Unit PoE-P4 Ethernet Network Communication

#include <ETH.h>

#ifndef ETH_PHY_MDC
#define ETH_PHY_TYPE ETH_PHY_TLK110
#define ETH_PHY_ADDR  1
#define ETH_PHY_MDC   31
#define ETH_PHY_MDIO  52
#define ETH_PHY_POWER 51
#define ETH_CLK_MODE  EMAC_CLK_EXT_IN
#endif

static bool eth_connected = false;

// WARNING: onEvent is called from a separate FreeRTOS task (thread)!
void onEvent(arduino_event_id_t event) {
  switch (event) {
    case ARDUINO_EVENT_ETH_START:
      Serial.println("ETH Started");
      // The hostname must be set after the interface is started, but needs
      // to be set before DHCP, so set it from the event handler thread.
      ETH.setHostname("esp32-ethernet");
      break;
    case ARDUINO_EVENT_ETH_CONNECTED: Serial.println("ETH Connected"); break;
    case ARDUINO_EVENT_ETH_GOT_IP:
      Serial.println("ETH Got IP");
      Serial.println(ETH);
      eth_connected = true;
      break;
    case ARDUINO_EVENT_ETH_LOST_IP:
      Serial.println("ETH Lost IP");
      eth_connected = false;
      break;
    case ARDUINO_EVENT_ETH_DISCONNECTED:
      Serial.println("ETH Disconnected");
      eth_connected = false;
      break;
    case ARDUINO_EVENT_ETH_STOP:
      Serial.println("ETH Stopped");
      eth_connected = false;
      break;
    default: break;
  }
}

void testClient(const char *host, uint16_t port) {
  Serial.print("\nconnecting to ");
  Serial.println(host);

  NetworkClient client;
  if (!client.connect(host, port)) {
    Serial.println("connection failed");
    return;
  }
  client.printf("GET / HTTP/1.1\r\nHost: %s\r\n\r\n", host);
  while (client.connected() && !client.available());
  while (client.available()) {
    Serial.write(client.read());
  }

  Serial.println("closing connection\n");
  client.stop();
}

void setup() {
  Serial.begin(115200);
  Network.onEvent(onEvent);  // Will call onEvent() from another thread.
  ETH.begin(ETH_PHY_TYPE, ETH_PHY_ADDR, ETH_PHY_MDC, ETH_PHY_MDIO, ETH_PHY_POWER, ETH_CLK_MODE);
}

void loop() {
  if (eth_connected) {
    testClient("baidu.com", 80);
  }
  delay(10000);
}