NAME

       rtapi_shmem - Functions for managing shared memory blocks

SYNTAX

               int rtapi_shmem_new(int key, int module_id, unsigned long int size)

               int rtapi_shmem_delete(int shmem_id, int module_id)

               int rtapi_shmem_getptr(int shmem_id, void ** ptr)

ARGUMENTS

       key    Identifies  the memory block.  Key must be nonzero.  All modules wishing to use the
              same memory must use the same key.

       module_id
              Module identifier returned by a prior call to rtapi_init.

       size   The desired size of the shared memory block, in bytes

       ptr    The pointer to the shared memory block.  Note that the block may  be  mapped  at  a
              different address for different modules.

DESCRIPTION

       rtapi_shmem_new  allocates a block of shared memory.  key identifies the memory block, and
       must be non-zero.  All modules wishing to access the same memory must use  the  same  key.
       module_id  is  the  ID  of the module that is making the call (see rtapi_init).  The block
       will be at least size bytes, and may be rounded up.  Allocating many small blocks  may  be
       very  wasteful.  When a particular block is allocated for the first time, the contents are
       zeroed.  Subsequent allocations of the same block by other modules or processes  will  not
       touch  the contents of the block.  Applications can use those bytes to see if they need to
       initialize the block, or if another module already did  so.   On  success,  it  returns  a
       positive  integer  ID,  which is used for all subsequent calls dealing with the block.  On
       failure it returns a negative error code.

       rtapi_shmem_delete frees the shared memory block associated with shmem_id.   module_id  is
       the ID of the calling module.  Returns a status code.

       rtapi_shmem_getptr sets *ptr to point to shared memory block associated with shmem_id.

REALTIME CONSIDERATIONS

       rtapi_shmem_getptr may be called from user code, init/cleanup code, or realtime tasks.

       rtapi_shmem_new and rtapi_shmem_dete may not be called from realtime tasks.

RETURN VALUE