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diff --git a/ada_user/message_manager.rst b/ada_user/message_manager.rst deleted file mode 100644 index 03903ec..0000000 --- a/ada_user/message_manager.rst +++ /dev/null @@ -1,697 +0,0 @@ -Message Manager -############### - -.. index:: messages -.. index:: message queues - -Introduction -============ - -The message manager provides communication and -synchronization capabilities using RTEMS message queues. The -directives provided by the message manager are: - -- ``rtems.message_queue_create`` - Create a queue - -- ``rtems.message_queue_ident`` - Get ID of a queue - -- ``rtems.message_queue_delete`` - Delete a queue - -- ``rtems.message_queue_send`` - Put message at rear of a queue - -- ``rtems.message_queue_urgent`` - Put message at front of a queue - -- ``rtems.message_queue_broadcast`` - Broadcast N messages to a queue - -- ``rtems.message_queue_receive`` - Receive message from a queue - -- ``rtems.message_queue_get_number_pending`` - Get number of messages pending on a queue - -- ``rtems.message_queue_flush`` - Flush all messages on a queue - -Background -========== - -Messages --------- - -A message is a variable length buffer where -information can be stored to support communication. The length -of the message and the information stored in that message are -user-defined and can be actual data, pointer(s), or empty. - -Message Queues --------------- - -A message queue permits the passing of messages among -tasks and ISRs. Message queues can contain a variable number of -messages. Normally messages are sent to and received from the -queue in FIFO order using the ``rtems.message_queue_send`` -directive. However, the ``rtems.message_queue_urgent`` -directive can be used to place -messages at the head of a queue in LIFO order. - -Synchronization can be accomplished when a task can -wait for a message to arrive at a queue. Also, a task may poll -a queue for the arrival of a message. - -The maximum length message which can be sent is set -on a per message queue basis. The message content must be copied in general -to/from an internal buffer of the message queue or directly to a peer in -certain cases. This copy operation is performed with interrupts disabled. So -it is advisable to keep the messages as short as possible. - -Building a Message Queue Attribute Set --------------------------------------- -.. index:: message queue attributes - -In general, an attribute set is built by a bitwise OR -of the desired attribute components. The set of valid message -queue attributes is provided in the following table: - -- ``RTEMS.FIFO`` - tasks wait by FIFO (default) - -- ``RTEMS.PRIORITY`` - tasks wait by priority - -- ``RTEMS.LOCAL`` - local message queue (default) - -- ``RTEMS.GLOBAL`` - global message queue - -An attribute listed as a default is not required to -appear in the attribute list, although it is a good programming -practice to specify default attributes. If all defaults are -desired, the attribute ``RTEMS.DEFAULT_ATTRIBUTES`` -should be specified on this call. - -This example demonstrates the attribute_set parameter -needed to create a local message queue with the task priority -waiting queue discipline. The attribute_set parameter to the``rtems.message_queue_create`` directive could be either``RTEMS.PRIORITY`` or``RTEMS.LOCAL or RTEMS.PRIORITY``. -The attribute_set parameter can be set to ``RTEMS.PRIORITY`` -because ``RTEMS.LOCAL`` is the default for all created -message queues. If a similar message queue were to be known globally, then the -attribute_set parameter would be``RTEMS.GLOBAL or RTEMS.PRIORITY``. - -Building a MESSAGE_QUEUE_RECEIVE Option Set -------------------------------------------- - -In general, an option is built by a bitwise OR of the -desired option components. The set of valid options for the``rtems.message_queue_receive`` directive are -listed in the following table: - -- ``RTEMS.WAIT`` - task will wait for a message (default) - -- ``RTEMS.NO_WAIT`` - task should not wait - -An option listed as a default is not required to -appear in the option OR list, although it is a good programming -practice to specify default options. If all defaults are -desired, the option ``RTEMS.DEFAULT_OPTIONS`` should -be specified on this call. - -This example demonstrates the option parameter needed -to poll for a message to arrive. The option parameter passed to -the ``rtems.message_queue_receive`` directive should -be ``RTEMS.NO_WAIT``. - -Operations -========== - -Creating a Message Queue ------------------------- - -The ``rtems.message_queue_create`` directive creates a message -queue with the user-defined name. The user specifies the -maximum message size and maximum number of messages which can be -placed in the message queue at one time. The user may select -FIFO or task priority as the method for placing waiting tasks in -the task wait queue. RTEMS allocates a Queue Control Block -(QCB) from the QCB free list to maintain the newly created queue -as well as memory for the message buffer pool associated with -this message queue. RTEMS also generates a message queue ID -which is returned to the calling task. - -For GLOBAL message queues, the maximum message size -is effectively limited to the longest message which the MPCI is -capable of transmitting. - -Obtaining Message Queue IDs ---------------------------- - -When a message queue is created, RTEMS generates a -unique message queue ID. The message queue ID may be obtained -by either of two methods. First, as the result of an invocation -of the ``rtems.message_queue_create`` directive, the -queue ID is stored in a user provided location. Second, the queue -ID may be obtained later using the ``rtems.message_queue_ident`` -directive. The queue ID is used by other message manager -directives to access this message queue. - -Receiving a Message -------------------- - -The ``rtems.message_queue_receive`` directive attempts to -retrieve a message from the specified message queue. If at -least one message is in the queue, then the message is removed -from the queue, copied to the caller’s message buffer, and -returned immediately along with the length of the message. When -messages are unavailable, one of the following situations -applies: - -- By default, the calling task will wait forever for the - message to arrive. - -- Specifying the ``RTEMS.NO_WAIT`` option forces an immediate return - with an error status code. - -- Specifying a timeout limits the period the task will - wait before returning with an error status. - -If the task waits for a message, then it is placed in -the message queue’s task wait queue in either FIFO or task -priority order. All tasks waiting on a message queue are -returned an error code when the message queue is deleted. - -Sending a Message ------------------ - -Messages can be sent to a queue with the``rtems.message_queue_send`` and``rtems.message_queue_urgent`` directives. These -directives work identically when tasks are waiting to receive a -message. A task is removed from the task waiting queue, -unblocked, and the message is copied to a waiting task’s -message buffer. - -When no tasks are waiting at the queue,``rtems.message_queue_send`` places the -message at the rear of the message queue, while``rtems.message_queue_urgent`` places the message at the -front of the queue. The message is copied to a message buffer -from this message queue’s buffer pool and then placed in the -message queue. Neither directive can successfully send a -message to a message queue which has a full queue of pending -messages. - -Broadcasting a Message ----------------------- - -The ``rtems.message_queue_broadcast`` directive sends the same -message to every task waiting on the specified message queue as -an atomic operation. The message is copied to each waiting -task’s message buffer and each task is unblocked. The number of -tasks which were unblocked is returned to the caller. - -Deleting a Message Queue ------------------------- - -The ``rtems.message_queue_delete`` directive removes a message -queue from the system and frees its control block as well as the -memory associated with this message queue’s message buffer pool. -A message queue can be deleted by any local task that knows the -message queue’s ID. As a result of this directive, all tasks -blocked waiting to receive a message from the message queue will -be readied and returned a status code which indicates that the -message queue was deleted. Any subsequent references to the -message queue’s name and ID are invalid. Any messages waiting -at the message queue are also deleted and deallocated. - -Directives -========== - -This section details the message 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. - -MESSAGE_QUEUE_CREATE - Create a queue -------------------------------------- -.. index:: create a message queue - -**CALLING SEQUENCE:** - -.. code:: c - - procedure Message_Queue_Create ( - Name : in RTEMS.Name; - Count : in RTEMS.Unsigned32; - Max_Message_Size : in RTEMS.Unsigned32; - Attribute_Set : in RTEMS.Attribute; - ID : out RTEMS.ID; - Result : out RTEMS.Status_Codes - ); - -**DIRECTIVE STATUS CODES:** - -``RTEMS.SUCCESSFUL`` - queue created successfully -``RTEMS.INVALID_NAME`` - invalid queue name -``RTEMS.INVALID_ADDRESS`` - ``id`` is NULL -``RTEMS.INVALID_NUMBER`` - invalid message count -``RTEMS.INVALID_SIZE`` - invalid message size -``RTEMS.TOO_MANY`` - too many queues created -``RTEMS.UNSATISFIED`` - unable to allocate message buffers -``RTEMS.MP_NOT_CONFIGURED`` - multiprocessing not configured -``RTEMS.TOO_MANY`` - too many global objects - -**DESCRIPTION:** - -This directive creates a message queue which resides -on the local node with the user-defined name specified in name. -For control and maintenance of the queue, RTEMS allocates and -initializes a QCB. Memory is allocated from the RTEMS Workspace -for the specified count of messages, each of max_message_size -bytes in length. The RTEMS-assigned queue id, returned in id, -is used to access the message queue. - -Specifying ``RTEMS.PRIORITY`` in attribute_set causes tasks -waiting for a message to be serviced according to task priority. -When ``RTEMS.FIFO`` is specified, waiting tasks are serviced -in First In-First Out order. - -**NOTES:** - -This directive will not cause the calling task to be -preempted. - -The following message queue attribute constants are -defined by RTEMS: - -- ``RTEMS.FIFO`` - tasks wait by FIFO (default) - -- ``RTEMS.PRIORITY`` - tasks wait by priority - -- ``RTEMS.LOCAL`` - local message queue (default) - -- ``RTEMS.GLOBAL`` - global message queue - -Message queues should not be made global unless -remote tasks must interact with the created message queue. This -is to avoid the system overhead incurred by the creation of a -global message queue. When a global message queue is created, -the message queue’s name and id must be transmitted to every -node in the system for insertion in the local copy of the global -object table. - -For GLOBAL message queues, the maximum message size -is effectively limited to the longest message which the MPCI is -capable of transmitting. - -The total number of global objects, including message -queues, is limited by the maximum_global_objects field in the -configuration table. - -MESSAGE_QUEUE_IDENT - Get ID of a queue ---------------------------------------- -.. index:: get ID of a message queue - -**CALLING SEQUENCE:** - -.. code:: c - - procedure Message_Queue_Ident ( - Name : in RTEMS.Name; - Node : in RTEMS.Unsigned32; - ID : out RTEMS.ID; - Result : out RTEMS.Status_Codes - ); - -**DIRECTIVE STATUS CODES:** - -``RTEMS.SUCCESSFUL`` - queue identified successfully -``RTEMS.INVALID_ADDRESS`` - ``id`` is NULL -``RTEMS.INVALID_NAME`` - queue name not found -``RTEMS.INVALID_NODE`` - invalid node id - -**DESCRIPTION:** - -This directive obtains the queue id associated with -the queue name specified in name. If the queue name is not -unique, then the queue id will match one of the queues with that -name. However, this queue id is not guaranteed to correspond to -the desired queue. The queue id is used with other message -related directives to access the message queue. - -**NOTES:** - -This directive will not cause the running task to be -preempted. - -If node is ``RTEMS.SEARCH_ALL_NODES``, all nodes are searched -with the local node being searched first. All other nodes are -searched with the lowest numbered node searched first. - -If node is a valid node number which does not -represent the local node, then only the message queues exported -by the designated node are searched. - -This directive does not generate activity on remote -nodes. It accesses only the local copy of the global object -table. - -MESSAGE_QUEUE_DELETE - Delete a queue -------------------------------------- -.. index:: delete a message queue - -**CALLING SEQUENCE:** - -.. code:: c - - procedure Message_Queue_Delete ( - ID : in RTEMS.ID; - Result : out RTEMS.Status_Codes - ); - -**DIRECTIVE STATUS CODES:** - -``RTEMS.SUCCESSFUL`` - queue deleted successfully -``RTEMS.INVALID_ID`` - invalid queue id -``RTEMS.ILLEGAL_ON_REMOTE_OBJECT`` - cannot delete remote queue - -**DESCRIPTION:** - -This directive deletes the message queue specified by -id. As a result of this directive, all tasks blocked waiting to -receive a message from this queue will be readied and returned a -status code which indicates that the message queue was deleted. -If no tasks are waiting, but the queue contains messages, then -RTEMS returns these message buffers back to the system message -buffer pool. The QCB for this queue as well as the memory for -the message buffers is reclaimed by RTEMS. - -**NOTES:** - -The calling task will be preempted if its preemption -mode is enabled and one or more local tasks with a higher -priority than the calling task are waiting on the deleted queue. -The calling task will NOT be preempted if the tasks that are -waiting are remote tasks. - -The calling task does not have to be the task that -created the queue, although the task and queue must reside on -the same node. - -When the queue is deleted, any messages in the queue -are returned to the free message buffer pool. Any information -stored in those messages is lost. - -When a global message queue is deleted, the message -queue id must be transmitted to every node in the system for -deletion from the local copy of the global object table. - -Proxies, used to represent remote tasks, are -reclaimed when the message queue is deleted. - -MESSAGE_QUEUE_SEND - Put message at rear of a queue ---------------------------------------------------- -.. index:: send message to a queue - -**CALLING SEQUENCE:** - -.. code:: c - - procedure Message_Queue_Send ( - ID : in RTEMS.ID; - Buffer : in RTEMS.Address; - Size : in RTEMS.Unsigned32; - Result : out RTEMS.Status_Codes - ); - -**DIRECTIVE STATUS CODES:** - -``RTEMS.SUCCESSFUL`` - message sent successfully -``RTEMS.INVALID_ID`` - invalid queue id -``RTEMS.INVALID_SIZE`` - invalid message size -``RTEMS.INVALID_ADDRESS`` - ``buffer`` is NULL -``RTEMS.UNSATISFIED`` - out of message buffers -``RTEMS.TOO_MANY`` - queue’s limit has been reached - -**DESCRIPTION:** - -This directive sends the message buffer of size bytes -in length to the queue specified by id. If a task is waiting at -the queue, then the message is copied to the waiting task’s -buffer and the task is unblocked. If no tasks are waiting at the -queue, then the message is copied to a message buffer which is -obtained from this message queue’s message buffer pool. The -message buffer is then placed at the rear of the queue. - -**NOTES:** - -The calling task will be preempted if it has -preemption enabled and a higher priority task is unblocked as -the result of this directive. - -Sending a message to a global message queue which -does not reside on the local node will generate a request to the -remote node to post the message on the specified message queue. - -If the task to be unblocked resides on a different -node from the message queue, then the message is forwarded to -the appropriate node, the waiting task is unblocked, and the -proxy used to represent the task is reclaimed. - -MESSAGE_QUEUE_URGENT - Put message at front of a queue ------------------------------------------------------- -.. index:: put message at front of queue - -**CALLING SEQUENCE:** - -.. code:: c - - procedure Message_Queue_Urgent ( - ID : in RTEMS.ID; - Buffer : in RTEMS.Address; - Size : in RTEMS.Unsigned32; - Result : out RTEMS.Status_Codes - ); - -**DIRECTIVE STATUS CODES:** - -``RTEMS.SUCCESSFUL`` - message sent successfully -``RTEMS.INVALID_ID`` - invalid queue id -``RTEMS.INVALID_SIZE`` - invalid message size -``RTEMS.INVALID_ADDRESS`` - ``buffer`` is NULL -``RTEMS.UNSATISFIED`` - out of message buffers -``RTEMS.TOO_MANY`` - queue’s limit has been reached - -**DESCRIPTION:** - -This directive sends the message buffer of size bytes -in length to the queue specified by id. If a task is waiting on -the queue, then the message is copied to the task’s buffer and -the task is unblocked. If no tasks are waiting on the queue, -then the message is copied to a message buffer which is obtained -from this message queue’s message buffer pool. The message -buffer is then placed at the front of the queue. - -**NOTES:** - -The calling task will be preempted if it has -preemption enabled and a higher priority task is unblocked as -the result of this directive. - -Sending a message to a global message queue which -does not reside on the local node will generate a request -telling the remote node to post the message on the specified -message queue. - -If the task to be unblocked resides on a different -node from the message queue, then the message is forwarded to -the appropriate node, the waiting task is unblocked, and the -proxy used to represent the task is reclaimed. - -MESSAGE_QUEUE_BROADCAST - Broadcast N messages to a queue ---------------------------------------------------------- -.. index:: broadcast message to a queue - -**CALLING SEQUENCE:** - -.. code:: c - - procedure Message_Queue_Broadcast ( - ID : in RTEMS.ID; - Buffer : in RTEMS.Address; - Size : in RTEMS.Unsigned32; - Count : out RTEMS.Unsigned32; - Result : out RTEMS.Status_Codes - ); - -**DIRECTIVE STATUS CODES:** - -``RTEMS.SUCCESSFUL`` - message broadcasted successfully -``RTEMS.INVALID_ID`` - invalid queue id -``RTEMS.INVALID_ADDRESS`` - ``buffer`` is NULL -``RTEMS.INVALID_ADDRESS`` - ``count`` is NULL -``RTEMS.INVALID_SIZE`` - invalid message size - -**DESCRIPTION:** - -This directive causes all tasks that are waiting at -the queue specified by id to be unblocked and sent the message -contained in buffer. Before a task is unblocked, the message -buffer of size byes in length is copied to that task’s message -buffer. The number of tasks that were unblocked is returned in -count. - -**NOTES:** - -The calling task will be preempted if it has -preemption enabled and a higher priority task is unblocked as -the result of this directive. - -The execution time of this directive is directly -related to the number of tasks waiting on the message queue, -although it is more efficient than the equivalent number of -invocations of ``rtems.message_queue_send``. - -Broadcasting a message to a global message queue -which does not reside on the local node will generate a request -telling the remote node to broadcast the message to the -specified message queue. - -When a task is unblocked which resides on a different -node from the message queue, a copy of the message is forwarded -to the appropriate node, the waiting task is unblocked, and the -proxy used to represent the task is reclaimed. - -MESSAGE_QUEUE_RECEIVE - Receive message from a queue ----------------------------------------------------- -.. index:: receive message from a queue - -**CALLING SEQUENCE:** - -.. code:: c - - procedure Message_Queue_Receive ( - ID : in RTEMS.ID; - Buffer : in RTEMS.Address; - Option_Set : in RTEMS.Option; - Timeout : in RTEMS.Interval; - Size : out RTEMS.Unsigned32; - Result : out RTEMS.Status_Codes - ); - -**DIRECTIVE STATUS CODES:** - -``RTEMS.SUCCESSFUL`` - message received successfully -``RTEMS.INVALID_ID`` - invalid queue id -``RTEMS.INVALID_ADDRESS`` - ``buffer`` is NULL -``RTEMS.INVALID_ADDRESS`` - ``size`` is NULL -``RTEMS.UNSATISFIED`` - queue is empty -``RTEMS.TIMEOUT`` - timed out waiting for message -``RTEMS.OBJECT_WAS_DELETED`` - queue deleted while waiting - -**DESCRIPTION:** - -This directive receives a message from the message -queue specified in id. The ``RTEMS.WAIT`` and ``RTEMS.NO_WAIT`` options of the -options parameter allow the calling task to specify whether to -wait for a message to become available or return immediately. -For either option, if there is at least one message in the -queue, then it is copied to buffer, size is set to return the -length of the message in bytes, and this directive returns -immediately with a successful return code. The buffer has to be big enough to -receive a message of the maximum length with respect to this message queue. - -If the calling task chooses to return immediately and -the queue is empty, then a status code indicating this condition -is returned. If the calling task chooses to wait at the message -queue and the queue is empty, then the calling task is placed on -the message wait queue and blocked. If the queue was created -with the ``RTEMS.PRIORITY`` option specified, then -the calling task is inserted into the wait queue according to -its priority. But, if the queue was created with the``RTEMS.FIFO`` option specified, then the -calling task is placed at the rear of the wait queue. - -A task choosing to wait at the queue can optionally -specify a timeout value in the timeout parameter. The timeout -parameter specifies the maximum interval to wait before the -calling task desires to be unblocked. If it is set to``RTEMS.NO_TIMEOUT``, then the calling task will wait forever. - -**NOTES:** - -The following message receive option constants are -defined by RTEMS: - -- ``RTEMS.WAIT`` - task will wait for a message (default) - -- ``RTEMS.NO_WAIT`` - task should not wait - -Receiving a message from a global message queue which -does not reside on the local node will generate a request to the -remote node to obtain a message from the specified message -queue. If no message is available and ``RTEMS.WAIT`` was specified, then -the task must be blocked until a message is posted. A proxy is -allocated on the remote node to represent the task until the -message is posted. - -A clock tick is required to support the timeout functionality of -this directive. - -MESSAGE_QUEUE_GET_NUMBER_PENDING - Get number of messages pending on a queue ----------------------------------------------------------------------------- -.. index:: get number of pending messages - -**CALLING SEQUENCE:** - -.. code:: c - - procedure Message_Queue_Get_Number_Pending ( - ID : in RTEMS.ID; - Count : out RTEMS.Unsigned32; - Result : out RTEMS.Status_Codes - ); - -**DIRECTIVE STATUS CODES:** - -``RTEMS.SUCCESSFUL`` - number of messages pending returned successfully -``RTEMS.INVALID_ADDRESS`` - ``count`` is NULL -``RTEMS.INVALID_ID`` - invalid queue id - -**DESCRIPTION:** - -This directive returns the number of messages pending on this -message queue in count. If no messages are present -on the queue, count is set to zero. - -**NOTES:** - -Getting the number of pending messages on a global message queue which -does not reside on the local node will generate a request to the -remote node to actually obtain the pending message count for -the specified message queue. - -MESSAGE_QUEUE_FLUSH - Flush all messages on a queue ---------------------------------------------------- -.. index:: flush messages on a queue - -**CALLING SEQUENCE:** - -.. code:: c - - procedure Message_Queue_Flush ( - ID : in RTEMS.ID; - Count : out RTEMS.Unsigned32; - Result : out RTEMS.Status_Codes - ); - -**DIRECTIVE STATUS CODES:** - -``RTEMS.SUCCESSFUL`` - message queue flushed successfully -``RTEMS.INVALID_ADDRESS`` - ``count`` is NULL -``RTEMS.INVALID_ID`` - invalid queue id - -**DESCRIPTION:** - -This directive removes all pending messages from the -specified queue id. The number of messages removed is returned -in count. If no messages are present on the queue, count is set -to zero. - -**NOTES:** - -Flushing all messages on a global message queue which -does not reside on the local node will generate a request to the -remote node to actually flush the specified message queue. - -.. COMMENT: COPYRIGHT (c) 1988-2002. - -.. COMMENT: On-Line Applications Research Corporation (OAR). - -.. COMMENT: All rights reserved. - |