Allow non-CYW43 network interfaces (W5500, etc.)

WIP - Builds and can get a DHCP address using W5500.

Lots of infrastructure work still required:
[ ] Separate CYW43 stuff and LWIP stuff (mutex, etc.)
[ ] Add async worker for pumping frames
[ ] Real LWIP-only mutex
[ ] Should WiFiClient be available as TCPClient?
etc.

Fixes #775

cores/rp2040/lwip_wrap.cpp

@@ -30,11 +30,11 @@
 class LWIPMutex {
 public:
     LWIPMutex() {
-        cyw43_arch_lwip_begin();
+        //        cyw43_arch_lwip_begin();
     }
 
     ~LWIPMutex() {
-        cyw43_arch_lwip_end();
+        //      cyw43_arch_lwip_end();
     }
 };
 

libraries/lwIP_Ethernet/src/LwipEthernet.cpp

@@ -1,13 +1,15 @@
 
 #include <LwipEthernet.h>
-//#include <SPI.h>
+#include <SPI.h>
+#include <lwip/init.h>
 
 //#ifndef ETHERNET_SPI_CLOCK_DIV
 //#define ETHERNET_SPI_CLOCK_DIV SPI_CLOCK_DIV4  // 4MHz (SPI.h)
 //#endif
 
 void SPI4EthInit() {
-    //SPI.begin();
+    SPI.begin();
+    lwip_init();
     //    SPI.setClockDivider(ETHERNET_SPI_CLOCK_DIV);
     //    SPI.setBitOrder(MSBFIRST);
     //    SPI.setDataMode(SPI_MODE0);

libraries/lwIP_Ethernet/src/LwipIntfDev.h

@@ -121,10 +121,10 @@ class LwipIntfDev: public LwipIntf, public RawDev {
     static err_t netif_init_s(netif* netif);
     static err_t linkoutput_s(netif* netif, struct pbuf* p);
     static void  netif_status_callback_s(netif* netif);
-
+public:
     // called on a regular basis or on interrupt
     err_t handlePackets();
-
+protected:
     // members
 
     netif _netif;

libraries/lwIP_w5500/examples/TelnetConnect/TelnetConnect.ino

@@ -0,0 +1,98 @@
+#include <LwipEthernet.h>
+#include <W5500lwIP.h>
+#include <WiFi.h>
+
+Wiznet5500lwIP eth(/*SS*/ 1);  // <== adapt to your hardware
+
+const char* host = "djxmmx.net";
+const uint16_t port = 17;
+
+void setup() {
+  SPI.setSCK(2);
+  SPI.setTX(3);
+  SPI.setRX(0);
+  SPI.setCS(1);
+
+  delay(5000);
+  Serial.begin(115200);
+
+  Serial.println("\nEthernet\n");
+
+  // 1. Currently when no default is set, esp8266-Arduino uses the first
+  //    DHCP client interface receiving a valid address and gateway to
+  //    become the new lwIP default interface.
+  // 2. Otherwise - when using static addresses - lwIP for every packets by
+  //    defaults selects automatically the best suited output interface
+  //    matching the destination address.  If several interfaces match,
+  //    the first one is picked.  On esp8266/Arduno: WiFi interfaces are
+  //    checked first.
+  // 3. Or, use `::setDefault()` to force routing through this interface.
+  // eth.setDefault(); // default route set through this interface
+
+  if (!ethInitDHCP(eth)) {
+    Serial.printf("no hardware found\n");
+    while (1) {
+      delay(1000);
+    }
+  }
+
+  while (!eth.connected()) {
+    eth.handlePackets();
+    sys_check_timeouts();
+    Serial.printf(".");
+    delay(1000);
+  }
+
+  Serial.printf("Ethernet: IP Address: %s\n",
+                eth.localIP().toString().c_str());
+}
+
+void loop() {
+
+  Serial.print("connecting to ");
+  Serial.print(host);
+  Serial.print(':');
+  Serial.println(port);
+
+  Serial.printf("Link sense: %d (detectable: %d)\n", eth.isLinked(), eth.isLinkDetectable());
+
+  // Use WiFiClient class to create TCP connections
+  // (this class could have been named TCPClient)
+  WiFiClient client;
+  if (!client.connect(host, port)) {
+    Serial.println("connection failed");
+    delay(5000);
+    return;
+  }
+
+  // This will send a string to the server
+  Serial.println("sending data to server");
+  if (client.connected()) {
+    client.println("hello from ESP8266");
+  }
+
+  // wait for data to be available
+  unsigned long timeout = millis();
+  while (client.available() == 0) {
+    if (millis() - timeout > 5000) {
+      Serial.println(">>> Client Timeout !");
+      client.stop();
+      delay(60000);
+      return;
+    }
+  }
+
+  // Read all the lines of the reply from server and print them to Serial
+  Serial.println("receiving from remote server");
+  while (client.available()) {
+    char ch = static_cast<char>(client.read());
+    Serial.print(ch);
+  }
+
+  // Close the connection
+  Serial.println();
+  Serial.println("closing connection");
+  client.stop();
+
+  delay(300000);  // execute once every 5 minutes, don't flood remote service
+}

libraries/lwIP_w5500/library.properties

@@ -0,0 +1,10 @@
+name=lwIP_w5500
+version=1
+author=Nicholas Humfrey
+maintainer=esp8266/Arduino
+sentence=Ethernet driver
+paragraph=Wiznet5500 ethernet drivers for lwIP and esp8266 Arduino from https://github.com/njh/W5500MacRaw
+category=Communication
+url=https://github.com/esp8266/Arduino
+architectures=rp2040
+dot_a_linkage=true

libraries/lwIP_w5500/src/W5500lwIP.h

@@ -0,0 +1,10 @@
+
+#ifndef _W5500LWIP_H
+#define _W5500LWIP_H
+
+#include <LwipIntfDev.h>
+#include <utility/w5500.h>
+
+using Wiznet5500lwIP = LwipIntfDev<Wiznet5500>;
+
+#endif  // _W5500LWIP_H