低功耗蓝牙4.0BLE编程-nrf51822开发(10)-描述符

特性中的属性有两种：属性值或描述符。

支持通知或指示的特性中默认有一个描述符：客户端特性配置描述符(Client Characteristic Configuration Descriptor，CCCD)。它的UUID是0x2902。

添加描述符的函数是：

uint32_t sd_ble_gatts_descriptor_add  ( uint16_t  char_handle,
  ble_gatts_attr_t const *const  p_attr,
  uint16_t *const  p_handle
 )  

Parameters

[in]	char_handle	Handle of the characteristic where the descriptor is to be placed, if BLE_GATT_HANDLE_INVALID is used, it will be placed sequentially.
[in]	p_attr	Pointer to the attribute structure.
[out]	p_handle	Pointer to a 16-bit word where the assigned handle will be stored.

示例代码：

BLE_UUID_BLE_ASSIGN(ble_uuid, BLE_UUID_REPORT_REF_DESCR);  
 
memset(&attr_md, , sizeof(attr_md));  
 
attr_md.read_perm = p_bas_init->battery_level_report_read_perm;
BLE_GAP_CONN_SEC_MODE_SET_NO_ACCESS(&attr_md.write_perm);  
 
attr_md.vloc       = BLE_GATTS_VLOC_STACK;
attr_md.rd_auth    = ;
attr_md.wr_auth    = ;
attr_md.vlen       = ;  
 
init_len = ble_srv_report_ref_encode(encoded_report_ref, p_bas_init->p_report_ref);  
 
memset(&attr_char_value, , sizeof(attr_char_value));  
 
attr_char_value.p_uuid       = &ble_uuid;
attr_char_value.p_attr_md    = &attr_md;
attr_char_value.init_len     = init_len;
attr_char_value.init_offs    = ;
attr_char_value.max_len      = attr_char_value.init_len;
attr_char_value.p_value      = encoded_report_ref;  
 
err_code = sd_ble_gatts_descriptor_add(p_bas->battery_level_handles.value_handle,
                                       &attr_char_value,
                                       &p_bas->report_ref_handle);
if (err_code != NRF_SUCCESS)
{
    return err_code;
}