_HANDLE_INVALID;
p_ble_nus_c->p_gatt_queue          = p_ble_nus_c_init->p_gatt_queue;

return ble_db_discovery_evt_register(&uart_uuid);

Best regards,

Simon

[John]

// Set uart_uuid.uuid equal to BLE_UUID_NUS_SERVICE (16 bit UUID), which
// will be equal to byte 12 and 13 of the base UUID set eariler
uart_uuid.uuid = BLE_UUID_NUS_SERVICE;

BLE_UUID_NUS_SERVICE is 1, but there is no "1" anywhere in the base UUID (NUS_BASE_UUID), so I still don't understand where the "1" is coming from.

[Simon]

I see now that I explained it poorly, my apologies for that. The BLE_UUID_NUS_SERVICE is not equal to byte 12 and 13 of the base UUID. But the new UUID, which is a combination of BLE_UUID_NUS_SERVICE and the base UUID will be equal to the base UUID with exception of byte 12 and 13, which is equal to BLE_UUID_NUS_SERVICE. 

If you are still confused, read this tutorial (section "Universally Unique ID (UUID)), which explains this in-depth.

Best regards,

Simon

[John]

Now it makes sense, thank you.