Receive Ethernet Packets on DE-4 board with NIOS II

Hi, :)

I have a DE-4 board to which I would like to receive Ethernet packets from my PC. I have run the example provided with the tutorial (using triple-speed Ethernet on DE-4 boards) and it works as expected. I have got the exact same architecture as specified on that tutorial, with the NIOS II soft processor. But when I remove one end of the Ethernet cable and connect that end to my laptop's Ethernet port, ISR does not seem to be firing (Here I removed the cable on eth0 interface and kept the connection on eth1). I checked traffic on the Ethernet network using Wireshark and packets are sent out from the laptop (mostly broadcasts).

This is what I have got working now. (loopback on eth0)

#include <altera_avalon_sgdma.h>
# include <altera_avalon_sgdma_descriptor.h>
# include <altera_avalon_sgdma_regs.h>
# include "sys/alt_stdio.h"
# include "sys/alt_irq.h"
# include <unistd.h>
// Function Prototypes
void rx_ethernet_isr (void *context);
volatile char *onchip_control = (char *) 0x00000FFF;
volatile char *onchip_data_rx = (char *) 0x00001000;
volatile char *onchip_data_tx = (char *) 0x00008000;
// Global Variables
unsigned int text_length;
// Create a transmit frame
unsigned char tx_frame = {
	0x00,0x00, 						// for 32-bit alignment
	0xFF,0xFF,0xFF,0xFF,0xFF,0xFF, 	// destination address (broadcast)
	0x01,0x60,0x6E,0x11,0x02,0x0F, 	// source address
	0x03,0xF0, 						// length or type of the payload data
	'\0' 							// payload data (ended with termination character)
};
// Create a receive frame
unsigned char rx_frame = { 0 };
// Create sgdma transmit and receive devices
alt_sgdma_dev * sgdma_tx_dev;
alt_sgdma_dev * sgdma_rx_dev;
// Allocate descriptors in the descriptor_memory (onchip memory)
alt_sgdma_descriptor tx_descriptor		__attribute__ (( section ( ".descriptor_memory" )));
alt_sgdma_descriptor tx_descriptor_end	__attribute__ (( section ( ".descriptor_memory" )));
alt_sgdma_descriptor rx_descriptor  	__attribute__ (( section ( ".descriptor_memory" )));
alt_sgdma_descriptor rx_descriptor_end  __attribute__ (( section ( ".descriptor_memory" )));
/********************************************************************************
 * This program demonstrates use of the Ethernet in the DE4 board.
 *
 * It performs the following:
 *  1. Records input text and transmits the text via Ethernet after Enter is
 *     pressed
 *  2. Displays text received via Ethernet frame on the JTAG UART
********************************************************************************/
int main(void)
{
	// Open the sgdma transmit device
	sgdma_tx_dev = alt_avalon_sgdma_open ("/dev/sgdma_tx");
	if (sgdma_tx_dev == NULL) {
		alt_printf ("Error: could not open scatter-gather dma transmit device\n");
		return -1;
	} else alt_printf ("Opened scatter-gather dma transmit device\n");
	// Open the sgdma receive device
	sgdma_rx_dev = alt_avalon_sgdma_open ("/dev/sgdma_rx");
	if (sgdma_rx_dev == NULL) {
		alt_printf ("Error: could not open scatter-gather dma receive device\n");
		return -1;
	} else alt_printf ("Opened scatter-gather dma receive device\n");
	// Set interrupts for the sgdma receive device
	alt_avalon_sgdma_register_callback( sgdma_rx_dev, (alt_avalon_sgdma_callback) rx_ethernet_isr, 0x00000014, NULL );
	// Create sgdma receive descriptor
	alt_avalon_sgdma_construct_stream_to_mem_desc( &rx_descriptor, &rx_descriptor_end, (alt_u32 *)rx_frame, 0, 0 );
	// Set up non-blocking transfer of sgdma receive descriptor
	alt_avalon_sgdma_do_async_transfer( sgdma_rx_dev, &rx_descriptor );
	// Triple-speed Ethernet MegaCore base address
	volatile int * tse = (int *) 0x00083000; //tse.control_port at Qsys address map
	// Initialize the MAC address
	*(tse + 3) = 0x116E6001;
	*(tse + 4) = 0x00000F02;
	// Specify the addresses of the PHY devices to be accessed through MDIO interface
	*(tse + 0x0F) = 0x10;
	*(tse + 0x10) = 0x00;
	// Write to register 20 of the PHY chip for Ethernet port 0 to set up line loopback
	*(tse + 0xB4) = 0x4000;
	// Set the PCS to operate at SGMII mode	and enable SGMII auto-negotiation
	*(tse + 0x94) = *(tse + 0x94) | 0x0003;
	// Set PHY address for accessing the PHY chip for Ethernet port 1
	*(tse + 0x10) = 0x01;
	// Write to register 16 of the PHY to enable automatic crossover for all modes
	*(tse + 0xB0) = *(tse + 0xB0) | 0x0060;
	// Software reset the PHY chip and wait
	*(tse + 0xA0) = *(tse + 0xA0) | 0x8000;
	while ( *(tse + 0xA0) & 0x8000  )
		;
	// Enable read and write transfers, gigabit Ethernet operation, and CRC forwarding
	*(tse + 2) = *(tse + 2) | 0x0000004B;
	alt_printf( "send> " );
	text_length = 0;
	while (1) {
		char new_char;
		tx_frame = '\0';
		//Read the PCIe received data
		int i;
        while( *onchip_control != 'B' ) ;// polling the control byte
        i = 0;
        while( (new_char = *(onchip_data_tx + i) ) != '\n' ) {
            if (text_length < 1007) {
                // Add the new character to the output text
                if ( new_char >= 'a' && new_char <= 'z' )
                    tx_frame = new_char - 'a' + 'A';
                else if ( new_char >= 'A' && new_char <= 'Z' )
                    tx_frame = new_char - 'A' + 'a';
                else
                    tx_frame = '#';
                text_length++;
                // Maintain the terminal character after the text
                tx_frame = '\0';
            }
            i++;
        }
		 *onchip_control = 'K' ; // keep the control in the board until receive
		// Create transmit sgdma descriptor
		alt_avalon_sgdma_construct_mem_to_stream_desc( &tx_descriptor, &tx_descriptor_end, (alt_u32 *)tx_frame, 1024, 0, 1, 1, 0 );
		// Set up non-blocking transfer of sgdma transmit descriptor
		alt_avalon_sgdma_do_async_transfer( sgdma_tx_dev, &tx_descriptor );
		// Wait until transmit descriptor transfer is complete
		while (alt_avalon_sgdma_check_descriptor_status(&tx_descriptor) != 0)
			;
	}
	return 0;
}
/****************************************************************************************
 * Subroutine to read incoming Ethernet frames
****************************************************************************************/
void rx_ethernet_isr (void *context)
{
	int i;
	// Wait until receive descriptor transfer is complete
	while (alt_avalon_sgdma_check_descriptor_status(&rx_descriptor) != 0)
		;
	// Clear input line before writing
	for (i = 0; i < (6 + text_length); i++) {
		alt_printf( "%c", 0x08 );		 // 0x08 --> backspace
	}
	// Output received text
	alt_printf( "\nreceive> %s\n", rx_frame + 16 );
    while( *onchip_control != 'K' ) ;// polling the control byte
    for (i = 0; i < (6 + text_length); i++) {
    *(onchip_data_rx + i) = rx_frame;
    }
	*onchip_control = 'H' ; // pass the control right to the host PC
	// Reprint current input line after the output
	alt_printf( "\nsend> %s", tx_frame + 16 );
	// Create new receive sgdma descriptor
	alt_avalon_sgdma_construct_stream_to_mem_desc( &rx_descriptor, &rx_descriptor_end, (alt_u32 *)rx_frame, 0, 0 );
	// Set up non-blocking transfer of sgdma receive descriptor
	alt_avalon_sgdma_do_async_transfer( sgdma_rx_dev, &rx_descriptor );
	text_length = 0;
}

How do I change the above to receive Ethernet traffic on DE-4? :( Sorry if this is too simple and thanks a lot in advance!