Configure the ep_filter to accept ARP broadcasts to LM32

Hook a new socket to tap ARP messages
Process ARP messages into replies

lib/arp.c

+static wr_socket_t arp_socket;
+static uint8_t myMAC[6];
+static uint8_t myIP[4];
+
+#define ARP_HTYPE	0
+#define ARP_PTYPE	(ARP_HTYPE+2)
+#define ARP_HLEN	(ARP_PTYPE+2)
+#define ARP_PLEN	(ARP_HLEN+1)
+#define ARP_OPER	(ARP_PLEN+1)
+#define ARP_SHA		(ARP_OPER+2)
+#define ARP_SPA		(ARP_SHA+6)
+#define ARP_THA		(ARP_SPA+4)
+#define ARP_TPA		(ARP_THA+6)
+#define ARP_END		(ARP_TPA+4)
+
+unsigned int ipv4_checksum(unsigned short* buf, int shorts) {
+  int i;
+  unsigned int sum;
+  
+  sum = 0;
+  for (i = 0; i < shorts; ++i)
+    sum += buf[i];
+  
+  sum = (sum >> 16) + (sum & 0xffff);
+  sum += (sum >> 16);
+  
+  return (~sum & 0xffff);
+}
+
+void arp_init(const char* if_name, uint32_t ip) {
+  wr_sockaddr_t saddr;
+  uint32_t ip_bigendian;
+  
+  /* Configure socket filter */
+  memset(&saddr, 0, sizeof(saddr));
+  strcpy(saddr.if_name, if_name);
+  memset(&saddr.mac, 0xFF, 6); /* Broadcast */
+  saddr.ethertype = htons(0x0806); /* ARP */
+  saddr.family = PTPD_SOCK_RAW_ETHERNET;
+  
+  /* Configure ARP parameters */
+  ip_bigendian = htonl(ip);
+  memcpy(myIP, &ip_bigendian, 4);
+  get_mac_addr(myMAC);
+  
+  arp_socket = ptpd_netif_create_socket(PTPD_SOCK_RAW_ETHERNET, 0, &saddr);
+}
+
+static int process_arp(char* buffer) {
+  uint8_t hisMAC[6];
+  uint8_t hisIP[4];
+  
+  /* Is it ARP request targetting our IP? */
+  if (buffer[ARP_OPER+0] != 0 ||
+      buffer[ARP_OPER+1] != 1 ||
+      memcmp(buffer+ARP_TPA, myIP, 4))
+    return 0;
+
+  memcpy(hisMAC, buffer+ARP_SHA, 6);
+  memcpy(hisIP,  buffer+ARP_SPA, 4);
+
+  // ------------- ARP ------------  
+  // HW ethernet
+  buf[ARP_HTYPE+0] = 0;
+  buf[ARP_HTYPE+1] = 1;
+  // proto IP
+  buf[ARP_PTYPE+0] = 8;
+  buf[ARP_PTYPE+1] = 0;
+  // lengths
+  buf[ARP_HLEN] = 6;
+  buf[ARP_PLEN] = 4;
+  // Response
+  buf[ARP_OPER+0] = 0;
+  buf[ARP_OPER+1] = 2;
+  // my MAC+IP
+  memcpy(buf+ARP_SHA, myMAC, 6);
+  memcpy(buf+ARP_SPA, myIP,  4);
+  // his MAC+IP
+  memcpy(buf+ARP_THA, hisMAC, 6);
+  memcpy(buf+ARP_TPA, hisIP,  4);
+  
+  return 1;
+}
+
+void arp_poll() {
+  char buffer[ARP_END];
+  wr_sockaddr_t addr;
+  int len;
+  
+  if ((len = ptpd_netif_recvfrom(&arp_socket, &addr, buffer, sizeof(buffer), 0)) > 0)
+    if (process_arp(buffer) > 0)
+      ptp_netif_sendto(&arp_socket, &addr, buffer, sizeof(buffer), 0);
+}