Split net stack into eth/arp/ipv4/icmp, deferred handler responses, ping tests

firmware/include/eth.h

@@ -0,0 +1,20 @@
+#pragma once
+#include <array>
+#include <cstdint>
+
+namespace eth {
+
+using mac_addr = std::array<uint8_t, 6>;
+
+static constexpr mac_addr MAC_BROADCAST = {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};
+static constexpr uint16_t ETH_ARP = __builtin_bswap16(0x0806);
+static constexpr uint16_t ETH_IPV4 = __builtin_bswap16(0x0800);
+
+struct __attribute__((packed)) header {
+    mac_addr dst;
+    mac_addr src;
+    uint16_t ethertype;
+};
+static_assert(sizeof(header) == 14);
+
+} // namespace eth