smartconfig配置成功后，不能发现设备

官方有一个mDNS的例子，我增加一些备注，可供参考

//*****************************************************************************
//
//! Main function
//!
//! \param None
//!
//! \return None
//!
// In SDK example device is advertising it's IP using mDNS protocol. You need to implement mDNS listener at the other end(mobile or PC) .
// You can easily implement mDNS listener as its very simple protocol. mDNS uses multicast UDP packets.
//
// 1. Create a udp socket on port 5353
// 2. Join muticast group on "224.0.0.251"
// 3. receive packets and parse the data retrieve IP
//
// For more details please go through mDNS RFC(rfc6762).
//
// sl_NetAppMDNSRegisterService()向 224.0.0.251 + 5353广播自己的IP地址和端口号及message
// sl_NetAppDnsGetHostByService()监听224.0.0.251 + 5353地址接收到提供服务的目的IP地址和端口号及message
//*****************************************************************************
static long mDNS_Task()
{
int iretvalmDNS;
long lRetVal = -1;
unsigned char policyVal;
#ifndef MDNS_ADVERTISE
unsigned int pAddr;
unsigned long usPort;
unsigned short ulTextLen = 200;
char cText[200];
int i;
#endif
InitializeAppVariables();
//
// Following function configure the device to default state by cleaning
// the persistent settings stored in NVMEM (viz. connection profiles &
// policies, power policy etc)
//
// Applications may choose to skip this step if the developer is sure
// that the device is in its default state at start of applicaton
//
// Note that all profiles and persistent settings that were done on the
// device will be lost
//
lRetVal = ConfigureSimpleLinkToDefaultState();
if(lRetVal < 0)
{
if (DEVICE_NOT_IN_STATION_MODE == lRetVal)
{
UART_PRINT("Failed to configure the device in its default state\n\r");
}

return -1;
}

UART_PRINT("Device is configured in default state \n\r");

//
// Assumption is that the device is configured in station mode already
// and it is in its default state
//
lRetVal = sl_Start(0, 0, 0);
if (lRetVal < 0 || ROLE_STA != lRetVal)
{
UART_PRINT("Failed to start the device \n\r");
return -1;
}

UART_PRINT("Device started as STATION \n\r");

//powering on the CC3200 device

//reset all policies
sl_WlanPolicySet( SL_POLICY_CONNECTION,
SL_CONNECTION_POLICY(0,0,0,0,0),
&policyVal,
1 /*PolicyValLen*/);

//
//Connecting to WLAN AP
//
lRetVal = WlanConnect();
ASSERT_ON_ERROR(lRetVal);

UART_PRINT("Connection established w/ AP and IP is aquired \n\r");

#ifdef MDNS_ADVERTISE
//Registering for the mDNS service.
iretvalmDNS = sl_NetAppMDNSUnRegisterService(SERVICE_NAME,(unsigned char)strlen(SERVICE_NAME));
// Time To Live(TTL)生存时间(in seconds)，简单的说它表示DNS记录在DNS服务器上缓存时间
// Advertise(Mdns host) 向224.0.0.251 + 5353广播自己的IP地址和端口号及message
//--------------------------------------------------------------------mDNS服务理解---------------------------------------------------------------------------------
// CC3200_A连接AP进入局域网获取自身IP地址，同时开启mDNS服务，并向mDNS服务注册一下信息(sl_NetAppMDNSRegisterService)：我提供SERVICE_NAME服务，我IP:192.168.1.101端口200
// 当CC3200_B连接AP进入局域网，并向CC3200_B的mDNS服务请求(sl_NetAppDnsGetHostByService)，我要找局域网内SERVICE_NAME服务器，CC3200_B的mDNS就会去局域网内向其他的mDNS询问，
// 并且最终告诉你，有一个IP地址为192.168.1.101，端口号是200的主机，也就是CC3200_A提供SERVICE_NAME服务，所以CC3200_B就知道了CC3200_A的IP地址和端口号了。
//-----------------------------------------------------------------------------------------------------------------------------------------------------------------
iretvalmDNS = sl_NetAppMDNSRegisterService(SERVICE_NAME,(unsigned char)strlen(SERVICE_NAME),"Service registered for 3200",\
(unsigned char)strlen("Service registered for 3200"),200,2000,1); //端口号Port=200 + Time To Live(TTL)=2000 + service is unique

if(iretvalmDNS == 0)
{
Report("MDNS Registration successful\n\r");
}
else
{
Report("MDNS Registered failed\n\r");
}
#else
for( i= 0;i<100;i++)
{
iretvalmDNS = 1;
while(iretvalmDNS)
{
ulTextLen = 200;
// listen(Mdns client) 监听224.0.0.251 + 5353地址接收到提供服务的目的IP地址和端口号及message
iretvalmDNS = sl_NetAppDnsGetHostByService(SERVICE_NAME,(unsigned char)strlen(SERVICE_NAME),SL_AF_INET,(unsigned long *)&pAddr,&usPort,&ulTextLen,&cText[0]);
}
if(iretvalmDNS == 0)
{
cText[ulTextLen] = '\0';
Report("\n\rPort: %d\n\r",usPort );
Report("Addr: %d.%d.%d.%d\n\r",SL_IPV4_BYTE(pAddr,3),
SL_IPV4_BYTE(pAddr, 2), SL_IPV4_BYTE(pAddr, 1),
SL_IPV4_BYTE(pAddr, 0));
Report("TLen: %d\n\r",ulTextLen );
Report("Text: %s\n\r",cText );
}

}
#endif
return SUCCESS;
}