I have a question about configuration of charateristic value R/W permission.

[JoonDong]

I saw following code configuring about permission of charateristic value R/W.

it's in uart example of SDK 11.0.0.

static uint32_t tx_char_add (ble_nus_t * p_nus, const ble_nus_init_t * p_nus_init){
   ...
   BLE_GAP_CONN_SEC_MODE_SET_OPEN(&attr_md.read_perm);
   BLE_GAP_CONN_SEC_MODE_SET_OPEN(&attr_md.write_perm);
   ...
}

it was not a setting about whether R/W is possible or not.

So, is it the setting about connection security mode that R/W is possible?

[AmiguelS]

You may find this tutorial useful, more specifically Step 2.F. The following code configures a characteristic to allow Read and Notify but reject Write.

void ble_add_char(){
    ...

    //Add Characteristics to stack
    ble_gatts_char_md_t char_md;

    memset(&char_md, 0, sizeof(char_md));
    char_md.char_props.write_wo_resp  = 0;
    char_md.char_props.write  = 0;
    char_md.char_props.read   = 1;
    char_md.char_props.notify = 1;

    ...

    //Add Characteristic to stack
    sd_ble_gatts_characteristic_add(service, &char_md, &attr_char_value, handle);
}

[JoonDong]

Finally, does it mean that R/W availability and R/W permission should be separated?

[JoonDong]

And I can't find out the setting about R/W availability of Characteristic's components(characteristic value attribute, cccd and so on.. )

does Characteristic's R/W availability automatically apply to Characteristic's components?

[JoonDong]

But should cccd be set to Write and Notify?

[FormerMember]

Yes, part of the security for a device can be to limit the read/write properties.

attr_md sets the actual properties for a characteristic (the actual accessibility). char_md sets the properties that will be found during service discovery. For the properties to be in conformance with the Bluetooth Spec, the attr_md properties and the char_md properties should be the same.

Update March 17th 2017:

When adding a characteristic, both characteristic metadata and attribute metatdata should be set. As stated in the documentation for the characteristic metatdata --> characteristic properties (ble_gatts_char_md_t --> ble_gatt_char_props_t), it is only the properties of the characteristic.

The attribute metadata (ble_gatts_attr_md_t) contains the actual permissions.