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);

[Hung Bui]

:

1. No. Why you talk about GATT client here? we are talking about gatt server.

2. It should as it's defined in BLE_GATTS_VAR_ATTR_LEN_MAX isn't it.

3. "The Client Characteristic Configuration declaration shall be readable and writable." It's defined in the spec (section 3.3.3.3 Vol 3 Part G Spec v4.0)

4. I don't understand you. Authorization has nothing to do with long read. Have you looked at the sequence chart I mentioned in the answer ??

5. Check the message sequence chart.

6. You mean sd_ble_gatts_value_set? This function tells nothing to the peer device, it only update the value of the characteristic. You need to send a notification if you want to tell the peer device you have new data (using sd_ble_gatts_hvx() function). This function take a pointer and length and then update it to the buffer you declare when you initialize the characteristic. The buffer can be inside the stack if you use BLE_GATTS_VLOC_STACK. If you use BLE_GATTS_VLOC_USER, the it will be the buffer you provided as the initialize value of the characteristic.