diff --git a/part14-ethernet/Makefile b/part14-ethernet/Makefile
index 1e3608f..ea9f2be 100644
--- a/part14-ethernet/Makefile
+++ b/part14-ethernet/Makefile
@@ -2,7 +2,7 @@ CFILES = $(wildcard *.c lib/*.c kernel/*.c net/*.c)
 SFILES = $(wildcard boot/*.S lib/*.S kernel/*.S)
 OFILES = $(CFILES:.c=.o) $(SFILES:.S=.o)
 LLVMPATH = /opt/homebrew/opt/llvm/bin
-CLANGFLAGS = -Wall -O2 -ffreestanding -nostdlib -mcpu=cortex-a72+nosimd
+CLANGFLAGS = -Wall -O0 -ffreestanding -nostdlib -mcpu=cortex-a72+nosimd
 
 all: clean kernel8.img
 
diff --git a/part14-ethernet/Makefile.gcc b/part14-ethernet/Makefile.gcc
index 674751a..d8316fd 100644
--- a/part14-ethernet/Makefile.gcc
+++ b/part14-ethernet/Makefile.gcc
@@ -1,7 +1,7 @@
 CFILES = $(wildcard *.c lib/*.c kernel/*.c net/*.c)
 SFILES = $(wildcard boot/*.S lib/*.S kernel/*.S)
 OFILES = $(CFILES:.c=.o) $(SFILES:.S=.o)
-GCCFLAGS = -Wall -O2 -ffreestanding -nostdlib -nostartfiles
+GCCFLAGS = -Wall -O0 -ffreestanding -nostdlib -nostartfiles
 GCCPATH = ../../gcc-arm-10.3-2021.07-x86_64-aarch64-none-elf/bin
 
 all: clean kernel8.img
diff --git a/part14-ethernet/include/spi.h b/part14-ethernet/include/spi.h
index c5fca8b..6454a72 100644
--- a/part14-ethernet/include/spi.h
+++ b/part14-ethernet/include/spi.h
@@ -1,5 +1,5 @@
 void spi_init();
-void spi_send_recv(unsigned char *sbuffer, unsigned char *rbuffer, unsigned int size);
+unsigned int spi_send_recv(unsigned char *sbuffer, unsigned char *rbuffer, unsigned int size);
 void spi_send(unsigned char *data, unsigned int size);
 void spi_recv(unsigned char *data, unsigned int size);
 void spi_send_no_selection(unsigned char command);
diff --git a/part14-ethernet/kernel/arp.c b/part14-ethernet/kernel/arp.c
new file mode 100644
index 0000000..8cb2a94
--- /dev/null
+++ b/part14-ethernet/kernel/arp.c
@@ -0,0 +1,201 @@
+#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();
+}
diff --git a/part14-ethernet/kernel/irq.c b/part14-ethernet/kernel/irq.c
index 3ab82d1..bc2276a 100644
--- a/part14-ethernet/kernel/irq.c
+++ b/part14-ethernet/kernel/irq.c
@@ -1,4 +1,27 @@
 #include "kernel.h"
+#include "../include/fb.h"
+
+char *entry_error_messages[] = {
+   "SYNC_INVALID_EL1t",
+   "IRQ_INVALID_EL1t",		
+   "FIQ_INVALID_EL1t",		
+   "ERROR_INVALID_EL1T",		
+
+   "SYNC_INVALID_EL1h",		
+   "IRQ_INVALID_EL1h",		
+   "FIQ_INVALID_EL1h",		
+   "ERROR_INVALID_EL1h",		
+
+   "SYNC_INVALID_EL0_64",		
+   "IRQ_INVALID_EL0_64",		
+   "FIQ_INVALID_EL0_64",		
+   "ERROR_INVALID_EL0_64",	
+
+   "SYNC_INVALID_EL0_32",		
+   "IRQ_INVALID_EL0_32",		
+   "FIQ_INVALID_EL0_32",		
+   "ERROR_INVALID_EL0_32"	
+};
 
 void enable_interrupt_controller() {
     REGS_IRQ->irq0_enable_0 = SYS_TIMER_IRQ_1 | SYS_TIMER_IRQ_3;
@@ -8,6 +31,14 @@ void disable_interrupt_controller() {
     REGS_IRQ->irq0_enable_0 = 0;
 }
 
+void show_invalid_entry_message(int type, unsigned long esr, unsigned long address) {
+    debugstr(entry_error_messages[type]);
+    debugstr(" ESR: ");
+    debughex(esr);
+    debugstr("Addr: ");
+    debughex(address);
+}
+
 void handle_irq() {
     unsigned int irq = REGS_IRQ->irq0_pending_0;
 
diff --git a/part14-ethernet/kernel/irqentry.S b/part14-ethernet/kernel/irqentry.S
index d24ae00..28d0b94 100644
--- a/part14-ethernet/kernel/irqentry.S
+++ b/part14-ethernet/kernel/irqentry.S
@@ -67,11 +67,7 @@
 	mov	x0, #\type
 	mrs	x1, esr_el1
 	mrs	x2, elr_el1
-
-        // We could pass this to a function to print an error here
-        // e.g. bl show_invalid_entry_message
-        //
-        // For now we'll just hang
+        bl      show_invalid_entry_message
 
 	b	err_hang
 .endm
diff --git a/part14-ethernet/kernel/kernel.c b/part14-ethernet/kernel/kernel.c
index 139c7a0..e0b4a0d 100644
--- a/part14-ethernet/kernel/kernel.c
+++ b/part14-ethernet/kernel/kernel.c
@@ -8,10 +8,10 @@
 void initProgress(void)
 {
     drawRect(0, 0, 301, 50, 0x0f, 0);
-    drawString(309, 21, "Core 0", 0x0f, 1);
+    drawString(309, 21, "Core 1", 0x0f, 1);
 
     drawRect(0, 60, 301, 110, 0x0f, 0);
-    drawString(309, 81, "Core 1", 0x0f, 1);
+    drawString(309, 81, "Core 2", 0x0f, 1);
 
     drawRect(0, 120, 301, 170, 0x0f, 0);
     drawString(309, 141, "Timer 1", 0x0f, 1);
@@ -28,21 +28,24 @@ void drawProgress(unsigned int core, unsigned int val) {
     if (val > 0) drawRect(1, (60 * core) + 1, (val * 3), (60 * core) + 49, col, 1);
 }
 
-void core0_main(void)
-{
-    unsigned int core0_val = 0;
+unsigned int c2_done = 0;
 
-    while (core0_val <= 100) {
+void core2_main(void)
+{
+    unsigned int core2_val = 0;
+
+    clear_core2();                // Only run once
+
+    while (core2_val <= 100) {
        wait_msec(0x100000);
-       drawProgress(0, core0_val);
-       core0_val++;
+       drawProgress(1, core2_val);
+       core2_val++;
     }
 
-    debugstr("Core 0 done.");
+    debugstr("Core 2 done.");
     debugcrlf();
 
-    irq_disable();
-    disable_interrupt_controller();
+    c2_done = 1;
 
     while(1);
 }
@@ -55,7 +58,7 @@ void core1_main(void)
 
     while (core1_val <= 100) {
        wait_msec(0x3FFFF);
-       drawProgress(1, core1_val);
+       drawProgress(0, core1_val);
        core1_val++;
     }
 
@@ -132,37 +135,6 @@ unsigned int HAL_GetTick(void) {
     return timer_get_ticks();
 }
 
-void init_network(void)
-{
-    ENC_HandleTypeDef handle;
-
-    unsigned char macaddr[6];
-    macaddr[0] = 0xc0;
-    macaddr[1] = 0xff;
-    macaddr[2] = 0xee;
-    macaddr[3] = 0xc0;
-    macaddr[4] = 0xff;
-    macaddr[5] = 0xee;
-
-    debugstr("Setting MAC address to C0:FF:EE:C0:FF:EE.");
-    debugcrlf();
-
-    handle.Init.DuplexMode = ETH_MODE_FULLDUPLEX;
-    handle.Init.MACAddr = macaddr;
-    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();
-}
-
 void main(void)
 {
     fb_init();
@@ -172,20 +144,35 @@ void main(void)
 
     initProgress();
 
+    // Kick it off on core 1&2
+
+    start_core1(core1_main);
+    start_core2(core2_main);
+
     // Kick off the timers
 
     irq_init_vectors();
     enable_interrupt_controller();
     irq_enable();
     timer_init();
+
+    // Test the network card
+
     spi_init();
     init_network();
+    arp_test();
 
-    // Kick it off on core 1
+    // The work is done - wait for timers to get done
 
-    start_core1(core1_main);
+    debugstr("Core 0 done.");
+    debugcrlf();
 
-    // Loop endlessly
+    while (!c2_done);
 
-    core0_main();
+    // Disable IRQs and loop endlessly
+
+    irq_disable();
+    disable_interrupt_controller();
+
+    while(1);
 }
diff --git a/part14-ethernet/kernel/kernel.h b/part14-ethernet/kernel/kernel.h
index 5ff14d5..acaa894 100644
--- a/part14-ethernet/kernel/kernel.h
+++ b/part14-ethernet/kernel/kernel.h
@@ -49,3 +49,6 @@ unsigned long timer_get_ticks();
 void timer_sleep(unsigned int ms);
 void HAL_Delay(volatile unsigned int Delay);
 unsigned int HAL_GetTick(void);
+
+void init_network(void);
+void arp_test(void);
diff --git a/part14-ethernet/lib/spi.c b/part14-ethernet/lib/spi.c
index c6b0bd5..d71fc22 100644
--- a/part14-ethernet/lib/spi.c
+++ b/part14-ethernet/lib/spi.c
@@ -52,7 +52,7 @@ void spi_chip_select(unsigned char chip_select) {
     REGS_SPI0->cs = (REGS_SPI0->cs & ~CS_CS) | (chip_select << CS_CS__SHIFT);
 }
 
-void spi_send_recv(unsigned char *sbuffer, unsigned char *rbuffer, unsigned int size) {
+unsigned int spi_send_recv(unsigned char *sbuffer, unsigned char *rbuffer, unsigned int size) {
     REGS_SPI0->data_length = size;
     REGS_SPI0->cs = REGS_SPI0->cs | CS_CLEAR_RX | CS_CLEAR_TX | CS_TA;
     
@@ -89,6 +89,7 @@ void spi_send_recv(unsigned char *sbuffer, unsigned char *rbuffer, unsigned int
     }
 
     REGS_SPI0->cs = (REGS_SPI0->cs & ~CS_TA);
+    return read_count;
 }
 
 void spi_send(unsigned char *data, unsigned int size) {
diff --git a/part14-ethernet/net/enc28j60.c b/part14-ethernet/net/enc28j60.c
index 52ba6a5..57189d3 100644
--- a/part14-ethernet/net/enc28j60.c
+++ b/part14-ethernet/net/enc28j60.c
@@ -993,7 +993,7 @@ void ENC_WriteBuffer(void *buffer, uint16_t buflen)
 }
 
 /****************************************************************************
- * Function: enc_rdbuffer
+ * Function: ENC_ReadBuffer
  *
  * Description:
  *   Read a buffer of data.
@@ -1003,15 +1003,17 @@ void ENC_WriteBuffer(void *buffer, uint16_t buflen)
  *   buflen  - The number of bytes to read
  *
  * Returned Value:
- *   None
+ *   read_count - Number of bytes received
  *
  * Assumptions:
  *   Read pointer is set to the correct address
  *
  ****************************************************************************/
 
-static void enc_rdbuffer(void *buffer, int16_t buflen)
+uint8_t ENC_ReadBuffer(void *buffer, uint16_t buflen)
 {
+  uint8_t read_count = 0;
+
   /* Select ENC28J60 chip */
 
   ENC_SPI_Select(true);
@@ -1022,9 +1024,11 @@ static void enc_rdbuffer(void *buffer, int16_t buflen)
 
   /* Then read the buffer data */
 
-  ENC_SPI_SendBuf(NULL, buffer, buflen);
+  read_count = ENC_SPI_SendBuf(NULL, buffer, buflen);
 
   /* De-select ENC28J60 chip: done in ENC_SPI_SendBuf callback */
+
+  return read_count;
 }
 
 /****************************************************************************
@@ -1187,7 +1191,7 @@ void ENC_Transmit(ENC_HandleTypeDef *handle)
                 enc_wrbreg(handle, ENC_ERDPTL, addtTsv4 & 0xff);
                 enc_wrbreg(handle, ENC_ERDPTH, addtTsv4 >> 8);
 
-                enc_rdbuffer(&tsv4, 1);
+                ENC_ReadBuffer(&tsv4, 1);
                 regval = enc_rdgreg(ENC_EIR);
                 if (!(regval & EIR_TXERIF) || !(tsv4 & TSV_LATECOL)) {
                     break;
@@ -1242,7 +1246,7 @@ bool ENC_GetReceivedFrame(ENC_HandleTypeDef *handle)
     * and wrap to the beginning of the read buffer as necessary)
     */
 
-    enc_rdbuffer(rsv, 6);
+    ENC_ReadBuffer(rsv, 6);
 
     /* Decode the new next packet pointer, and the RSV.  The
     * RSV is encoded as:
@@ -1281,7 +1285,7 @@ bool ENC_GetReceivedFrame(ENC_HandleTypeDef *handle)
             * end_rdbuffer (above).
             */
 
-            enc_rdbuffer(handle->RxFrameInfos.buffer, handle->RxFrameInfos.length);
+            ENC_ReadBuffer(handle->RxFrameInfos.buffer, handle->RxFrameInfos.length);
 
         }
     }
diff --git a/part14-ethernet/net/enc28j60.h b/part14-ethernet/net/enc28j60.h
index 7c378c0..c34152a 100644
--- a/part14-ethernet/net/enc28j60.h
+++ b/part14-ethernet/net/enc28j60.h
@@ -98,10 +98,10 @@ void ENC_SPI_Send(uint8_t command);
   * Implement SPI buffer send and receive. Must be provided by user code
   * param  master2slave: data to be sent from host to ENC28J60, can be NULL if we only want to receive data from slave
   * param  slave2master: answer from ENC28J60 to host, can be NULL if we only want to send data to slave
-  * retval none
+  * retval read_count: number of bytes read (if applicable)
   */
 
-void ENC_SPI_SendBuf(uint8_t *master2slave, uint8_t *slave2master, uint16_t bufferSize);
+unsigned int ENC_SPI_SendBuf(uint8_t *master2slave, uint8_t *slave2master, uint16_t bufferSize);
 
 /* Exported types ------------------------------------------------------------*/
 /** @defgroup ETH_Exported_Types ETH Exported Types
@@ -686,6 +686,7 @@ int8_t ENC_RestoreTXBuffer(ENC_HandleTypeDef *handle, uint16_t len);
  ****************************************************************************/
 
 void ENC_WriteBuffer(void *buffer, uint16_t buflen);
+uint8_t ENC_ReadBuffer(void *buffer, uint16_t buflen);
 
 /****************************************************************************
  * Function: ENC_Transmit
diff --git a/part14-ethernet/net/encspi.c b/part14-ethernet/net/encspi.c
index 524f73f..91c41b1 100644
--- a/part14-ethernet/net/encspi.c
+++ b/part14-ethernet/net/encspi.c
@@ -4,10 +4,14 @@ void ENC_SPI_Select(unsigned char truefalse) {
     spi_chip_select(!truefalse); // If it's true, select 0 (the ENC), if false, select 1 (i.e. deselect the ENC)
 }
 
-void ENC_SPI_SendBuf(unsigned char *master2slave, unsigned char *slave2master, unsigned short bufferSize) {
+unsigned int ENC_SPI_SendBuf(unsigned char *master2slave, unsigned char *slave2master, unsigned short bufferSize) {
+    unsigned int read_count = 0;
+
     spi_chip_select(0);
-    spi_send_recv(master2slave, slave2master, bufferSize);
+    read_count = spi_send_recv(master2slave, slave2master, bufferSize);
     spi_chip_select(1); // De-select the ENC
+ 
+    return read_count;
 }
 
 void ENC_SPI_Send(unsigned char command) {