nrf51822 --- 特征值添加描述

1.目的

   给串口的2个特征值加上描述

2.分析

   很多时候，我们定义特征值的时候，都希望一目了然，知道这个特征值干什么的，这里我们来介绍给特征值加上描述符，这样一看描述就知道这个特征值做什么的了

3.平台：

协议栈版本：SDK10.0.0

编译软件：keil 5.14

硬件平台：nrf51822最小系统

例子：SDK 10.0.0\examples\ble_peripheral\ble_app_uart\pca10028\s110\arm4

4.步骤

 在这里，我们把串口发送服务，添加描述符为 “Tx”

                         串口接收服务，添加描述符为“Rx”

static uint32_t tx_char_add(ble_nus_t * p_nus, const ble_nus_init_t * p_nus_init)
{
    ble_gatts_char_md_t char_md;
    ble_gatts_attr_t    attr_char_value;
    ble_uuid_t          ble_uuid;
    ble_gatts_attr_md_t attr_md;
    char tx_desc[] = "Tx" ;  //添加代码1
	
    memset(&char_md, 0, sizeof(char_md));

	  char_md.p_char_user_desc  = (uint8_t *)tx_desc ; //添加代码2
		char_md.char_user_desc_size = strlen(tx_desc);//添加代码3
	  char_md.char_user_desc_max_size =strlen(tx_desc);//添加代码4
	
    char_md.char_props.write         = 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_user_desc_md           = NULL;
    char_md.p_cccd_md                = NULL;
    char_md.p_sccd_md                = NULL;
   ble_uuid.type = p_nus->uuid_type;
    ble_uuid.uuid = BLE_UUID_NUS_TX_CHARACTERISTIC;

    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    = &ble_uuid;
    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   = BLE_NUS_MAX_TX_CHAR_LEN;

    return sd_ble_gatts_characteristic_add(p_nus->service_handle,
                                           &char_md,
                                           &attr_char_value,
                                           &p_nus->tx_handles);
}

static uint32_t rx_char_add(ble_nus_t * p_nus, const ble_nus_init_t * p_nus_init)
{
    /**@snippet [Adding proprietary characteristic to S110 SoftDevice] */
    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;
    char rx_desc[] = "Rx" ;   //添加代码1
	
    memset(&cccd_md, 0, sizeof(cccd_md));

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

    cccd_md.vloc = BLE_GATTS_VLOC_STACK;

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

    char_md.char_props.notify = 1;
  char_md.p_char_user_desc  = (uint8_t *)rx_desc ;  //添加代码2
		char_md.char_user_desc_size = strlen(rx_desc);//添加代码3
	  char_md.char_user_desc_max_size =strlen(rx_desc);//添加代码4
		
    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_nus->uuid_type;
    ble_uuid.uuid = BLE_UUID_NUS_RX_CHARACTERISTIC;

    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    = &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_NUS_MAX_RX_CHAR_LEN;

    return sd_ble_gatts_characteristic_add(p_nus->service_handle,
                                           &char_md,
                                           &attr_char_value,
                                           &p_nus->rx_handles);
    /**@snippet [Adding proprietary characteristic to S110 SoftDevice] */
}

编译代码 downloda to the board！！！

用lightbule看结果：

  

是不是成功了呀！！！！其他的也是如此修改。。。。。。

疑问：这个描述有什么限制呢??比如长度？？