rpi4-osdev/part14-ethernet/kernel/arp.c

#include "../net/enc28j60.h"
#include "../include/fb.h"

// Structure for Ethernet header

typedef struct {
   uint8_t DestAddrs[6];
   uint8_t SrcAddrs[6];
   uint16_t type;
} EtherNetII;

// Ethernet packet types

#define ARPPACKET 0x0806
#define IPPACKET  0x0800

// Structure for an ARP Packet

typedef struct {
   EtherNetII eth;
   uint16_t hardware;
   uint16_t protocol;
   uint8_t hardwareSize;
   uint8_t protocolSize;
   uint16_t opCode;
   uint8_t senderMAC[6];
   uint8_t senderIP[4];
   uint8_t targetMAC[6];
   uint8_t targetIP[4];
} ARP;

// ARP OpCodes

#define ARPREPLY   0x0002
#define ARPREQUEST 0x0001

// ARP hardware types

#define ETHERNET 0x0001

// MAC address to be assigned to the ENC28J60

uint8_t myMAC[6] = { 0xc0, 0xff, 0xee, 0xc0, 0xff, 0xee };

// Router MAC is not known to start with, and requires an ARP reply to find out

uint8_t routerMAC[6] = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff };

// IP address to be assigned to the ENC28J60

uint8_t deviceIP[4] = { 192, 168, 0, 66 };

// IP Address of the router, whose hardware address we will find using the ARP request

uint8_t routerIP[4] = { 192, 168, 0, 1 };

// HELPER FUNCTIONS

void *memset(void *dest, uint8_t val, uint16_t len)
{
    uint8_t *ptr = dest;
    while (len-- > 0)
       *ptr++ = val;
    return dest;
}

void *memcpy(void *dest, const void *src, uint16_t len)
{
    uint8_t *d = dest;
    const uint8_t *s = src;
    while (len--)
       *d++ = *s++;
    return dest;
}

uint8_t memcmp(void *str1, void *str2, unsigned count)
{
    uint8_t *s1 = str1;
    uint8_t *s2 = str2;

    while (count-- > 0)
    {
       if (*s1++ != *s2++)
          return s1[-1] < s2[-1] ? -1 : 1;
    }

    return 0;
}

// MAIN FUNCTIONS

void SendArpPacket(uint8_t *targetIP, uint8_t *deviceMAC)
{
   /* Parameters:
    *   targetIP - The target IP Address for the ARP request (the one whose hardware
    *              address we want)
    *   deviceMAC - The MAC address of the ENC28J60, i.e. the source MAC for the ARP
    *               request
   */

   ARP arpPacket;

   // The source of the packet will be the ENC28J60 MAC address
   memcpy(arpPacket.eth.SrcAddrs, deviceMAC, 6);
    
   // The destination is broadcast - a MAC address of FF:FF:FF:FF:FF:FF */
   memset(arpPacket.eth.DestAddrs, 0xFF, 6);
    
   arpPacket.eth.type = ARPPACKET;
   arpPacket.hardware = ETHERNET;
    
   // We want an IP address resolved

   arpPacket.protocol = IPPACKET;
   arpPacket.hardwareSize = 0x06; // sizeof(deviceMAC);
   arpPacket.protocolSize = 0x04; // sizeof(deviceIP);
   arpPacket.opCode = ARPREQUEST;
  
   // Target MAC is set to 0 as it is unknown
   memset(arpPacket.targetMAC, 0, 6);
    
   // Sender MAC is the ENC28J60's MAC address
   memcpy(arpPacket.senderMAC, deviceMAC, 6);
    
   // The target IP is the IP address we want resolved
   memcpy(arpPacket.targetIP, targetIP, 4);
  
   // Check if the last reply has come from an IP address that we want i.e. someone else is already using it
   if (!memcmp(targetIP, deviceIP, 4)) {
      // Yes, someone is using our IP so set the sender IP to 0.0.0.0
      memset(arpPacket.senderIP, 0, 4);
   } else {
      // No, nobody is using our IP so we can use it confidently
      memcpy(arpPacket.senderIP, deviceIP, 4);
   }

   // Send the packet
   ENC_WriteBuffer((unsigned char*)&arpPacket, sizeof(ARP));
}

void arp_test(void)
{
   unsigned int tries = 0;
   ARP checkPacket;

   debugstr("Sending ARP request... ");

   SendArpPacket(routerIP, myMAC);

   debugstr("done.");
   debugcrlf();

   debugstr("Waiting for ARP response... ");
   debugcrlf();

   while (tries < 1000) {
      if (ENC_ReadBuffer((unsigned char *)&checkPacket, sizeof(ARP)) == 0) {
         continue;
      }
      if (!memcmp(checkPacket.senderIP, routerIP, 4)) {
         // Success! We have found our router's MAC address

         memcpy(routerMAC, checkPacket.senderMAC, 6);
         debugstr("Router MAC is ");
         debughex(routerMAC[0]);
         debughex(routerMAC[1]);
         debughex(routerMAC[2]);
         debughex(routerMAC[3]);
         debughex(routerMAC[4]);
         debughex(routerMAC[5]);
         debugcrlf();
      }
      tries++;
   }

   debugstr("Timed out.");
   debugcrlf();
}

void init_network(void)
{
   ENC_HandleTypeDef handle;

   debugstr("Setting MAC address to C0:FF:EE:C0:FF:EE.");
   debugcrlf();

   handle.Init.DuplexMode = ETH_MODE_FULLDUPLEX;
   handle.Init.MACAddr = myMAC;
   handle.Init.ChecksumMode = ETH_CHECKSUM_BY_HARDWARE;
   handle.Init.InterruptEnableBits = 0;

   debugstr("Starting network up.");
   debugcrlf();

   if (!ENC_Start(&handle)) {
      debugstr("Could not initialise network card.");
   } else {
      debugstr("Network card successfully initialised.");
   }
   debugcrlf();
}