Bus Error: Dev/mem Timer4 Beagle Bone Black

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I am working on Beagle Bone Black TIMER4. I wanted to access the registers directly from user space and so opted for dev/mem. But I end up getting bus error when I try to read the contents in a memory address. The code is posted below:

#include <unistd.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <stdio.h>
#include<stdlib.h>
#include<string.h>
#include <signal.h>

#define TIMER4_START_addr 0x48044000
#define TIDR 0x00
#define TIOCP_CFG 0x10

int main()
{
   unsigned int reg;

   char *timer_addr = NULL;

   printf("\n Start Pgm");

    int mem, integer;

    if ((mem = open ("/dev/mem", O_RDWR | O_SYNC)) < 0)
    {
        printf("Cannot open /dev/mem\n");

        return 1;
    }

    printf("Opened /dev/mem\n");

    timer_addr = mmap(0, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, mem, TIMER4_START_addr);

    printf("GPIO mapped to %p\n", timer_addr);

    reg =  *((int*) timer_addr);

    printf("GPIO1 configuration: %x\n", reg);

    return 0;
}

The output that I get is :

Start
PgmOpened /dev/mem
GPIO mapped to 0xb6fb7000
Bus error

Please let me know how to overcome this problem.

Regards Anand