Filtering based on 128 bit uuid using whitelist

[Ignacio]

Hi there,

@Simonr, I need further help on this case 

https://devzone.nordicsemi.com/f/nordic-q-a/58464/filtering-based-on-128-bit-uuid

It is said that it is possible to use " a whitelist that holds the UUIDs you want to scan in order to filter these beacons".

To add these UUIDs to the whitelist it recommends to use sd_ble_gap_whitelist_set. However this funtion only accepts a list of the ble_gap_addr_t structure.

This structure is defined as follows:

uint8_t addr_id_peer: 1

uint8_t addr_type: 7

uint8_t addr [(6)]

I dont's see the way to fit a 128-bit UUID there. So, the question remains. Is it possible to filter scan packages using a 128-bit UUID? If yes, how?

Thanks!

[Simonr]

Hi

Right, there are some modifications necessary to hold and store 128-bit UUIDs. Here's a quick mock-up on how you can do it on the central end (please note that this is not a full example, and just a snippet of code to be added to an existing central project):

/* Two-dimensional array to hold the UUIDs that should be "whitelisted" */
uint8_t whitelist[30][16] = {0};

/*NRF FSTORAGE instance*/
NRF_FSTORAGE_DEF(nrf_fstorage_t whitelist_storage) =
{
    /* Set a handler for fstorage events. */
    .evt_handler = fstorage_evt_handler,
    .start_addr = 0x3e000,
    .end_addr   = 0x3ffff,
};  

/*Function for reading UUIDs from flash and putting them in whitelist on start-up*/
static void read_flash(void)
{
    ret_code_t err_code;
    /*Read flash at the address where uuid_number is stored*/
    err_code = nrf_fstorage_read(&whitelist_storage, 0x3e000, &uuid_number, 4);
    APP_ERROR_CHECK(err_code);

    /*If nothing has previously been written to flash, uuid_number will equal 255*/
    if(uuid_number == 255)
    {
        uuid_number = 0;
    }
    else
    {
        /*Read out as many UUIDs as indicated by uuid_number*/
        for(uint8_t i = 0; i < uuid_number; i++)
        {
            nrf_fstorage_read(&whitelist_storage, flash_addr, &whitelist[i], 16);
            flash_addr += 0x10;
        }
    } 
}

int main(void)
{
    ret_code_t rc;
    
    /*Initiate the fstorage instance*/
    rc = nrf_fstorage_init(&whitelist_storage, &nrf_fstorage_sd, NULL);
    APP_ERROR_CHECK(rc);
}

Best regards,

Simon

[Ignacio]

Many thanks. Is it possible to do any modifications on the filters' side instead of the whitelist? Is that snippet portable to the latest nRF Connect SDK?

[Simonr]

The filter can't be changed to support 128 bit as that is not a filter option by default. The snippet was part of a student project once upon a time that used the nRF5 SDK, so some changes will be necessary to make it work on the nRFConnect SDK.

Best regards,

Simon