Adding characteristic (for purpose of long read) fails

[Aurabindo]

I've added a custom service for transferring data. It shall contain one characteristic that will notify when data is available, and the other should be a long read characteristic (no notify). sd_ble_gatts_characteristic_add is failing (return 0x7) when I add the second characteristic.

I've made attr_char_value.max_len to 512. I am enabling attr_md.rd_auth = 1 to handle the long read as mentioned in the post devzone.nordicsemi.com/.../

Is this the right way, or are there any new preferred way to enable long read ?

Could someone please point out what is the invalid parameter ? I'm using sdk 14.1 with GCC compiler. The code is below:

static uint32_t sensor_data_char_add(ble_ksh_t * p_ksh, ble_ksh_init_t const * p_pke_init) {
ble_gatts_char_md_t char_md;
ble_gatts_attr_md_t cccd_md;
ble_gatts_attr_t    attr_char_value;
ble_uuid_t          ble_uuid;
ble_gatts_attr_md_t attr_md;

extern uint8_t sensor_data_buffer[BLE_KSH_MAX_DATA_CHAR_LEN];

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

BLE_GAP_CONN_SEC_MODE_SET_OPEN(&cccd_md.read_perm);

cccd_md.vloc = BLE_GATTS_VLOC_STACK;

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

char_md.char_props.read = 1;
char_md.p_char_user_desc  = NULL;
char_md.p_char_pf         = NULL;
char_md.p_user_desc_md    = NULL;
char_md.p_cccd_md         = &cccd_md;
char_md.p_sccd_md         = NULL;

ble_uuid.type = p_ksh->uuid_type;
ble_uuid.uuid = BLE_UUID_KSH_DATA_CHARACTERISTIC;

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

BLE_GAP_CONN_SEC_MODE_SET_OPEN(&attr_md.read_perm);

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

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

attr_char_value.p_uuid    = &ble_uuid;
attr_char_value.p_attr_md = &attr_md;
attr_char_value.init_len  = sizeof(uint8_t);
attr_char_value.init_offs = 0;
attr_char_value.max_len   = BLE_GATTS_VAR_ATTR_LEN_MAX;
attr_char_value.p_value   = &sensor_data_buffer[0];

return sd_ble_gatts_characteristic_add(p_ksh->service_handle,
                                       &char_md,
                                       &attr_char_value,
                                       &p_ksh->data_handles);

}

[Hung Bui]

Hi Aura,

There is no relation between read blob and read with authorization . Have a look here.

The reason you have error #7 is that you don't set a write permission for CCCD which is required. Try adding this:

BLE_GAP_CONN_SEC_MODE_SET_OPEN(&cccd_md.write_perm);

[Aurabindo]

Thank you for the response @Hung Bui, I have some questions:

1. Are there any other setup necessary to do related to GATT Client during initialization?

2. Is the value 512 valid for the max length of the characteristic?

3. I'm unable to understand the reason why cccd needs the write permission, when there is no need for a peer to write to it, since it doesnt support enabling notification. Are there other reasons cccd needs to be written ?