@c @c COPYRIGHT (c) 1988-1999. @c On-Line Applications Research Corporation (OAR). @c All rights reserved. @c @c $Id$ @c @chapter Timer Manager @cindex timers @section Introduction The timer manager provides support for timer facilities. The directives provided by the timer manager are: @itemize @bullet @item @code{@value{DIRPREFIX}timer_create} - Create a timer @item @code{@value{DIRPREFIX}timer_ident} - Get ID of a timer @item @code{@value{DIRPREFIX}timer_cancel} - Cancel a timer @item @code{@value{DIRPREFIX}timer_delete} - Delete a timer @item @code{@value{DIRPREFIX}timer_fire_after} - Fire timer after interval @item @code{@value{DIRPREFIX}timer_fire_when} - Fire timer when specified @item @code{@value{DIRPREFIX}timer_reset} - Reset an interval timer @end itemize @section Background @subsection Required Support A clock tick is required to support the functionality provided by this manager. @subsection Timers A timer is an RTEMS object which allows the application to schedule operations to occur at specific times in the future. User supplied timer service routines are invoked by the @code{@value{DIRPREFIX}clock_tick} directive when the timer fires. Timer service routines may perform any operations or directives which normally would be performed by the application code which invoked the @code{@value{DIRPREFIX}clock_tick} directive. The timer can be used to implement watchdog routines which only fire to denote that an application error has occurred. The timer is reset at specific points in the application to insure that the watchdog does not fire. Thus, if the application does not reset the watchdog timer, then the timer service routine will fire to indicate that the application has failed to reach a reset point. This use of a timer is sometimes referred to as a "keep alive" or a "deadman" timer. @subsection Timer Service Routines The timer service routine should adhere to @value{LANGUAGE} calling conventions and have a prototype similar to the following: @ifset is-C @findex rtems_timer_service_routine @example rtems_timer_service_routine user_routine( rtems_id timer_id, void *user_data ); @end example @end ifset @ifset is-Ada @example procedure User_Routine( Timer_ID : in RTEMS.ID; User_Data : in System.Address ); @end example @end ifset Where the timer_id parameter is the RTEMS object ID of the timer which is being fired and user_data is a pointer to user-defined information which may be utilized by the timer service routine. The argument user_data may be NULL. @section Operations @subsection Creating a Timer The @code{@value{DIRPREFIX}timer_create} directive creates a timer by allocating a Timer Control Block (TMCB), assigning the timer a user-specified name, and assigning it a timer ID. Newly created timers do not have a timer service routine associated with them and are not active. @subsection Obtaining Timer IDs When a timer is created, RTEMS generates a unique timer ID and assigns it to the created timer until it is deleted. The timer ID may be obtained by either of two methods. First, as the result of an invocation of the @code{@value{DIRPREFIX}timer_create} directive, the timer ID is stored in a user provided location. Second, the timer ID may be obtained later using the @code{@value{DIRPREFIX}timer_ident} directive. The timer ID is used by other directives to manipulate this timer. @subsection Initiating an Interval Timer The @code{@value{DIRPREFIX}timer_fire_after} directive initiates a timer to fire a user provided timer service routine after the specified number of clock ticks have elapsed. When the interval has elapsed, the timer service routine will be invoked from the @code{@value{DIRPREFIX}clock_tick} directive. @subsection Initiating a Time of Day Timer The @code{@value{DIRPREFIX}timer_fire_when} directive initiates a timer to fire a user provided timer service routine when the specified time of day has been reached. When the interval has elapsed, the timer service routine will be invoked from the @code{@value{DIRPREFIX}clock_tick} directive. @subsection Canceling a Timer The @code{@value{DIRPREFIX}timer_cancel} directive is used to halt the specified timer. Once canceled, the timer service routine will not fire unless the timer is reinitiated. The timer can be reinitiated using the @code{@value{DIRPREFIX}timer_reset}, @code{@value{DIRPREFIX}timer_fire_after}, and @code{@value{DIRPREFIX}timer_fire_when} directives. @subsection Resetting a Timer The @code{@value{DIRPREFIX}timer_reset} directive is used to restore an interval timer initiated by a previous invocation of @code{@value{DIRPREFIX}timer_fire_after} to its original interval length. If the timer has not been used or the last usage of this timer was by a @code{@value{DIRPREFIX}timer_fire_when} directive, then an error is returned. The timer service routine is not changed or fired by this directive. @subsection Deleting a Timer The @code{@value{DIRPREFIX}timer_delete} directive is used to delete a timer. If the timer is running and has not expired, the timer is automatically canceled. The timer's control block is returned to the TMCB free list when it is deleted. A timer can be deleted by a task other than the task which created the timer. Any subsequent references to the timer's name and ID are invalid. @section Directives This section details the timer manager's directives. A subsection is dedicated to each of this manager's directives and describes the calling sequence, related constants, usage, and status codes. @c @c @c @page @subsection TIMER_CREATE - Create a timer @cindex create a timer @subheading CALLING SEQUENCE: @ifset is-C @findex rtems_timer_create @example rtems_status_code rtems_timer_create( rtems_name name, rtems_id *id ); @end example @end ifset @ifset is-Ada @example procedure Timer_Create ( Name : in RTEMS.Name; ID : out RTEMS.ID; Result : out RTEMS.Status_Codes ); @end example @end ifset @subheading DIRECTIVE STATUS CODES: @code{@value{RPREFIX}SUCCESSFUL} - timer created successfully@* @code{@value{RPREFIX}INVALID_NAME} - invalid timer name@* @code{@value{RPREFIX}TOO_MANY} - too many timers created @subheading DESCRIPTION: This directive creates a timer. The assigned timer id is returned in id. This id is used to access the timer with other timer manager directives. For control and maintenance of the timer, RTEMS allocates a TMCB from the local TMCB free pool and initializes it. @subheading NOTES: This directive will not cause the calling task to be preempted. @c @c @c @page @subsection TIMER_IDENT - Get ID of a timer @cindex obtain the ID of a timer @subheading CALLING SEQUENCE: @ifset is-C @findex rtems_timer_ident @example rtems_status_code rtems_timer_ident( rtems_name name, rtems_id *id ); @end example @end ifset @ifset is-Ada @example procedure Timer_Ident ( Name : in RTEMS.Name; ID : out RTEMS.ID; Result : out RTEMS.Status_Codes ); @end example @end ifset @subheading DIRECTIVE STATUS CODES: @code{@value{RPREFIX}SUCCESSFUL} - timer identified successfully@* @code{@value{RPREFIX}INVALID_NAME} - timer name not found @subheading DESCRIPTION: This directive obtains the timer id associated with the timer name to be acquired. If the timer name is not unique, then the timer id will match one of the timers with that name. However, this timer id is not guaranteed to correspond to the desired timer. The timer id is used to access this timer in other timer related directives. @subheading NOTES: This directive will not cause the running task to be preempted. @c @c @c @page @subsection TIMER_CANCEL - Cancel a timer @cindex cancel a timer @subheading CALLING SEQUENCE: @ifset is-C @findex rtems_timer_cancel @example rtems_status_code rtems_timer_cancel( rtems_id id ); @end example @end ifset @ifset is-Ada @example procedure Timer_Cancel ( ID : in RTEMS.ID; Result : out RTEMS.Status_Codes ); @end example @end ifset @subheading DIRECTIVE STATUS CODES: @code{@value{RPREFIX}SUCCESSFUL} - timer canceled successfully@* @code{@value{RPREFIX}INVALID_ID} - invalid timer id @subheading DESCRIPTION: This directive cancels the timer id. This timer will be reinitiated by the next invocation of @code{@value{DIRPREFIX}timer_reset}, @code{@value{DIRPREFIX}timer_fire_after}, or @code{@value{DIRPREFIX}timer_fire_when} with id. @subheading NOTES: This directive will not cause the running task to be preempted. @c @c @c @page @subsection TIMER_DELETE - Delete a timer @cindex delete a timer @subheading CALLING SEQUENCE: @ifset is-C @findex rtems_timer_delete @example rtems_status_code rtems_timer_delete( rtems_id id ); @end example @end ifset @ifset is-Ada @example procedure Timer_Delete ( ID : in RTEMS.ID; Result : out RTEMS.Status_Codes ); @end example @end ifset @subheading DIRECTIVE STATUS CODES: @code{@value{RPREFIX}SUCCESSFUL} - timer deleted successfully@* @code{@value{RPREFIX}INVALID_ID} - invalid timer id @subheading DESCRIPTION: This directive deletes the timer specified by id. If the timer is running, it is automatically canceled. The TMCB for the deleted timer is reclaimed by RTEMS. @subheading NOTES: This directive will not cause the running task to be preempted. A timer can be deleted by a task other than the task which created the timer. @c @c @c @page @subsection TIMER_FIRE_AFTER - Fire timer after interval @cindex fire a timer after an interval @subheading CALLING SEQUENCE: @ifset is-C @findex rtems_timer_fire_after @example rtems_status_code rtems_timer_fire_after( rtems_id id, rtems_interval ticks, rtems_timer_service_routine_entry routine, void *user_data ); @end example @end ifset @ifset is-Ada @example procedure Timer_Fire_After ( ID : in RTEMS.ID; Ticks : in RTEMS.Interval; Routine : in RTEMS.Timer_Service_Routine; User_Data : in RTEMS.Address; Result : out RTEMS.Status_Codes ); @end example @end ifset @subheading DIRECTIVE STATUS CODES: @code{@value{RPREFIX}SUCCESSFUL} - timer initiated successfully@* @code{@value{RPREFIX}INVALID_ID} - invalid timer id@* @code{@value{RPREFIX}INVALID_NUMBER} - invalid interval @subheading DESCRIPTION: This directive initiates the timer specified by id. If the timer is running, it is automatically canceled before being initiated. The timer is scheduled to fire after an interval ticks clock ticks has passed. When the timer fires, the timer service routine routine will be invoked with the argument user_data. @subheading NOTES: This directive will not cause the running task to be preempted. @c @c @c @page @subsection TIMER_FIRE_WHEN - Fire timer when specified @cindex fire a timer at wall time @subheading CALLING SEQUENCE: @ifset is-C @findex rtems_timer_fire_when @example rtems_status_code rtems_timer_fire_when( rtems_id id, rtems_time_of_day *wall_time, rtems_timer_service_routine_entry routine, void *user_data ); @end example @end ifset @ifset is-Ada @example procedure Timer_Fire_When ( ID : in RTEMS.ID; Wall_Time : in RTEMS.Time_Of_Day; Routine : in RTEMS.Timer_Service_Routine; User_Data : in RTEMS.Address; Result : out RTEMS.Status_Codes ); @end example @end ifset @subheading DIRECTIVE STATUS CODES: @code{@value{RPREFIX}SUCCESSFUL} - timer initiated successfully@* @code{@value{RPREFIX}INVALID_ID} - invalid timer id@* @code{@value{RPREFIX}NOT_DEFINED} - system date and time is not set@* @code{@value{RPREFIX}INVALID_CLOCK} - invalid time of day @subheading DESCRIPTION: This directive initiates the timer specified by id. If the timer is running, it is automatically canceled before being initiated. The timer is scheduled to fire at the time of day specified by wall_time. When the timer fires, the timer service routine routine will be invoked with the argument user_data. @subheading NOTES: This directive will not cause the running task to be preempted. @c @c @c @page @subsection TIMER_RESET - Reset an interval timer @cindex reset a timer @subheading CALLING SEQUENCE: @ifset is-C @findex rtems_timer_reset @example rtems_status_code rtems_timer_reset( rtems_id id ); @end example @end ifset @ifset is-Ada @example procedure Timer_Reset ( ID : in RTEMS.ID; Result : out RTEMS.Status_Codes ); @end example @end ifset @subheading DIRECTIVE STATUS CODES: @code{@value{RPREFIX}SUCCESSFUL} - timer reset successfully@* @code{@value{RPREFIX}INVALID_ID} - invalid timer id@* @code{@value{RPREFIX}NOT_DEFINED} - attempted to reset a when or newly created timer @subheading DESCRIPTION: This directive resets the timer associated with id. This timer must have been previously initiated with a @code{@value{DIRPREFIX}timer_fire_after} directive. If active the timer is canceled, after which the timer is reinitiated using the same interval and timer service routine which the original @code{@value{DIRPREFIX}timer_fire_after} directive used. @subheading NOTES: If the timer has not been used or the last usage of this timer was by a @code{@value{DIRPREFIX}timer_fire_when} directive, then the @code{@value{RPREFIX}NOT_DEFINED} error is returned. Restarting a cancelled after timer results in the timer being reinitiated with its previous timer service routine and interval. This directive will not cause the running task to be preempted.