ethernet: support OpenCores ethernet MAC

OpenCores Ethernet MAC has a relatively simple interface, and is
already supported in QEMU. This makes it a good candidate for enabling
network support when running IDF apps in QEMU, compared to the
relatively more complex task of writing a QEMU model of ESP32 EMAC.

This driver is written with QEMU in mind: it does not implement or
handle things that aren't implemented or handled in the QEMU model:
error flags, error interrupts. The transmit part of the driver also
assumes that the TX operation is done immediately when the TX
descriptor is written (which is the case with QEMU), hence waiting for
the TX operation to complete is not necessary.

For simplicity, the driver assumes that the peripheral register
occupy the same memory range as the ESP32 EMAC registers, and the
same interrupt source number is used.


* Original commit: espressif/esp-idf@31dac92e5f

examples/common_components/protocol_examples_common/Kconfig.projbuild

@@ -49,6 +49,17 @@ menu "Example Connection Configuration"
                 select ETH_USE_SPI_ETHERNET
                 help
                     Select external SPI-Ethernet module.
+
+            config EXAMPLE_USE_OPENETH
+                bool "OpenCores Ethernet MAC (EXPERIMENTAL)"
+                select ETH_USE_OPENETH
+                help
+                    When this option is enabled, the example is built with support for
+                    OpenCores Ethernet MAC, which allows testing the example in QEMU.
+                    Note that this option is used for internal testing purposes, and
+                    not officially supported. Examples built with this option enabled
+                    will not run on a real ESP32 chip.
+
         endchoice
 
         if EXAMPLE_USE_INTERNAL_ETHERNET

examples/common_components/protocol_examples_common/connect.c

@@ -232,7 +232,12 @@ static void start(void)
     eth_dm9051_config_t dm9051_config = ETH_DM9051_DEFAULT_CONFIG(spi_handle);
     s_mac = esp_eth_mac_new_dm9051(&dm9051_config, &mac_config);
     s_phy = esp_eth_phy_new_dm9051(&phy_config);
+#elif CONFIG_EXAMPLE_USE_OPENETH
+    phy_config.autonego_timeout_ms = 100;
+    s_mac = esp_eth_mac_new_openeth(&mac_config);
+    s_phy = esp_eth_phy_new_dp83848(&phy_config);
 #endif
+
     esp_eth_config_t config = ETH_DEFAULT_CONFIG(s_mac, s_phy);
     ESP_ERROR_CHECK(esp_eth_driver_install(&config, &s_eth_handle));
     s_connection_name = "Ethernet";