Doxygen does not generate function documentation

I'm trying to use doxygen for the first time.

I'm using it in order document some C library, and structures.

I think to use the correct tags, but the documentation is good only as far the define macros are concerned, but the function tags (\fn) are completely ignored. I attach below an example of one my tagged comment:

`/*!    \file   cab.h`

    \author dan
    \date   20/12/2013
    \brief  cab

`*/
   /*! \def NOT_SPECIFIED`

     \brief Constant value that indicates the not specification of a parameter
  ` */`

   `#define NOT_SPECIFIED 0`

    /*! \fn         cab_create
     \brief     allocates the memory space and resources for the CAB
     \param     c cab to create
     \param     dim_buf size of the data contained in each buffer
     \param     maximum number of buffer
     \param     protocol used to handle priority inversion 
     \param     ceiling value of the ceiling,
     \return    1 if it completes successfully, -1 otherwise
    */`
    int cab_create(cab *c, int dim_buf, int max_buf, int protocol, int ceiling);