单片机SNTP问题

void sendNTPpacket(IPAddress address) {
  memset(packetBuffer, 0, ETHERNET_BUF_MAX_SIZE);
  packetBuffer[0] = 0xE3;  // LI, Version, Mode
  packetBuffer[1] = 0;     // Stratum, or type of clock
  packetBuffer[2] = 6;     // Polling Interval
  packetBuffer[3] = 0xEC;  // Peer Clock Precision
  packetBuffer[12] = 49;
  packetBuffer[13] = 0x4E;
  packetBuffer[14] = 49;
  packetBuffer[15] = 52;
  Udp.beginPacket(address, 123);//NTP requests are to port 123
  Udp.write(packetBuffer, ETHERNET_BUF_MAX_SIZE);
  Udp.endPacket();
}


void loop() {
  delay(1000);
  if (bStr)
  {
    bStr = false;
    sendNTPpacket(IPAddress(198,120,0,100));//10秒执行一次
  }
  if (Udp.parsePacket()) {
    Udp.read(packetBuffer, ETHERNET_BUF_MAX_SIZE);
    unsigned long highWord = word(packetBuffer[40], packetBuffer[41]);
    unsigned long lowWord = word(packetBuffer[42], packetBuffer[43]);
    unsigned long secsSince1900 = highWord << 16 | lowWord;
    Serial.print("Seconds since Jan 1 1900 = ");
    Serial.println(secsSince1900);
    Serial.print("Unix time = ");
    const unsigned long seventyYears = 2208988800UL;
    unsigned long epoch = secsSince1900 - seventyYears;
    Serial.println(epoch);
    Serial.print("The UTC time is ");       // UTC is the time at Greenwich Meridian (GMT)
    Serial.print((epoch % 86400L) / 3600);  // print the hour (86400 equals secs per day)
    Serial.print(':');
    if (((epoch % 3600) / 60) < 10) {
      Serial.print('0');
    }
    Serial.print((epoch % 3600) / 60);  // print the minute (3600 equals secs per minute)
    Serial.print(':');
    if ((epoch % 60) < 10) {
      Serial.print('0');
    }
    Serial.println(epoch % 60);  // print the second
    memset(packetBuffer, 0, ETHERNET_BUF_MAX_SIZE);
  }
}
老是只能收到5 6个包，就不动了，怎么办？