Definition of a different UUID for a characteristic

[Marlene]

Hi,

I want my characteristic to have a different UUID than its service on my server:

I followed the leads from the post below:

https://devzone.nordicsemi.com/f/nordic-q-a/15208/characteristic-s-base-uuid-different-from-service-s-base-uuid

Below is my function to add a characteristic to the service:

static uint32_t setting_zone_power_char_add(ble_cooktop_t * p_cooktop, const ble_cooktop_init_t * p_cooktop_init)
{
    
    ble_gatts_char_md_t char_md;
    ble_gatts_attr_t    attr_char_value;
    ble_gatts_attr_md_t attr_md;


    ble_uuid_t uuidA = { .uuid = 0x6666 };
    ble_uuid128_t uuidA_base = { 0xAA, 0xAA, 0xAA, 0xAA, 
										0xAA, 0xAA, 0x99, 0x99, 
										0x88, 0x88, 0x77, 0x77, 
										0x00, 0x00, 0x66, 0x66 };
    sd_ble_uuid_vs_add(&uuidA_base, &uuidA.type);
    // uuidA is now 66666666-7777-8888-9999-AAAAAAAAAAAA

    memset(&char_md, 0, sizeof(char_md));

    static char user_desc[] = "setting_zone";
    char_md.p_char_user_desc  = (uint8_t *) user_desc;
    char_md.char_user_desc_size = strlen(user_desc);
    char_md.char_user_desc_max_size = strlen(user_desc);	

    char_md.char_props.write         = 1;
    char_md.char_props.read         = 1;
    char_md.char_props.notify         = 1;
    char_md.char_props.indicate         = 1;
    char_md.char_props.write_wo_resp = 1;
    char_md.p_char_user_desc         = NULL;
    char_md.p_char_pf                = NULL;
    char_md.p_cccd_md                = NULL;
    char_md.p_sccd_md                = NULL;

       uuidA.type = BLE_UUID_TYPE_VENDOR_BEGIN;

    memset(&attr_md, 0, sizeof(attr_md));

    BLE_GAP_CONN_SEC_MODE_SET_OPEN(&attr_md.read_perm);
    BLE_GAP_CONN_SEC_MODE_SET_OPEN(&attr_md.write_perm);

    attr_md.vloc    = BLE_GATTS_VLOC_STACK;
    attr_md.rd_auth = 0;
    attr_md.wr_auth = 0;
    attr_md.vlen    = 1;

    memset(&attr_char_value, 0, sizeof(attr_char_value));

    attr_char_value.p_uuid    = &uuidA;
    attr_char_value.p_attr_md = &attr_md;
    attr_char_value.init_len  = 1;
    attr_char_value.init_offs = 0;

    attr_char_value.max_len   = 0x03;

    //sd_ble_gatts_descriptor_add();
    return sd_ble_gatts_characteristic_add(p_cooktop->service_handle,
                                           &char_md,
                                           &attr_char_value,
                                           &p_cooktop->setting_zone_power_handles);


}

The project compiles and I can connect to my server using nrfConnect but the UUID for the characteristic is not the one I defined but used the same base UUID as the service UUID.

[Marlene]

Hi,

Any news on my topic?

Regards, Marlene

[Mttrinh]

Hi,

It seems to be correct. Can you try increasing the UUID count? What are you using to see if the base UUID has changed? Can you try with nRF Connect Desktop and see if it has changed?

[Andy]

Your problem is this line. Remove it.

uuidA.type = BLE_UUID_TYPE_VENDOR_BEGIN;

I recently helped another user with this and he was still seeing the wrong UUID. It was solved by turning his phone off and on again. iOS caches BLE services and characteristics and apparently Android does too. They get cleared when you turn on airplane mode or when you reboot your phone.