Accessing hardware registers in Linux userspace

Question

I wpuld like to write to hardware registers on OMAP3530 in Linux userspace. Please, find below code. Mmap returns error:

Memory map failed. error -1

mmap: Pe

Answer 1

The documentation for mmap() says (emphasis mine):

The mmap() function shall fail if:

EACCES

The fildes argument is not open for read, regardless of the protection specified, or fildes is not open for write and PROT_WRITE was specified for a MAP_SHARED type mapping.

Since you specify PROT_WRITE, the file should be open for write. Your code only opens it for read.