RTEMS 4.7.1 On-Line Library

Configuring a System User Extensions Table

RTEMS Ada User's Guide

22.9: 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 Ada record:

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;

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.
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.
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.
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.
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.
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.
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.
fatal: is the address of the user-supplied subroutine for the FATAL extension. This RTEMS extension of fatal error handling is called from the rtems.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.

A typical declaration for a User Extension Table which defines the TASK_CREATE, TASK_DELETE, TASK_SWITCH, and FATAL extension might appear as follows:

User_Extensions : RTEMS.Extensions_Table := ( Task_Create_Extension'Access, null, null, Task_Delete_Extension'Access, Task_Switch_Extension'Access, null, null, Fatal_Extension'Access );

More information regarding the user extensions is provided in the User Extensions chapter.

RTEMS Ada User's Guide