Modify ble_app_uart_c example to scan for custom UUID not working

[EricDelangis]

I am trying to do the same thing that others have tried in the past, and that is to modify the ble_app_uart_c example to connect to our custom peripheral device.

I have gone through several blog posts regarding this issue, including: https://devzone.nordicsemi.com/f/nordic-q-a/20641/how-to-use-ble_app_uart_c-for-custom-uuid-service/80467#80467 and https://devzone.nordicsemi.com/f/nordic-q-a/12555/ble-central-custom-uuid and https://devzone.nordicsemi.com/f/nordic-q-a/44912/scan-filters-for-custom-uuid-is-not-matching and many others.  Unfortunately, I haven't been able to get a connection.  The code is failing the adv_uuid_compare function nrf_ble_scan_c. 

The changes that I made were to ble_nus_c are:

#define NUS_BASE_UUID {{0xFB, 0x34, 0x9B, 0x5F, 0x80, 0x00, 0x00, 0x80, 0x00, 0x10, 0x00, 0x00, 0xF0, 0xFF, 0x00, 0x00}} /**< Used vendor specific UUID. */  

(Note: The custom UUID is: 0000fff0-0000-1000-8000-00805f9b34fb). 

Made changes to the service/characteristics as well.  Note that 

#define BLE_UUID_NUS_SERVICE 0xFFF0                          /**< The UUID of the Nordic UART Service. */

(Note: We don't have a comparable service for the NUS 0001 so changed it to the FFF0 to match the main UUID).

#define BLE_UUID_NUS_RX_CHARACTERISTIC 0xFFF1   /**< The UUID of the RX Characteristic. */

#define BLE_UUID_NUS_TX_CHARACTERISTIC 0xFFF2   /**< The UUID of the TX Characteristic. */

I verified that the all_filters_mode is false so it should only match one UUID.

I added printf statements to nrf_ble_scan_c file to display the comparison values:

#if (NRF_BLE_SCAN_UUID_CNT > 0)
/**@brief Function for comparing the provided UUID with the UUID in the advertisement packets.
*
* @param[in] p_adv_report Advertising data to parse.
* @param[in] p_scan_ctx Pointer to the Scanning Module instance.
*
* @return True if the UUIDs match. False otherwise.
*/
static bool adv_uuid_compare(ble_gap_evt_adv_report_t const * const p_adv_report,
nrf_ble_scan_t const * const p_scan_ctx)
{

// Print out the compare values:
printf("p_adv_report value is: %x \r\n",p_adv_report);
printf("p_scan_ctx is: %x \r\n", p_scan_ctx);
printf("\r\n\r\n");

nrf_ble_scan_uuid_filter_t const * p_uuid_filter = &p_scan_ctx->scan_filters.uuid_filter;

bool const all_filters_mode = p_scan_ctx->scan_filters.all_filters_mode;
uint8_t const counter =
p_scan_ctx->scan_filters.uuid_filter.uuid_cnt;
uint8_t index;
uint16_t data_len;
uint8_t uuid_match_cnt = 0;

data_len = p_adv_report->data.len;

for (index = 0; index < counter; index++)
{

//printf("Entering UUID Compare function in nrf_ble_scan.c.\r\n");  (Note: We do get here.)

if (ble_advdata_uuid_find(p_adv_report->data.p_data,
data_len,
&p_uuid_filter->uuid[index]))

{

printf("If we got here then the UUID should have matched.\r\n");   (Note: We do not get here.)

uuid_match_cnt++;

// In the normal filter mode, only one UUID is needed to match.
if (!all_filters_mode)
{
break;
}
}
else if (all_filters_mode)
{
break;
}
else
{
// Do nothing.
}
}

// In the multifilter mode, all UUIDs must be found in the advertisement packets.
if ((all_filters_mode && (uuid_match_cnt == counter)) ||
((!all_filters_mode) && (uuid_match_cnt > 0)))
{
return true;
}

return false;
}

The compare values from successive scans are:  

p_adv_report value is: 2000fd1c

p_scan_ctx is: 20003684

p_adv_report value is: 2000fcec

p_scan_ctx is: 20003684

Clearly since the values are not the same, they won't match but I can't figure out where these values are coming from.  Also, why aren't the full 218 bits being displayed and compared?

Please advise.

[Vidar Berg]

Hi,

Is there any way you can change the service UUID on the Peripheral/Server? It's using the Bluetooth SIGs base UUID: https://www.bluetooth.com/specifications/assigned-numbers/service-discovery/ which is not allowed for custom services. In any case, I think it will work if you change the uuid.type from NUS_SERVICE_UUID_TYPE to BLE_UUID_TYPE_BLE in main.c

[EricDelangis]

Hi Vidar, 

No such luck.  Made changes in two places:

Line 72 - #define BLE_UUID_TYPE_BLE BLE_UUID_TYPE_VENDOR_BEGIN /**< UUID type for the Nordic UART Service (vendor specific). */

Line 88 - 

/**@brief NUS UUID. */
static ble_uuid_t const m_nus_uuid =
{
.uuid = BLE_UUID_NUS_SERVICE,
.type = BLE_UUID_TYPE_BLE
};

No apparent change.  Unfortunately, it will be difficult to change the Peripheral UUID since we don't have the ability to modify that code.  We will need to find a work around on our end.

Thanks,

[Vidar Berg]

Hi,

Maybe you have done it already, but I would suggest inspecting the advertising packet from the peripheral in nRF connect on Android/iOS and check whether it's advertising the full 128-bit UUID or just the 16-bit Service UUID. I find it a bit strange that it's using the SIG base UUID for a custom service. 

[EricDelangis]

OK, I'll check that out.  In the meantime, I've been somewhat successful in matching the "Full Name" and getting to:

        static void on_connected_evt(nrf_ble_gatt_t * p_gatt, ble_evt_t const * p_ble_evt) 

I haven't traced it past this point yet but the nRF52 DK seems to time out and restarts the scan function before the connection can be completed.

Assuming that they are only broadcasting the 16bit UUID, what function do I call to match it?  Do I need to set up any other variables to make that work?