19.3. Operations

19.3.1. Creating a Port

The rtems_port_create directive creates a port into a DPMA with the user-defined name. The user specifies the association between internal and external representations for the port being created. RTEMS allocates a Dual-Ported Memory Control Block (DPCB) from the DPCB free list to maintain the newly created DPMA. RTEMS also generates a unique dual-ported memory port ID which is returned to the calling task. RTEMS does not initialize the dual-ported memory area or access any memory within it.

19.3.2. Obtaining Port IDs

When a port is created, RTEMS generates a unique port ID and assigns it to the created port until it is deleted. The port ID may be obtained by either of two methods. First, as the result of an invocation of the``rtems_port_create`` directive, the task ID is stored in a user provided location. Second, the port ID may be obtained later using the rtems_port_ident directive. The port ID is used by other dual-ported memory manager directives to access this port.

19.3.3. Converting an Address

The rtems_port_external_to_internal directive is used to convert an address from external to internal representation for the specified port. The rtems_port_internal_to_external directive is used to convert an address from internal to external representation for the specified port. If an attempt is made to convert an address which lies outside the specified DPMA, then the address to be converted will be returned.

19.3.4. Deleting a DPMA Port

A port can be removed from the system and returned to RTEMS with the rtems_port_delete directive. When a port is deleted, its control block is returned to the DPCB free list.