bus error when memcopy to uio mmap device

Question

I currently try to access UIO shared memory via memcopy.

My approach is:

1. open the corresponding device
2. map the memory via mmap with the offset speciality N*getpagesize()
3. memcopy / memset to the pointer that is returned from mmap

I tried also with ftruncate after Step 2 resulting in an error.

The memcopy / memset causes a bus error which is normaly a sign of writing out of the files boundaries.

Via cat /proc/'pid'/maps I'm able to see that there is a mapping for /dev/uioX Also /sys/class/uio/uioX/maps/ has two map directories, of which I try to access the second one (map1 therefore N = 1)

Am I missing out something? Would I have to mmap the full size of the memory specified in /sys/class/uio/uioX/maps/map1/size ?

I could not find any example for accessing the memory via memcopy, is there something that prevents memcopy on UIO mmaped memory?

Sources

unsigned char* GetMemPtr(const char *name, unsigned long Size)
{
    long fd;
    long truncret;
    void* MemPtr;

    unsigned long offst;

    printf("Opening: %s with size %u\n" , name, Size);

    fd = open(name, O_RDWR);

    if (fd < 0) {
        printf("Error: open : %u : %s\n", fd, strerror(errno));
    }

    offst = 1 * getpagesize();

    /*truncret = ftruncate(fd, offst + Size);
    if (truncret < 0)
    {
        printf("Error: ftruncate : %s : %d\n", strerror(errno), truncret);

    }*/

    MemPtr = mmap(0, Size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, offst);
    if (MemPtr == MAP_FAILED)
    {
        printf("Error: mmap : %p : %s\n", MemPtr, strerror(errno));

    }
    //MemPtr = MemPtr + offst;

    printf("Mem pointer is %p\n", MemPtr);

    memset(MemPtr, 0, Size);

    printf("Pointer is : %p\n" , MemPtr);
    return (unsigned char*) MemPtr;

}

Results in the output:
Opening: /dev/uio0 with size 4096
Mem pointer is 0xffff89232000
Bus error (core dumped)