Layer: Foundation · Build flags: PC_ENABLE_ETHERNET, PC_ETH_W5500, PC_ETH_W5500_*

What this example teaches

The RMII path (Ethernet) needs a chip with an on-chip Ethernet MAC. The ESP32-S3 has no RMII MAC, so a wired link there uses an SPI Ethernet controller - the WIZnet W5500 - over the HSPI bus. With PC_ETH_W5500=1, init_eth_physical() calls the arduino-esp32 3.x ETH SPI API (ETH.begin(ETH_PHY_W5500, ...)); once the link has a DHCP IP the server accepts on it with no other change:

init_eth_physical();          // ETH.begin(ETH_PHY_W5500, ...) with the PC_ETH_W5500_* pins
while (!eth_ready()) delay(250);
// ... server.begin(80) - now serving over W5500 Ethernet

Nothing else changes: the egress reporting already classifies the wired route as pc_iface::PC_IFACE_ETH, so pc_net_egress(), per-route STA/AP/ETH interface filters, and every protocol work over the link the moment it has an IP.

Wiring (ESP32-S3-DevKitC, HSPI)

The pins come from the PC_ETH_W5500_* build flags in build_opt.h:

Signal	GPIO	Flag
`CS`	`7`	`PC_ETH_W5500_CS`
`RST`	`6`	`PC_ETH_W5500_RST`
`INT`	`5`	`PC_ETH_W5500_INT`
`SCLK`	`12`	`PC_ETH_W5500_SCK`
`MOSI`	`11`	`PC_ETH_W5500_MOSI`
`MISO`	`13`	`PC_ETH_W5500_MISO`

Plus VCC 3V3 and GND. Set the flags for your own wiring; see the hardware hookup guide for the full pinout.

SPI clock and throughput

PC_ETH_W5500_SPI_MHZ sets the SPI clock (default 20). Throughput is SPI-bound, not PHY-bound: measured on an ESP32-S3 it is ~7.2 Mbit/s at 20 MHz and ~8.2 Mbit/s at 24 MHz, plateauing near the W5500's internal ~8.3 Mbit/s ceiling around 30 MHz. Higher clocks need clean, short wiring - on breadboard jumpers, sustained transfers stay reliable to ~24 MHz and the SPI reads corrupt above ~33 MHz. Keep the default unless the W5500 is on a short, clean PCB trace. A 200 MB download completes byte-exact at the 20 MHz default. For near-100-Mbit speed use an RMII PHY (LAN8720, Ethernet) - the W5500 trades speed for needing no built-in MAC. See FEATURE_PERFORMANCE.md for the full clock-vs-throughput sweep.

Core requirement

W5500 SPI Ethernet is arduino-esp32 3.x only - the 2.x ETH library has no W5500 support (ETH_PHY_W5500 is undefined there). Build this with the arduino-cli / IDF-5.x core.

Build-flag note

The flags must reach the library build, so pass them as build flags:

pio ci --board=esp32-s3-devkitc-1 --project-option="framework=arduino" \
  --project-option="build_flags=-DPC_ENABLE_ETHERNET=1 -DPC_ETH_W5500=1 -DPC_ETH_W5500_CS=7 -DPC_ETH_W5500_RST=6 -DPC_ETH_W5500_INT=5 -DPC_ETH_W5500_SCK=12 -DPC_ETH_W5500_MISO=13 -DPC_ETH_W5500_MOSI=11" \
  --lib="." examples/Peripherals/EthernetW5500/EthernetW5500.ino

(The Arduino IDE reads the flags from build_opt.h beside the sketch automatically.)