From fd6dc8c8de4dbc7ecf8a82a597cd5b43476fc8e3 Mon Sep 17 00:00:00 2001 From: Amar Takhar Date: Sun, 17 Jan 2016 19:19:43 -0500 Subject: Split document into seperate files by section. --- c_user/dual_ports_memory_manager.rst | 296 +++++++++++++++++++++++++++++++++++ 1 file changed, 296 insertions(+) create mode 100644 c_user/dual_ports_memory_manager.rst (limited to 'c_user/dual_ports_memory_manager.rst') diff --git a/c_user/dual_ports_memory_manager.rst b/c_user/dual_ports_memory_manager.rst new file mode 100644 index 0000000..471cefc --- /dev/null +++ b/c_user/dual_ports_memory_manager.rst @@ -0,0 +1,296 @@ +Dual-Ported Memory Manager +########################## + +.. index:: ports +.. index:: dual ported memory + +Introduction +============ + +The dual-ported memory manager provides a mechanism +for converting addresses between internal and external +representations for multiple dual-ported memory areas (DPMA). +The directives provided by the dual-ported memory manager are: + +- ``rtems_port_create`` - Create a port + +- ``rtems_port_ident`` - Get ID of a port + +- ``rtems_port_delete`` - Delete a port + +- ``rtems_port_external_to_internal`` - Convert external to internal address + +- ``rtems_port_internal_to_external`` - Convert internal to external address + +Background +========== +.. index:: dual ported memory, definition +.. index:: external addresses, definition +.. index:: internal addresses, definition + +A dual-ported memory area (DPMA) is an contiguous +block of RAM owned by a particular processor but which can be +accessed by other processors in the system. The owner accesses +the memory using internal addresses, while other processors must +use external addresses. RTEMS defines a port as a particular +mapping of internal and external addresses. + +There are two system configurations in which +dual-ported memory is commonly found. The first is +tightly-coupled multiprocessor computer systems where the +dual-ported memory is shared between all nodes and is used for +inter-node communication. The second configuration is computer +systems with intelligent peripheral controllers. These +controllers typically utilize the DPMA for high-performance data +transfers. + +Operations +========== + +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. + +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. + +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. + +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. + +Directives +========== + +This section details the dual-ported memory manager’s +directives. A subsection is dedicated to each of this manager’s +directives and describes the calling sequence, related +constants, usage, and status codes. + +PORT_CREATE - Create a port +--------------------------- +.. index:: create a port + +**CALLING SEQUENCE:** + +.. index:: rtems_port_create + +.. code:: c + + rtems_status_code rtems_port_create( + rtems_name name, + void \*internal_start, + void \*external_start, + uint32_t length, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - port created successfully +``RTEMS_INVALID_NAME`` - invalid port name +``RTEMS_INVALID_ADDRESS`` - address not on four byte boundary +``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL +``RTEMS_TOO_MANY`` - too many DP memory areas created + +**DESCRIPTION:** + +This directive creates a port which resides on the +local node for the specified DPMA. The assigned port id is +returned in id. This port id is used as an argument to other +dual-ported memory manager directives to convert addresses +within this DPMA. + +For control and maintenance of the port, RTEMS +allocates and initializes an DPCB from the DPCB free pool. Thus +memory from the dual-ported memory area is not used to store the +DPCB. + +**NOTES:** + +The internal_address and external_address parameters +must be on a four byte boundary. + +This directive will not cause the calling task to be +preempted. + +PORT_IDENT - Get ID of a port +----------------------------- +.. index:: get ID of a port +.. index:: obtain ID of a port + +**CALLING SEQUENCE:** + +.. index:: rtems_port_ident + +.. code:: c + + rtems_status_code rtems_port_ident( + rtems_name name, + rtems_id \*id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - port identified successfully +``RTEMS_INVALID_ADDRESS`` - ``id`` is NULL +``RTEMS_INVALID_NAME`` - port name not found + +**DESCRIPTION:** + +This directive obtains the port id associated with +the specified name to be acquired. If the port name is not +unique, then the port id will match one of the DPMAs with that +name. However, this port id is not guaranteed to correspond to +the desired DPMA. The port id is used to access this DPMA in +other dual-ported memory area related directives. + +**NOTES:** + +This directive will not cause the running task to be +preempted. + +PORT_DELETE - Delete a port +--------------------------- +.. index:: delete a port + +**CALLING SEQUENCE:** + +.. index:: rtems_port_delete + +.. code:: c + + rtems_status_code rtems_port_delete( + rtems_id id + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_SUCCESSFUL`` - port deleted successfully +``RTEMS_INVALID_ID`` - invalid port id + +**DESCRIPTION:** + +This directive deletes the dual-ported memory area +specified by id. The DPCB for the deleted dual-ported memory +area is reclaimed by RTEMS. + +**NOTES:** + +This directive will not cause the calling task to be +preempted. + +The calling task does not have to be the task that +created the port. Any local task that knows the port id can +delete the port. + +PORT_EXTERNAL_TO_INTERNAL - Convert external to internal address +---------------------------------------------------------------- +.. index:: convert external to internal address + +**CALLING SEQUENCE:** + +.. index:: rtems_port_external_to_internal + +.. code:: c + + rtems_status_code rtems_port_external_to_internal( + rtems_id id, + void \*external, + void \**internal + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_INVALID_ADDRESS`` - ``internal`` is NULL +``RTEMS_SUCCESSFUL`` - successful conversion + +**DESCRIPTION:** + +This directive converts a dual-ported memory address +from external to internal representation for the specified port. +If the given external address is invalid for the specified +port, then the internal address is set to the given external +address. + +**NOTES:** + +This directive is callable from an ISR. + +This directive will not cause the calling task to be +preempted. + +PORT_INTERNAL_TO_EXTERNAL - Convert internal to external address +---------------------------------------------------------------- +.. index:: convert internal to external address + +**CALLING SEQUENCE:** + +.. index:: rtems_port_internal_to_external + +.. code:: c + + rtems_status_code rtems_port_internal_to_external( + rtems_id id, + void \*internal, + void \**external + ); + +**DIRECTIVE STATUS CODES:** + +``RTEMS_INVALID_ADDRESS`` - ``external`` is NULL +``RTEMS_SUCCESSFUL`` - successful conversion + +**DESCRIPTION:** + +This directive converts a dual-ported memory address +from internal to external representation so that it can be +passed to owner of the DPMA represented by the specified port. +If the given internal address is an invalid dual-ported address, +then the external address is set to the given internal address. + +**NOTES:** + +This directive is callable from an ISR. + +This directive will not cause the calling task to be +preempted. + +.. COMMENT: COPYRIGHT (c) 1988-2008. + +.. COMMENT: On-Line Applications Research Corporation (OAR). + +.. COMMENT: All rights reserved. + -- cgit v1.2.3