EthernetLWIP (Wired Ethernet) Support

Wired Ethernet interfaces are supported for all the internal networking libraries (WiFiClient, WiFiClientSecure, WiFiServer, WiFiServerSecure, WiFiUDP, WebServer, Updater, HTTPClient, etc.).

Using these wired interfaces is very similar to using the Pico-W WiFi so most examples in the core only require minor modifications to use a wired interface.

Supported Wired Ethernet Modules

  • Wiznet W5100(s)

  • Wiznet W5500

  • ENC28J60

Enabling Wired Ethernet

Simply replace the WiFi include at the top with:

#include <W5500lwIP.h> // Or W5100lwIP.h or ENC28J60.h

And add a global Ethernet object of the same type:

Wiznet5500lwIP eth(1); // Parameter is the Chip Select pin

In your setup() you may adjust the SPI pins you’re using to match your hardware (be sure they are legal for the RP2040!), or skip this if you’re using the default ones:

void setup() {
    SPI.setRX(0);
    SPI.setCS(1);
    SPI.setSCK(2);
    SPI.setTX(3);
    ....
}

And finally replace the WiFi.begin() and WiFi.connected() calls with eth.begin() and eth.connected():

void setup() {
    ....
    // WiFi.begin(SSID, PASS)
    eth.begin();

    //while (!WiFi.connected()) {
    while (!eth.connected()) {
        Serial.print(".");
    }

    Serial.print("IP address: ");
    //Serial.println(WiFi.localIP());
    Serial.println(eth.localIP());

    ....
}

Adjusting LWIP Polling

LWIP operates in a polling mode for the wired Ethernet devices. By default it will run every 20ms, meaning that on average it will take half that time (10ms) before a packet received in the Ethernet module is received and operated upon by the Pico. This gives very low CPU utilization but in some cases this latency can affect performance.

Adding a call to lwipPollingPeriod(XXX) (where XXXX is the polling period in milliseconds) can adjust this setting on the fly. Note that if you set it too low, the Pico may not have enough time to service the Ethernet port before the timer fires again, leading to a lock up and hang.

Using Interrupt-Driven Handling

The WizNet and ENC28J60 devices support generating an interrupt when a packet is received, removing the need for polling and decreasing latency. Simply specify the SPI object to use and the interrupt pin when instantiating the Ethernet object:

#include <W5100lwIP.h>
Wiznet5100lwIP eth(SS /* Chip Select*/, SPI /* SPI interface */, 17 /* Interrupt GPIO */ );

Adjusting SPI Speed

By default a 4MHz clock will be used to clock data into and out of the Ethernet module. Depending on the module and your wiring, a higher SPI clock may increase performance (but too high of a clock will cause communications problems or hangs).

This value may be adjusted using the eth.setSPISpeed(hz) call before starting the device. (You may also use custom SPISettings instead via eth.setSPISettings(spis)`)

For example, to set the W5500 to use a 30MHZ clock:

#include <W5500lwIP.h>
Wiznet5500lwIP eth(1);

void setup() {
    eth.setSPISpeed(30000000);
    lwipPollingPeriod(3);
    ...
    eth.begin();
    ...
}

Using the WIZnet W5100S-EVB-Pico

You can use the onboard Ethernet chip with these drivers, in interrupt mode, by utilizing the following options:

#include <W5100lwIP.h>
Wiznet5100lwIP eth(17, SPI, 21);  // Note chip select is **17**

void setup() {
    // Set SPI to the onboard Wiznet chip
    SPI.setRX(16);
    SPI.setCS(17);
    SPI.setSCK(18);
    SPI.setTX(19);
    ...
    eth.begin();
    ...
}

Example Code

The following examples allow switching between WiFi and Ethernet:

  • WebServer/AdvancedWebServer

  • HTTPClient/BasicHTTPSClient

Caveats

The same restrictions for WiFi apply to these Ethernet classes, namely:

  • Only core 0 may run any networking related code.

  • In FreeRTOS, only the setup and loop task can call networking libraries, not any tasks.

Special Thanks

  • LWIPEthernet classes come from the ESP8266 Arduino team

  • Individual Ethernet drivers were written by Nicholas Humfrey