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diff --git a/ada_user/multiprocessing_manager.rst b/ada_user/multiprocessing_manager.rst deleted file mode 100644 index a4d8d71..0000000 --- a/ada_user/multiprocessing_manager.rst +++ /dev/null @@ -1,548 +0,0 @@ -Multiprocessing Manager -####################### - -.. index:: multiprocessing - -Introduction -============ - -In multiprocessor real-time systems, new -requirements, such as sharing data and global resources between -processors, are introduced. This requires an efficient and -reliable communications vehicle which allows all processors to -communicate with each other as necessary. In addition, the -ramifications of multiple processors affect each and every -characteristic of a real-time system, almost always making them -more complicated. - -RTEMS addresses these issues by providing simple and -flexible real-time multiprocessing capabilities. The executive -easily lends itself to both tightly-coupled and loosely-coupled -configurations of the target system hardware. In addition, -RTEMS supports systems composed of both homogeneous and -heterogeneous mixtures of processors and target boards. - -A major design goal of the RTEMS executive was to -transcend the physical boundaries of the target hardware -configuration. This goal is achieved by presenting the -application software with a logical view of the target system -where the boundaries between processor nodes are transparent. -As a result, the application developer may designate objects -such as tasks, queues, events, signals, semaphores, and memory -blocks as global objects. These global objects may then be -accessed by any task regardless of the physical location of the -object and the accessing task. RTEMS automatically determines -that the object being accessed resides on another processor and -performs the actions required to access the desired object. -Simply stated, RTEMS allows the entire system, both hardware and -software, to be viewed logically as a single system. - -Multiprocessing operations are transparent at the application level. -Operations on remote objects are implicitly processed as remote -procedure calls. Although remote operations on objects are supported -from Ada tasks, the calls used to support the multiprocessing -communications should be implemented in C and are not supported -in the Ada binding. Since there is no Ada binding for RTEMS -multiprocessing support services, all examples and data structures -shown in this chapter are in C. - -Background -========== - -.. index:: multiprocessing topologies - -RTEMS makes no assumptions regarding the connection -media or topology of a multiprocessor system. The tasks which -compose a particular application can be spread among as many -processors as needed to satisfy the application’s timing -requirements. The application tasks can interact using a subset -of the RTEMS directives as if they were on the same processor. -These directives allow application tasks to exchange data, -communicate, and synchronize regardless of which processor they -reside upon. - -The RTEMS multiprocessor execution model is multiple -instruction streams with multiple data streams (MIMD). This -execution model has each of the processors executing code -independent of the other processors. Because of this -parallelism, the application designer can more easily guarantee -deterministic behavior. - -By supporting heterogeneous environments, RTEMS -allows the systems designer to select the most efficient -processor for each subsystem of the application. Configuring -RTEMS for a heterogeneous environment is no more difficult than -for a homogeneous one. In keeping with RTEMS philosophy of -providing transparent physical node boundaries, the minimal -heterogeneous processing required is isolated in the MPCI layer. - -Nodes ------ -.. index:: nodes, definition - -A processor in a RTEMS system is referred to as a -node. Each node is assigned a unique non-zero node number by -the application designer. RTEMS assumes that node numbers are -assigned consecutively from one to the ``maximum_nodes`` -configuration parameter. The node -number, node, and the maximum number of nodes, maximum_nodes, in -a system are found in the Multiprocessor Configuration Table. -The maximum_nodes field and the number of global objects, -maximum_global_objects, is required to be the same on all nodes -in a system. - -The node number is used by RTEMS to identify each -node when performing remote operations. Thus, the -Multiprocessor Communications Interface Layer (MPCI) must be -able to route messages based on the node number. - -Global Objects --------------- -.. index:: global objects, definition - -All RTEMS objects which are created with the GLOBAL -attribute will be known on all other nodes. Global objects can -be referenced from any node in the system, although certain -directive specific restrictions (e.g. one cannot delete a remote -object) may apply. A task does not have to be global to perform -operations involving remote objects. The maximum number of -global objects is the system is user configurable and can be -found in the maximum_global_objects field in the Multiprocessor -Configuration Table. The distribution of tasks to processors is -performed during the application design phase. Dynamic task -relocation is not supported by RTEMS. - -Global Object Table -------------------- -.. index:: global objects table - -RTEMS maintains two tables containing object -information on every node in a multiprocessor system: a local -object table and a global object table. The local object table -on each node is unique and contains information for all objects -created on this node whether those objects are local or global. -The global object table contains information regarding all -global objects in the system and, consequently, is the same on -every node. - -Since each node must maintain an identical copy of -the global object table, the maximum number of entries in each -copy of the table must be the same. The maximum number of -entries in each copy is determined by the -maximum_global_objects parameter in the Multiprocessor -Configuration Table. This parameter, as well as the -maximum_nodes parameter, is required to be the same on all -nodes. To maintain consistency among the table copies, every -node in the system must be informed of the creation or deletion -of a global object. - -Remote Operations ------------------ -.. index:: MPCI and remote operations - -When an application performs an operation on a remote -global object, RTEMS must generate a Remote Request (RQ) message -and send it to the appropriate node. After completing the -requested operation, the remote node will build a Remote -Response (RR) message and send it to the originating node. -Messages generated as a side-effect of a directive (such as -deleting a global task) are known as Remote Processes (RP) and -do not require the receiving node to respond. - -Other than taking slightly longer to execute -directives on remote objects, the application is unaware of the -location of the objects it acts upon. The exact amount of -overhead required for a remote operation is dependent on the -media connecting the nodes and, to a lesser degree, on the -efficiency of the user-provided MPCI routines. - -The following shows the typical transaction sequence -during a remote application: - -# The application issues a directive accessing a - remote global object. - -# RTEMS determines the node on which the object - resides. - -# RTEMS calls the user-provided MPCI routine - GET_PACKET to obtain a packet in which to build a RQ message. - -# After building a message packet, RTEMS calls the - user-provided MPCI routine SEND_PACKET to transmit the packet to - the node on which the object resides (referred to as the - destination node). - -# The calling task is blocked until the RR message - arrives, and control of the processor is transferred to another - task. - -# The MPCI layer on the destination node senses the - arrival of a packet (commonly in an ISR), and calls the``rtems_multiprocessing_announce`` - directive. This directive readies the Multiprocessing Server. - -# The Multiprocessing Server calls the user-provided - MPCI routine RECEIVE_PACKET, performs the requested operation, - builds an RR message, and returns it to the originating node. - -# The MPCI layer on the originating node senses the - arrival of a packet (typically via an interrupt), and calls the RTEMS``rtems_multiprocessing_announce`` directive. This directive - readies the Multiprocessing Server. - -# The Multiprocessing Server calls the user-provided - MPCI routine RECEIVE_PACKET, readies the original requesting - task, and blocks until another packet arrives. Control is - transferred to the original task which then completes processing - of the directive. - -If an uncorrectable error occurs in the user-provided -MPCI layer, the fatal error handler should be invoked. RTEMS -assumes the reliable transmission and reception of messages by -the MPCI and makes no attempt to detect or correct errors. - -Proxies -------- -.. index:: proxy, definition - -A proxy is an RTEMS data structure which resides on a -remote node and is used to represent a task which must block as -part of a remote operation. This action can occur as part of the``rtems.semaphore_obtain`` and``rtems.message_queue_receive`` directives. If the -object were local, the task’s control block would be available -for modification to indicate it was blocking on a message queue -or semaphore. However, the task’s control block resides only on -the same node as the task. As a result, the remote node must -allocate a proxy to represent the task until it can be readied. - -The maximum number of proxies is defined in the -Multiprocessor Configuration Table. Each node in a -multiprocessor system may require a different number of proxies -to be configured. The distribution of proxy control blocks is -application dependent and is different from the distribution of -tasks. - -Multiprocessor Configuration Table ----------------------------------- - -The Multiprocessor Configuration Table contains -information needed by RTEMS when used in a multiprocessor -system. This table is discussed in detail in the section -Multiprocessor Configuration Table of the Configuring a System -chapter. - -Multiprocessor Communications Interface Layer -============================================= - -The Multiprocessor Communications Interface Layer -(MPCI) is a set of user-provided procedures which enable the -nodes in a multiprocessor system to communicate with one -another. These routines are invoked by RTEMS at various times -in the preparation and processing of remote requests. -Interrupts are enabled when an MPCI procedure is invoked. It is -assumed that if the execution mode and/or interrupt level are -altered by the MPCI layer, that they will be restored prior to -returning to RTEMS... index:: MPCI, definition - -The MPCI layer is responsible for managing a pool of -buffers called packets and for sending these packets between -system nodes. Packet buffers contain the messages sent between -the nodes. Typically, the MPCI layer will encapsulate the -packet within an envelope which contains the information needed -by the MPCI layer. The number of packets available is dependent -on the MPCI layer implementation... index:: MPCI entry points - -The entry points to the routines in the user’s MPCI -layer should be placed in the Multiprocessor Communications -Interface Table. The user must provide entry points for each of -the following table entries in a multiprocessor system: - -- initialization initialize the MPCI - -- get_packet obtain a packet buffer - -- return_packet return a packet buffer - -- send_packet send a packet to another node - -- receive_packet called to get an arrived packet - -A packet is sent by RTEMS in each of the following situations: - -- an RQ is generated on an originating node; - -- an RR is generated on a destination node; - -- a global object is created; - -- a global object is deleted; - -- a local task blocked on a remote object is deleted; - -- during system initialization to check for system consistency. - -If the target hardware supports it, the arrival of a -packet at a node may generate an interrupt. Otherwise, the -real-time clock ISR can check for the arrival of a packet. In -any case, the``rtems_multiprocessing_announce`` directive must be called -to announce the arrival of a packet. After exiting the ISR, -control will be passed to the Multiprocessing Server to process -the packet. The Multiprocessing Server will call the get_packet -entry to obtain a packet buffer and the receive_entry entry to -copy the message into the buffer obtained. - -INITIALIZATION --------------- - -The INITIALIZATION component of the user-provided -MPCI layer is called as part of the ``rtems_initialize_executive`` -directive to initialize the MPCI layer and associated hardware. -It is invoked immediately after all of the device drivers have -been initialized. This component should be adhere to the -following prototype:.. index:: rtems_mpci_entry - -.. code:: c - - rtems_mpci_entry user_mpci_initialization( - rtems_configuration_table \*configuration - ); - -where configuration is the address of the user’s -Configuration Table. Operations on global objects cannot be -performed until this component is invoked. The INITIALIZATION -component is invoked only once in the life of any system. If -the MPCI layer cannot be successfully initialized, the fatal -error manager should be invoked by this routine. - -One of the primary functions of the MPCI layer is to -provide the executive with packet buffers. The INITIALIZATION -routine must create and initialize a pool of packet buffers. -There must be enough packet buffers so RTEMS can obtain one -whenever needed. - -GET_PACKET ----------- - -The GET_PACKET component of the user-provided MPCI -layer is called when RTEMS must obtain a packet buffer to send -or broadcast a message. This component should be adhere to the -following prototype: -.. code:: c - - rtems_mpci_entry user_mpci_get_packet( - rtems_packet_prefix \**packet - ); - -where packet is the address of a pointer to a packet. -This routine always succeeds and, upon return, packet will -contain the address of a packet. If for any reason, a packet -cannot be successfully obtained, then the fatal error manager -should be invoked. - -RTEMS has been optimized to avoid the need for -obtaining a packet each time a message is sent or broadcast. -For example, RTEMS sends response messages (RR) back to the -originator in the same packet in which the request message (RQ) -arrived. - -RETURN_PACKET -------------- - -The RETURN_PACKET component of the user-provided MPCI -layer is called when RTEMS needs to release a packet to the free -packet buffer pool. This component should be adhere to the -following prototype: -.. code:: c - - rtems_mpci_entry user_mpci_return_packet( - rtems_packet_prefix \*packet - ); - -where packet is the address of a packet. If the -packet cannot be successfully returned, the fatal error manager -should be invoked. - -RECEIVE_PACKET --------------- - -The RECEIVE_PACKET component of the user-provided -MPCI layer is called when RTEMS needs to obtain a packet which -has previously arrived. This component should be adhere to the -following prototype: -.. code:: c - - rtems_mpci_entry user_mpci_receive_packet( - rtems_packet_prefix \**packet - ); - -where packet is a pointer to the address of a packet -to place the message from another node. If a message is -available, then packet will contain the address of the message -from another node. If no messages are available, this entry -packet should contain NULL. - -SEND_PACKET ------------ - -The SEND_PACKET component of the user-provided MPCI -layer is called when RTEMS needs to send a packet containing a -message to another node. This component should be adhere to the -following prototype: -.. code:: c - - rtems_mpci_entry user_mpci_send_packet( - uint32_t node, - rtems_packet_prefix \**packet - ); - -where node is the node number of the destination and packet is the -address of a packet which containing a message. If the packet cannot -be successfully sent, the fatal error manager should be invoked. - -If node is set to zero, the packet is to be -broadcasted to all other nodes in the system. Although some -MPCI layers will be built upon hardware which support a -broadcast mechanism, others may be required to generate a copy -of the packet for each node in the system. - -.. COMMENT: XXX packet_prefix structure needs to be defined in this document - -Many MPCI layers use the ``packet_length`` field of the``rtems_packet_prefix`` portion -of the packet to avoid sending unnecessary data. This is especially -useful if the media connecting the nodes is relatively slow. - -The ``to_convert`` field of the ``rtems_packet_prefix`` portion of the -packet indicates how much of the packet in 32-bit units may require conversion -in a heterogeneous system. - -Supporting Heterogeneous Environments -------------------------------------- -.. index:: heterogeneous multiprocessing - -Developing an MPCI layer for a heterogeneous system -requires a thorough understanding of the differences between the -processors which comprise the system. One difficult problem is -the varying data representation schemes used by different -processor types. The most pervasive data representation problem -is the order of the bytes which compose a data entity. -Processors which place the least significant byte at the -smallest address are classified as little endian processors. -Little endian byte-ordering is shown below: - -.. code:: c - - +---------------+----------------+---------------+----------------+ - | | | | | - | Byte 3 | Byte 2 | Byte 1 | Byte 0 | - | | | | | - +---------------+----------------+---------------+----------------+ - -Conversely, processors which place the most -significant byte at the smallest address are classified as big -endian processors. Big endian byte-ordering is shown below: -.. code:: c - - +---------------+----------------+---------------+----------------+ - | | | | | - | Byte 0 | Byte 1 | Byte 2 | Byte 3 | - | | | | | - +---------------+----------------+---------------+----------------+ - -Unfortunately, sharing a data structure between big -endian and little endian processors requires translation into a -common endian format. An application designer typically chooses -the common endian format to minimize conversion overhead. - -Another issue in the design of shared data structures -is the alignment of data structure elements. Alignment is both -processor and compiler implementation dependent. For example, -some processors allow data elements to begin on any address -boundary, while others impose restrictions. Common restrictions -are that data elements must begin on either an even address or -on a long word boundary. Violation of these restrictions may -cause an exception or impose a performance penalty. - -Other issues which commonly impact the design of -shared data structures include the representation of floating -point numbers, bit fields, decimal data, and character strings. -In addition, the representation method for negative integers -could be one’s or two’s complement. These factors combine to -increase the complexity of designing and manipulating data -structures shared between processors. - -RTEMS addressed these issues in the design of the -packets used to communicate between nodes. The RTEMS packet -format is designed to allow the MPCI layer to perform all -necessary conversion without burdening the developer with the -details of the RTEMS packet format. As a result, the MPCI layer -must be aware of the following: - -- All packets must begin on a four byte boundary. - -- Packets are composed of both RTEMS and application data. All RTEMS data - is treated as 32-bit unsigned quantities and is in the first ``to_convert`` - 32-bit quantities of the packet. The ``to_convert`` field is part of the``rtems_packet_prefix`` portion of the packet. - -- The RTEMS data component of the packet must be in native - endian format. Endian conversion may be performed by either the - sending or receiving MPCI layer. - -- RTEMS makes no assumptions regarding the application - data component of the packet. - -Operations -========== - -Announcing a Packet -------------------- - -The ``rtems_multiprocessing_announce`` directive is called by -the MPCI layer to inform RTEMS that a packet has arrived from -another node. This directive can be called from an interrupt -service routine or from within a polling routine. - -Directives -========== - -This section details the additional directives -required to support RTEMS in a multiprocessor configuration. A -subsection is dedicated to each of this manager’s directives and -describes the calling sequence, related constants, usage, and -status codes. - -MULTIPROCESSING_ANNOUNCE - Announce the arrival of a packet ------------------------------------------------------------ -.. index:: announce arrival of package - -**CALLING SEQUENCE:** - -.. index:: rtems_multiprocessing_announce - -.. code:: c - - void rtems_multiprocessing_announce( void ); - -**DIRECTIVE STATUS CODES:** - -NONE - -**DESCRIPTION:** - -This directive informs RTEMS that a multiprocessing -communications packet has arrived from another node. This -directive is called by the user-provided MPCI, and is only used -in multiprocessor configurations. - -**NOTES:** - -This directive is typically called from an ISR. - -This directive will almost certainly cause the -calling task to be preempted. - -This directive does not generate activity on remote nodes. - -.. COMMENT: COPYRIGHT (c) 2014. - -.. COMMENT: On-Line Applications Research Corporation (OAR). - -.. COMMENT: All rights reserved. - |