How to read from a onchip memory

Device driver to acess on chip memory as a char device (must be made inside linux2.6/arch/nios2/driver)

# include <linux/fs.h># include <linux/sched.h># include <linux/errno.h># include <linux/types.h># include <linux/cdev.h># include <linux/kernel.h># include <linux/module.h># include <asm/current.h># include <asm/segment.h># include <asm/uaccess.h># include <asm/io.h>
# define DRIVER_NAME "shmem"
# define SHARED_MEM_BASE 0x800# define SHARED_MEM_SPAN 2048
typedef struct {
  int32_t mutex;
  int32_t reset;
} mutex_t;
typedef struct {
  mutex_t *mutex;
  unsigned char *buffer;
} shmem_t;
static shmem_t shmem;
int shmem_open(struct inode *inode,struct file *filep)
{
  return 0;
}
int shmem_release(struct inode *inode, struct file *filep)
{
  return 0;
}
ssize_t shmem_read(struct file *filep ,char *buff, size_t count, loff_t *offp)
{
  int retval;
  
  printk(KERN_INFO "read, count %i, off %i\n", count, *offp);
  
  if (*offp >= SHARED_MEM_SPAN) {
    return 0;
  }
  
  if (count > (SHARED_MEM_SPAN - *offp)) {
    count = (SHARED_MEM_SPAN - *offp);
  }
  
  
  retval = copy_to_user(buff, (shmem.buffer+*offp), count);
  if (retval != 0) {
    printk(KERN_ERR "Kernel to userspace copy failed!\n" );
    return retval;
  }
  *offp += count;
  
  return count;
}
ssize_t shmem_write(struct file *filep,const char *buff,size_t count,loff_t *offp )
{
  int retval;
  if (*offp >= SHARED_MEM_SPAN) {
    return -ENOSPC;
  }
  
  if (count > (SHARED_MEM_SPAN - *offp)) {
    count = (SHARED_MEM_SPAN - *offp);
  }
  retval = copy_from_user((shmem.buffer+*offp), buff, count);
  if (retval != 0) {
    printk(KERN_ERR "Kernel to userspace copy failed!\n" );
    return retval;
  }
  *offp += count;
  
  return count;
}
    
struct file_operations shmem_fops={
open: shmem_open,
read: shmem_read,
write: shmem_write,
release:shmem_release,
};
static int shmem_init(void) {
  printk(KERN_INFO "shmem device driver init\n");
  if(register_chrdev(222,DRIVER_NAME, &shmem_fops)){
    printk(KERN_ERR "failed to register\n");
    goto chrdev_error;
  }
  shmem.mutex = (mutex_t *)ioremap(MUTEX_BASE, MUTEX_SPAN);
  if (shmem.mutex == NULL) {
    printk(KERN_ERR "failed to map mutex\n");
    goto mutex_error;
  }
  
  printk(KERN_INFO "mutex %p\n", shmem.mutex);
  shmem.buffer = (unsigned char *)ioremap(SHARED_MEM_BASE, SHARED_MEM_SPAN);
  if (shmem.buffer == NULL) {
    printk(KERN_ERR "failed to map shared memory\n");
    goto buffer_error;
  }
  printk(KERN_INFO "shmem %p\n", shmem.buffer);
  
  printk(KERN_INFO "shmem: mutex.reset %02x\n", shmem.mutex->reset);
  return 0;
buffer_error:
  iounmap(shmem.mutex);
mutex_error:
  unregister_chrdev(222, DRIVER_NAME);
chrdev_error:
  return -ENODEV;
}
static void shmem_cleanup(void)
{
  printk(KERN_INFO "shmem device driver unregister.\n");
  iounmap(shmem.buffer);
  iounmap(shmem.mutex);
  unregister_chrdev(222, DRIVER_NAME);
  return;
}
module_init(shmem_init);
module_exit(shmem_cleanup);

# include <unistd.h># include <fcntl.h># include <sys/mman.h>
int main()
{
    int fd = 0;
    int value = 0;
    int bytes = 0;
    fd = open("/dev/mutex", O_RDWR);
    if (fd == NULL)
    {
        printf("Erro abrindo mutex\n");
        return 1;
    }
    bytes = read(fd, &value, sizeof(value));
    if (bytes < 0)
    {
        printf("Error lendo\n");
        return 1;
    }
    
    printf("Valor lido: %x\n", value);
    
    bytes = read(fd, &value, sizeof(value));
    if (bytes < 0)
    {
        printf("Error lendo\n");
        return 1;
    }
    
    printf("Valor lido: %x\n", value);
    
    lseek(fd, 0, SEEK_SET);
    
    bytes = read(fd, &value, sizeof(value));
    if (bytes < 0)
    {
        printf("Error lendo\n");
        return 1;
    }
    
    printf("Valor lido: %x\n", value);
    
    close(fd);
    return 0;
    
    
    
}