Arduino mega + Ethernet shield + FastSPI library

#include <SPI.h>
#include <Ethernet.h>
#include <EthernetUdp.h>
#include <FastSPI_LED.h>

#define NUM_LEDS 160
struct CRGB { unsigned char r; unsigned char g; unsigned char b; };
struct CRGB *leds;
#define PIN 51

int i = 0;
long r;
long g;
long b;

// Enter a MAC address and IP address for your controller below.
// The IP address will be dependent on your local network:
byte mac[] = { 0x90, 0xA2, 0xDA, 0x0D, 0x4E, 0xEB };
IPAddress ip(192, 168, 100, 40);
unsigned int localPort = 41181;      // local port to listen on

// buffers for receiving and sending data
char packetBuffer[250]; //buffer to hold incoming packet,
char ReplyBuffer[] = "k";       // a string to send back to keep it synchronized

// An EthernetUDP instance to let us send and receive packets over UDP
EthernetUDP Udp;

void setup() {
  Serial.begin(115200);

  // Leds:
  FastSPI_LED.setLeds(NUM_LEDS);
  FastSPI_LED.setChipset(CFastSPI_LED::SPI_WS2801);
  FastSPI_LED.setPin(PIN);
  FastSPI_LED.setDataRate(5);
  FastSPI_LED.init();
  FastSPI_LED.start();
  leds = (struct CRGB*)FastSPI_LED.getRGBData();

  // start the Ethernet and UDP:
  Ethernet.begin(mac,ip);
  Udp.begin(localPort);

  while (Udp.parsePacket()) {
    Udp.flush();
  }
}

void loop() {
  long packetSize = Udp.parsePacket();

  if(Udp.available() && packetSize > 0)
  {
      Serial.println("got package!");
      Udp.read(packetBuffer,250);

      memset(leds, 0, NUM_LEDS * 3);

      for(i = 0 ; i < NUM_LEDS; i++ ) {
          leds[i].r = 0;
          leds[i].g = 0;
          leds[i].b = 255;
      }
      noInterrupts();
      FastSPI_LED.show();
      delay(10);
      interrupts();

      Udp.beginPacket(Udp.remoteIP(), Udp.remotePort());
      Udp.write(ReplyBuffer);
      Udp.endPacket();
  }
  else
  {
    Serial.println("no no no!");
    memset(leds, 0, NUM_LEDS * 3);
    for (i = 0; i < NUM_LEDS; i++) {
      leds[i].r = 0;
      leds[i].g = 0;
      leds[i].b = 0;
    }

    noInterrupts();
    FastSPI_LED.show();
    delay(10);
    interrupts();
  }
  delay(100);
}