@c @c COPYRIGHT (c) 1988-1998. @c On-Line Applications Research Corporation (OAR). @c All rights reserved. @c @c $Id$ @c @ifinfo @node Configuring a System, Configuring a System Configuration Table, EXTENSION_DELETE - Delete a extension set, Top @end ifinfo @chapter Configuring a System @ifinfo @menu * Configuring a System Configuration Table:: * Configuring a System RTEMS API Configuration Table:: * Configuring a System POSIX API Configuration Table:: * Configuring a System CPU Dependent Information Table:: * Configuring a System Initialization Task Table:: * Configuring a System Driver Address Table:: * Configuring a System User Extensions Table:: * Configuring a System Multiprocessor Configuration Table:: * Configuring a System Multiprocessor Communications Interface Table:: * Configuring a System Determining Memory Requirements:: * Configuring a System Sizing the RTEMS RAM Workspace:: @end menu @end ifinfo @ifinfo @node Configuring a System Configuration Table, Configuring a System RTEMS API Configuration Table, Configuring a System, Configuring a System @end ifinfo @section Configuration Table The RTEMS Configuration Table is used to tailor an application for its specific needs. For example, the user can configure the number of device drivers or which APIs may be used. THe address of the user-defined Configuration Table is passed as an argument to the initialize_executive directive, which MUST be the first RTEMS directive called. The RTEMS Configuration Table is defined in the following @value{LANGUAGE} @value{STRUCTURE}: @ifset is-C @example @group typedef struct @{ void *work_space_start; rtems_unsigned32 work_space_size; rtems_unsigned32 maximum_extensions; rtems_unsigned32 microseconds_per_tick; rtems_unsigned32 ticks_per_timeslice; rtems_unsigned32 maximum_devices; rtems_unsigned32 number_of_device_drivers; rtems_driver_address_table *Device_driver_table; rtems_extensions_table *User_extension_table; rtems_multiprocessing_table *User_multiprocessing_table; rtems_api_configuration_table *RTEMS_api_configuration; posix_api_configuration_table *POSIX_api_configuration; @} rtems_configuration_table; @end group @end example @end ifset @ifset is-Ada @example type Configuration_Table is record Work_Space_Start : RTEMS.Address; Work_Space_Size : RTEMS.Unsigned32; Maximum_Extensions : RTEMS.Unsigned32; Microseconds_Per_Tick : RTEMS.Unsigned32; Ticks_Per_Timeslice : RTEMS.Unsigned32; Maximum_Devices : RTEMS.Unsigned32; Number_Of_Device_Drivers : RTEMS.Unsigned32; Device_Driver_Table : RTEMS.Driver_Address_Table_Pointer; User_Extension_Table : RTEMS.Extensions_Table_Pointer; User_Multiprocessing_Table : RTEMS.Multiprocessing_Table_Pointer; RTEMS_API_Configuration : RTEMS.API_Configuration_Table_Pointer; POSIX_API_Configuration : RTEMS.POSIX_API_Configuration_Table_Pointer; end record; type Configuration_Table_Pointer is access all Configuration_Table; @end example @end ifset @table @b @item work_space_start is the address of the RTEMS RAM Workspace. This area contains items such as the various object control blocks (TCBs, QCBs, ...) and task stacks. If the address is not aligned on a four-word boundary, then RTEMS will invoke the fatal error handler during initialize_executive. @item work_space_size is the calculated size of the RTEMS RAM Workspace. The section Sizing the RTEMS RAM Workspace details how to arrive at this number. @item microseconds_per_tick is number of microseconds per clock tick. @item ticks_per_timeslice is the number of clock ticks for a timeslice. @item maximum_devices is the maximum number of devices that can be registered. @item number_of_device_drivers is the number of device drivers for the system. There should be the same number of entries in the Device Driver Table. If this field is zero, then the User_driver_address_table entry should be NULL. @item Device_driver_table is the address of the Device Driver Table. This table contains the entry points for each device driver. If the number_of_device_drivers field is zero, then this entry should be NULL. The format of this table will be discussed below. @item User_extension_table is the address of the User Extension Table. This table contains the entry points for the static set of optional user extensions. If no user extensions are configured, then this entry should be NULL. The format of this table will be discussed below. @item User_multiprocessing_table is the address of the Multiprocessor Configuration Table. This table contains information needed by RTEMS only when used in a multiprocessor configuration. This field must be NULL when RTEMS is used in a single processor configuration. @item RTEMS_api_configuration is the address of the RTEMS API Configuration Table. This table contains information needed by the RTEMS API. This field should be NULL if the RTEMS API is not used. [NOTE: Currently the RTEMS API is required to support support components such as BSPs and libraries which use this API.] @item POSIX_api_configuration is the address of the POSIX API Configuration Table. This table contains information needed by the POSIX API. This field should be NULL if the POSIX API is not used. @end table @ifinfo @node Configuring a System RTEMS API Configuration Table, Configuring a System POSIX API Configuration Table, Configuring a System Configuration Table, Configuring a System @end ifinfo @section RTEMS API Configuration Table The RTEMS API Configuration Table is used to configure the managers which constitute the RTEMS API for a particular application. For example, the user can configure the maximum number of tasks for this application. The RTEMS API Configuration Table is defined in the following @value{LANGUAGE} @value{STRUCTURE}: @ifset is-C @example @group typedef struct @{ rtems_unsigned32 maximum_tasks; rtems_unsigned32 maximum_timers; rtems_unsigned32 maximum_semaphores; rtems_unsigned32 maximum_message_queues; rtems_unsigned32 maximum_partitions; rtems_unsigned32 maximum_regions; rtems_unsigned32 maximum_ports; rtems_unsigned32 maximum_periods; rtems_unsigned32 number_of_initialization_tasks; rtems_initialization_tasks_table *User_initialization_tasks_table; @} rtems_api_configuration_table; @end group @end example @end ifset @ifset is-Ada @example type API_Configuration_Table is record Maximum_Tasks : RTEMS.Unsigned32; Maximum_Timers : RTEMS.Unsigned32; Maximum_Semaphores : RTEMS.Unsigned32; Maximum_Message_queues : RTEMS.Unsigned32; Maximum_Partitions : RTEMS.Unsigned32; Maximum_Regions : RTEMS.Unsigned32; Maximum_Ports : RTEMS.Unsigned32; Maximum_Periods : RTEMS.Unsigned32; Number_Of_Initialization_Tasks : RTEMS.Unsigned32; User_Initialization_Tasks_Table : RTEMS.Initialization_Tasks_Table_Pointer; end record; type API_Configuration_Table_Pointer is access all API_Configuration_Table; @end example @end ifset @table @b @item maximum_tasks is the maximum number of tasks that can be concurrently active (created) in the system including initialization tasks. @item maximum_timers is the maximum number of timers that can be concurrently active in the system. @item maximum_semaphores is the maximum number of semaphores that can be concurrently active in the system. @item maximum_message_queues is the maximum number of message queues that can be concurrently active in the system. @item maximum_partitions is the maximum number of partitions that can be concurrently active in the system. @item maximum_regions is the maximum number of regions that can be concurrently active in the system. @item maximum_ports is the maximum number of ports into dual-port memory areas that can be concurrently active in the system. @item number_of_initialization_tasks is the number of initialization tasks configured. At least one initialization task must be configured. @item User_initialization_tasks_table is the address of the Initialization Task Table. This table contains the information needed to create and start each of the initialization tasks. The format of this table will be discussed below. @end table @ifinfo @node Configuring a System POSIX API Configuration Table, Configuring a System CPU Dependent Information Table, Configuring a System RTEMS API Configuration Table, Configuring a System @end ifinfo @section POSIX API Configuration Table The POSIX API Configuration Table is used to configure the managers which constitute the POSIX API for a particular application. For example, the user can configure the maximum number of threads for this application. The POSIX API Configuration Table is defined in the following @value{LANGUAGE} @value{STRUCTURE}: @ifset is-C @example @group typedef struct @{ void *(*thread_entry)(void *); @} posix_initialization_threads_table; typedef struct @{ int maximum_threads; int maximum_mutexes; int maximum_condition_variables; int maximum_keys; int maximum_queued_signals; int number_of_initialization_tasks; posix_initialization_threads_table *User_initialization_tasks_table; @} posix_api_configuration_table; @end group @end example @end ifset @ifset is-Ada @example type POSIX_Thread_Entry is access procedure ( Argument : in RTEMS.Address ); type POSIX_Initialization_Threads_Table_Entry is record Thread_Entry : RTEMS.POSIX_Thread_Entry; end record; type POSIX_Initialization_Threads_Table is array ( RTEMS.Unsigned32 range <> ) of RTEMS.POSIX_Initialization_Threads_Table_Entry; type POSIX_Initialization_Threads_Table_Pointer is access all POSIX_Initialization_Threads_Table; type POSIX_API_Configuration_Table_Entry is record Maximum_Threads : Interfaces.C.Int; Maximum_Mutexes : Interfaces.C.Int; Maximum_Condition_Variables : Interfaces.C.Int; Maximum_Keys : Interfaces.C.Int; Maximum_Queued_Signals : Interfaces.C.Int; Number_Of_Initialization_Tasks : Interfaces.C.Int; User_Initialization_Tasks_Table : RTEMS.POSIX_Initialization_Threads_Table_Pointer; end record; type POSIX_API_Configuration_Table is array ( RTEMS.Unsigned32 range <> ) of RTEMS.POSIX_API_Configuration_Table_Entry; type POSIX_API_Configuration_Table_Pointer is access all RTEMS.POSIX_API_Configuration_Table; @end example @end ifset @table @b @item maximum_threads is the maximum number of threads that can be concurrently active (created) in the system including initialization threads. @item maximum_mutexes is the maximum number of mutexes that can be concurrently active in the system. @item maximum_condition_variables is the maximum number of condition variables that can be concurrently active in the system. @item maximum_keys is the maximum number of keys that can be concurrently active in the system. @item maximum_queued_signals is the maximum number of queued signals that can be concurrently pending in the system. @item number_of_initialization_threads is the number of initialization threads configured. At least one initialization threads must be configured. @item User_initialization_threads_table is the address of the Initialization Threads Table. This table contains the information needed to create and start each of the initialization threads. The format of each entry in this table is defined in the posix_initialization_threads_table @value{STRUCTURE}. @end table @ifinfo @node Configuring a System CPU Dependent Information Table, Configuring a System Initialization Task Table, Configuring a System POSIX API Configuration Table, Configuring a System @end ifinfo @section CPU Dependent Information Table The CPU Dependent Information Table is used to describe processor dependent information required by RTEMS. This table is generally used to supply RTEMS with information only known by the Board Support Package. The contents of this table are discussed in the CPU Dependent Information Table chapter of the Applications Supplement document for a specific target processor. @ifinfo @node Configuring a System Initialization Task Table, Configuring a System Driver Address Table, Configuring a System CPU Dependent Information Table, Configuring a System @end ifinfo @section Initialization Task Table The Initialization Task Table is used to describe each of the user initialization tasks to the Initialization Manager. The table contains one entry for each initialization task the user wishes to create and start. The fields of this data structure directly correspond to arguments to the task_create and task_start directives. The number of entries is found in the number_of_initialization_tasks entry in the Configuration Table. The format of each entry in the Initialization Task Table is defined in the following @value{LANGUAGE} @value{STRUCTURE}: @ifset is-C @example typedef struct @{ rtems_name name; rtems_unsigned32 stack_size; rtems_task_priority initial_priority; rtems_attribute attribute_set; rtems_task_entry entry_point; rtems_mode mode_set; rtems_task_argument argument; @} rtems_initialization_tasks_table; @end example @end ifset @ifset is-Ada @example type Initialization_Tasks_Table_Entry is record Name : RTEMS.Name; -- task name Stack_Size : RTEMS.Unsigned32; -- task stack size Initial_Priority : RTEMS.Task_priority; -- task priority Attribute_Set : RTEMS.Attribute; -- task attributes Entry_Point : RTEMS.Task_Entry; -- task entry point Mode_Set : RTEMS.Mode; -- task initial mode Argument : RTEMS.Unsigned32; -- task argument end record; type Initialization_Tasks_Table is array ( RTEMS.Unsigned32 range <> ) of RTEMS.Initialization_Tasks_Table_Entry; type Initialization_Tasks_Table_Pointer is access all Initialization_Tasks_Table; @end example @end ifset @table @b @item name is the name of this initialization task. @item stack_size is the size of the stack for this initialization task. @item initial_priority is the priority of this initialization task. @item attribute_set is the attribute set used during creation of this initialization task. @item entry_point is the address of the entry point of this initialization task. @item mode_set is the initial execution mode of this initialization task. @item argument is the initial argument for this initialization task. @end table A typical declaration for an Initialization Task Table might appear as follows: @ifset is-C @example rtems_initialization_tasks_table Initialization_tasks[2] = @{ @{ INIT_1_NAME, 1024, 1, DEFAULT_ATTRIBUTES, Init_1, DEFAULT_MODES, 1 @}, @{ INIT_2_NAME, 1024, 250, FLOATING_POINT, Init_2, NO_PREEMPT, 2 @} @}; @end example @end ifset @ifset is-Ada @example Initialization_Tasks : aliased RTEMS.Initialization_Tasks_Table( 1 .. 2 ) := ( (INIT_1_NAME, 1024, 1, RTEMS.Default_Attributes, Init_1'Access, RTEMS.Default_Modes, 1), (INIT_2_NAME, 1024, 250, RTEMS.Floating_Point, Init_2'Access, RTEMS.No_Preempt, 2) ); @end example @end ifset @ifinfo @node Configuring a System Driver Address Table, Configuring a System User Extensions Table, Configuring a System Initialization Task Table, Configuring a System @end ifinfo @section Driver Address Table The Device Driver Table is used to inform the I/O Manager of the set of entry points for each device driver configured in the system. The table contains one entry for each device driver required by the application. The number of entries is defined in the number_of_device_drivers entry in the Configuration Table. The format of each entry in the Device Driver Table is defined in the following @value{LANGUAGE} @value{STRUCTURE}: @ifset is-C @example typedef struct @{ rtems_device_driver_entry initialization; rtems_device_driver_entry open; rtems_device_driver_entry close; rtems_device_driver_entry read; rtems_device_driver_entry write; rtems_device_driver_entry control; @} rtems_driver_address_table; @end example @end ifset @ifset is-Ada @example type Driver_Address_Table_Entry is record Initialization : RTEMS.Device_Driver_Entry; Open : RTEMS.Device_Driver_Entry; Close : RTEMS.Device_Driver_Entry; Read : RTEMS.Device_Driver_Entry; Write : RTEMS.Device_Driver_Entry; Control : RTEMS.Device_Driver_Entry; end record; type Driver_Address_Table is array ( RTEMS.Unsigned32 range <> ) of RTEMS.Driver_Address_Table_Entry; type Driver_Address_Table_Pointer is access all Driver_Address_Table; @end example @end ifset @table @b @item initialization is the address of the entry point called by io_initialize to initialize a device driver and its associated devices. @item open is the address of the entry point called by io_open. @item close is the address of the entry point called by io_close. @item read is the address of the entry point called by io_read. @item write is the address of the entry point called by io_write. @item control is the address of the entry point called by io_control. @end table Driver entry points configured as NULL will always return a status code of @code{SUCCESSFUL}. No user code will be executed in this situation. A typical declaration for a Device Driver Table might appear as follows: @ifset is-C @example rtems_driver_address_table Driver_table[2] = @{ @{ tty_initialize, tty_open, tty_close, /* major = 0 */ tty_read, tty_write, tty_control @}, @{ lp_initialize, lp_open, lp_close, /* major = 1 */ NULL, lp_write, lp_control @} @}; @end example @end ifset @ifset is-Ada @example @end example @end ifset More information regarding the construction and operation of device drivers is provided in the I/O Manager chapter. @ifinfo @node Configuring a System User Extensions Table, Configuring a System Multiprocessor Configuration Table, Configuring a System Driver Address Table, Configuring a System @end ifinfo @section User Extensions Table The User Extensions Table is used to inform RTEMS of the optional user-supplied static extension set. This table contains one entry for each possible extension. The entries are called at critical times in the life of the system and individual tasks. The application may create dynamic extensions in addition to this single static set. The format of each entry in the User Extensions Table is defined in the following @value{LANGUAGE} @value{STRUCTURE}: @ifset is-C @example typedef User_extensions_routine rtems_extension; typedef User_extensions_thread_create_extension rtems_task_create_extension; typedef User_extensions_thread_delete_extension rtems_task_delete_extension; typedef User_extensions_thread_start_extension rtems_task_start_extension; typedef User_extensions_thread_restart_extension rtems_task_restart_extension; typedef User_extensions_thread_switch_extension rtems_task_switch_extension; typedef User_extensions_thread_begin_extension rtems_task_begin_extension; typedef User_extensions_thread_exitted_extension rtems_task_exitted_extension; typedef User_extensions_fatal_extension rtems_fatal_extension; typedef User_extensions_Table rtems_extensions_table; typedef struct @{ rtems_task_create_extension thread_create; rtems_task_start_extension thread_start; rtems_task_restart_extension thread_restart; rtems_task_delete_extension thread_delete; rtems_task_switch_extension thread_switch; rtems_task_post_switch_extension thread_post_switch; rtems_task_begin_extension thread_begin; rtems_task_exitted_extension thread_exitted; rtems_fatal_extension fatal; @} User_extensions_Table; @end example @end ifset @ifset is-Ada @example type Extensions_Table_Entry is record Thread_Create : RTEMS.Thread_Create_Extension; Thread_Start : RTEMS.Thread_Start_Extension; Thread_Restart : RTEMS.Thread_Restart_Extension; Thread_Delete : RTEMS.Thread_Delete_Extension; Thread_Switch : RTEMS.Thread_Switch_Extension; Thread_Post_Switch : RTEMS.Thread_Post_Switch_Extension; Thread_Begin : RTEMS.Thread_Begin_Extension; Thread_Exitted : RTEMS.Thread_Exitted_Extension; Fatal : RTEMS.Fatal_Error_Extension; end record; @end example @end ifset @table @b @item thread_create is the address of the user-supplied subroutine for the TASK_CREATE extension. If this extension for task creation is defined, it is called from the task_create directive. A value of NULL indicates that no extension is provided. @item thread_start is the address of the user-supplied subroutine for the TASK_START extension. If this extension for task initiation is defined, it is called from the task_start directive. A value of NULL indicates that no extension is provided. @item thread_restart is the address of the user-supplied subroutine for the TASK_RESTART extension. If this extension for task re-initiation is defined, it is called from the task_restart directive. A value of NULL indicates that no extension is provided. @item thread_delete is the address of the user-supplied subroutine for the TASK_DELETE extension. If this RTEMS extension for task deletion is defined, it is called from the task_delete directive. A value of NULL indicates that no extension is provided. @item thread_switch is the address of the user-supplied subroutine for the task context switch extension. This subroutine is called from RTEMS dispatcher after the current task has been swapped out but before the new task has been swapped in. A value of NULL indicates that no extension is provided. As this routine is invoked after saving the current task's context and before restoring the heir task's context, it is not necessary for this routine to save and restore any registers. @item thread_post_switch is the address of the user-supplied subroutine for the post task context switch extension. This subroutine is called from RTEMS dispatcher in the context of the task which has just been swapped in. @item thread_begin is the address of the user-supplied subroutine which is invoked immediately before a task begins execution. It is invoked in the context of the beginning task. A value of NULL indicates that no extension is provided. @item thread_exitted is the address of the user-supplied subroutine which is invoked when a task exits. This procedure is responsible for some action which will allow the system to continue execution (i.e. delete or restart the task) or to terminate with a fatal error. If this field is set to NULL, the default RTEMS task_exitted handler will be invoked. @item fatal is the address of the user-supplied subroutine for the FATAL extension. This RTEMS extension of fatal error handling is called from the fatal_error_occurred directive. If the user's fatal error handler returns or if this entry is NULL then the default RTEMS fatal error handler will be executed. @end table A typical declaration for a User Extension Table which defines the TASK_CREATE, TASK_DELETE, TASK_SWITCH, and FATAL extension might appear as follows: @ifset is-C @example rtems_extensions_table User_extensions = @{ task_create_extension, NULL, NULL, task_delete_extension, task_switch_extension, NULL, NULL, fatal_extension @}; @end example @end ifset @ifset is-Ada User_Extensions : RTEMS.Extensions_Table := ( Task_Create_Extension'Access, null, null, Task_Delete_Extension'Access, Task_Switch_Extension'Access, null, null, Fatal_Extension'Access ); @example @end example @end ifset More information regarding the user extensions is provided in the User Extensions chapter. @ifinfo @node Configuring a System Multiprocessor Configuration Table, Configuring a System Multiprocessor Communications Interface Table, Configuring a System User Extensions Table, Configuring a System @end ifinfo @section Multiprocessor Configuration Table The Multiprocessor Configuration Table contains information needed when using RTEMS in a multiprocessor configuration. Many of the details associated with configuring a multiprocessor system are dependent on the multiprocessor communications layer provided by the user. The address of the Multiprocessor Configuration Table should be placed in the User_multiprocessing_table entry in the primary Configuration Table. Further details regarding many of the entries in the Multiprocessor Configuration Table will be provided in the Multiprocessing chapter. The format of the Multiprocessor Configuration Table is defined in the following @value{LANGUAGE} @value{STRUCTURE}: @ifset is-C @example typedef struct @{ rtems_unsigned32 node; rtems_unsigned32 maximum_nodes; rtems_unsigned32 maximum_global_objects; rtems_unsigned32 maximum_proxies; rtems_mpci_table *User_mpci_table; @} rtems_multiprocessing_table; @end example @end ifset @ifset is-Ada @example type Multiprocessing_Table is record Node : RTEMS.Unsigned32; Maximum_Nodes : RTEMS.Unsigned32; Maximum_Global_Objects : RTEMS.Unsigned32; Maximum_Proxies : RTEMS.Unsigned32; User_MPCI_Table : RTEMS.MPCI_Table_Pointer; end record; type Multiprocessing_Table_Pointer is access all Multiprocessing_Table; @end example @end ifset @table @b @item node is a unique processor identifier and is used in routing messages between nodes in a multiprocessor configuration. Each processor must have a unique node number. RTEMS assumes that node numbers start at one and increase sequentially. This assumption can be used to advantage by the user-supplied MPCI layer. Typically, this requirement is made when the node numbers are used to calculate the address of inter-processor communication links. Zero should be avoided as a node number because some MPCI layers use node zero to represent broadcasted packets. Thus, it is recommended that node numbers start at one and increase sequentially. @item maximum_nodes is the number of processor nodes in the system. @item maximum_global_objects is the maximum number of global objects which can exist at any given moment in the entire system. If this parameter is not the same on all nodes in the system, then a fatal error is generated to inform the user that the system is inconsistent. @item maximum_proxies is the maximum number of proxies which can exist at any given moment on this particular node. A proxy is a substitute task control block which represent a task residing on a remote node when that task blocks on a remote object. Proxies are used in situations in which delayed interaction is required with a remote node. @item User_mpci_table is the address of the Multiprocessor Communications Interface Table. This table contains the entry points of user-provided functions which constitute the multiprocessor communications layer. This table must be provided in multiprocessor configurations with all entries configured. The format of this table and details regarding its entries can be found in the next section. @end table @ifinfo @node Configuring a System Multiprocessor Communications Interface Table, Configuring a System Determining Memory Requirements, Configuring a System Multiprocessor Configuration Table, Configuring a System @end ifinfo @section Multiprocessor Communications Interface Table The format of this table is defined in the following @value{LANGUAGE} @value{STRUCTURE}: @ifset is-C @example typedef struct @{ rtems_unsigned32 default_timeout; /* in ticks */ rtems_unsigned32 maximum_packet_size; rtems_mpci_initialization_entry initialization; rtems_mpci_get_packet_entry get_packet; rtems_mpci_return_packet_entry return_packet; rtems_mpci_send_entry send; rtems_mpci_receive_entry receive; @} rtems_mpci_table; @end example @end ifset @ifset is-Ada @example type MPCI_Table is record Default_Timeout : RTEMS.Unsigned32; -- in ticks Maximum_Packet_Size : RTEMS.Unsigned32; Initialization : RTEMS.MPCI_Initialization_Entry; Get_Packet : RTEMS.MPCI_Get_Packet_Entry; Return_Packet : RTEMS.MPCI_Return_Packet_Entry; Send : RTEMS.MPCI_Send_Entry; Receive : RTEMS.MPCI_Receive_Entry; end record; type MPCI_Table_Pointer is access all MPCI_Table; @end example @end ifset @table @b @item default_timeout is the default maximum length of time a task should block waiting for a response to a directive which results in communication with a remote node. The maximum length of time is a function the user supplied multiprocessor communications layer and the media used. This timeout only applies to directives which would not block if the operation were performed locally. @item maximum_packet_size is the size in bytes of the longest packet which the MPCI layer is capable of sending. This value should represent the total number of bytes available for a RTEMS interprocessor messages. @item initialization is the address of the entry point for the initialization procedure of the user supplied multiprocessor communications layer. @item get_packet is the address of the entry point for the procedure called by RTEMS to obtain a packet from the user supplied multiprocessor communications layer. @item return_packet is the address of the entry point for the procedure called by RTEMS to return a packet to the user supplied multiprocessor communications layer. @item send is the address of the entry point for the procedure called by RTEMS to send an envelope to another node. This procedure is part of the user supplied multiprocessor communications layer. @item receive is the address of the entry point for the procedure called by RTEMS to retrieve an envelope containing a message from another node. This procedure is part of the user supplied multiprocessor communications layer. @end table More information regarding the required functionality of these entry points is provided in the Multiprocessor chapter. @ifinfo @node Configuring a System Determining Memory Requirements, Configuring a System Sizing the RTEMS RAM Workspace, Configuring a System Multiprocessor Communications Interface Table, Configuring a System @end ifinfo @section Determining Memory Requirements Since memory is a critical resource in many real-time embedded systems, RTEMS was specifically designed to allow unused managers to be excluded from the run-time environment. This allows the application designer the flexibility to tailor RTEMS to most efficiently meet system requirements while still satisfying even the most stringent memory constraints. As result, the size of the RTEMS executive is application dependent. A Memory Requirements worksheet is provided in the Applications Supplement document for a specific target processor. This worksheet can be used to calculate the memory requirements of a custom RTEMS run-time environment. To insure that enough memory is allocated for future versions of RTEMS, the application designer should round these memory requirements up. The following managers may be optionally excluded: @itemize @bullet @item signal @item region @item dual ported memory @item event @item multiprocessing @item partition @item timer @item semaphore @item message @item rate monotonic @end itemize RTEMS based applications must somehow provide memory for RTEMS' code and data space. Although RTEMS' data space must be in RAM, its code space can be located in either ROM or RAM. In addition, the user must allocate RAM for the RTEMS RAM Workspace. The size of this area is application dependent and can be calculated using the formula provided in the Memory Requirements chapter of the Applications Supplement document for a specific target processor. All RTEMS data variables and routine names used by RTEMS begin with the underscore ( _ ) character followed by an upper-case letter. If RTEMS is linked with an application, then the application code should NOT contain any symbols which begin with the underscore character and followed by an upper-case letter to avoid any naming conflicts. All RTEMS directive names should be treated as reserved words. @ifinfo @node Configuring a System Sizing the RTEMS RAM Workspace, Multiprocessing Manager, Configuring a System Determining Memory Requirements, Configuring a System @end ifinfo @section Sizing the RTEMS RAM Workspace The RTEMS RAM Workspace is a user-specified block of memory reserved for use by RTEMS. The application should NOT modify this memory. This area consists primarily of the RTEMS data structures whose exact size depends upon the values specified in the Configuration Table. In addition, task stacks and floating point context areas are dynamically allocated from the RTEMS RAM Workspace. The starting address of the RTEMS RAM Workspace must be aligned on a four-byte boundary. Failure to properly align the workspace area will result in the fatal_error_occurred directive being invoked with the @code{INVALID_ADDRESS} error code. A worksheet is provided in the Memory Requirements chapter of the Applications Supplement document for a specific target processor to assist the user in calculating the minimum size of the RTEMS RAM Workspace for each application. The value calculated with this worksheet is the minimum value that should be specified as the work_space_size parameter of the Configuration Table. The user is cautioned that future versions of RTEMS may not have the same memory requirements per object. Although the value calculated is sufficient for a particular target processor and release of RTEMS, memory usage is subject to change across versions and target processors. The user is advised to allocate somewhat more memory than the worksheet recommends to insure compatibility with future releases for a specific target processor and other target processors. To avoid problems, the user should recalculate the memory requirements each time one of the following events occurs: @itemize @bullet @item a configuration parameter is modified, @item task or interrupt stack requirements change, @item task floating point attribute is altered, @item RTEMS is upgraded, or @item the target processor is changed. @end itemize Failure to provide enough space in the RTEMS RAM Workspace will result in the fatal_error_occurred directive being invoked with the appropriate error code.