From c9aaf3145fc84b55191c460f645985b814994d70 Mon Sep 17 00:00:00 2001 From: Chris Johns Date: Thu, 4 Feb 2016 10:19:13 +1300 Subject: Clean up --- c_user/multiprocessing.rst | 667 +++++++++++++++++++++------------------------ 1 file changed, 315 insertions(+), 352 deletions(-) (limited to 'c_user/multiprocessing.rst') diff --git a/c_user/multiprocessing.rst b/c_user/multiprocessing.rst index 1c0ba04..6bb3f12 100644 --- a/c_user/multiprocessing.rst +++ b/c_user/multiprocessing.rst @@ -1,3 +1,7 @@ +.. COMMENT: COPYRIGHT (c) 1988-2008. +.. COMMENT: On-Line Applications Research Corporation (OAR). +.. COMMENT: All rights reserved. + Multiprocessing Manager ####################### @@ -6,255 +10,233 @@ Multiprocessing Manager 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 +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. +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. + +The directives provided by the Manager are: + +- rtems_multiprocessing_announce_ - A multiprocessing communications packet has + arrived 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. +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. +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 +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. +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. +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 +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. +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. +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 +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: + +.. list-table:: + :class: rtems-table + + * - 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: @@ -270,153 +252,144 @@ A packet is sent by RTEMS in each of the following situations: - 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. +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 +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 + 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 +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: +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 + 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. +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) +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: +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 + 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. +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: +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 + 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 +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: +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 + 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. +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. +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 +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. +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: +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 @@ -426,9 +399,10 @@ Little endian byte-ordering is shown below: | | | | | +---------------+----------------+---------------+----------------+ -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: +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 +---------------+----------------+---------------+----------------+ @@ -437,47 +411,45 @@ endian processors. Big endian byte-ordering is shown below: | | | | | +---------------+----------------+---------------+----------------+ -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: +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. +- 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. +- 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. +- RTEMS makes no assumptions regarding the application data component of the + packet. Operations ========== @@ -485,19 +457,19 @@ 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. +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. +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. + +.. _rtems_multiprocessing_announce: MULTIPROCESSING_ANNOUNCE - Announce the arrival of a packet ----------------------------------------------------------- @@ -517,23 +489,14 @@ 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. +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 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. - -- cgit v1.2.3