Revision as of 16:31, 14 March 2022

OCEOS Task

Introduction

In OCEOS all tasks are defined before scheduling begins and each task assigned a fixed priority, a pre-emption threshold, a current jobs limit, a maximum start to completion time, and an expected minimum inter start request time. A task’s pre-emption threshold limits the tasks that can pre-empt it to those with higher priority than this threshold. Tasks with short run times can use this to avoid context switch overheads. Each task has two main states, enabled or disabled. OCEOS provides system calls to change task state. The state is usually enabled when the task is created, but can be initially disabled. A disabled task will not be executed, and any attempt to start it will be logged and the system state variable updated.
A request to start an enabled task creates an execution instance of the task, a ‘job’. A count is kept for each task of the number of times it has been started, i.e. total number of jobs created. Multiple jobs of the same task can be in existence simultaneously. A limit for the maximum number of these current jobs is set when a task is created, the ‘current jobs limit’. Each task has a current jobs count. This increments each time a task is started and decrements on job completion unless completion creates a further job from this task. A further execution instance of a task is not created if the current jobs count has reached the current jobs limit. Such job creation failures are logged and the system state updated. For each task a record is kept of the shortest time between attempts to create a new job, and a record of the maximum time between these attempts. For each task a record is kept also of the maximum time a job was waiting before starting, the minimum execution time, the maximum execution time, the maximum time from job creation to completion, and the maximum number of job pre-emptions. The system state variable is updated if necessary.
Task chaining is supported. A job can create a new job and pass this to the scheduler or place it on the timed actions queue.
Tasks provide a start address for a termination routine for use if task execution must be abandoned.

Note

All Tasks must be created before oceos_init_finish() is called.

API Functions

API Functions
Directive	Description	main	task	IRQ handler
oceos_task_create()	Create Task	*
oceos_task_start()	Start Task		*	*
oceos_task_timed_start()	Schedule a task to start execution at a given system time		*	*
oceos_task_disable()	Disable Task		*	*
oceos_task_enable()	Enable Task		*	*
oceos_task_self()	Returns the task ID of the currently executing task		*	*
oceos_task_get_priority()	Get priority of a task		*	*
oceos_task_get_status()	Get status of a task		*	*
oceos_task_kill()	Directive to terminate current task		*	*
oceos_task_get_info()	Get task information		*	*

oceos_task_create()

Header File
tasks.h

Description
Create a task. Can only be use before OCEOS starts. Stores the task information in the OCEOS fixed data area. This directive populates the data structures for a task. It should be called after oceos_init() and before oceos_init_finish().
It must be called for each task otherwise oceos_start() will return an error.
Prototype
enum DIRECTIVE_STATUS   oceos_task_create(
    unsigned int taskID,         // unique, 0 to TASKS_MAX_ID
    U32_t priority,              // TASK_MAX_PRIORITY to TASK_MIN_PRIORITY
    U32_t threshold,             // TASK_MAX_PRIORITY to priority
    U32_t jobs_max,              // 1 to JOBS_MAX
    BOOLE_t FP_used,             // whether uses floating point hardware
    BOOLE_t initially_enabled,   // whether task enabled initially
    void (void *) start_function,// task start address
    void (void *) end_function,  // start of task end function
    U32_t time_deadline,         // maximum time to complete (ignore if 0)
    U32_t time_mininterstart     // minimum time between start requests
 );
Parameters

Parameter Description

taskID Unique task ID from 0 to TASKS_MAX_ID

priority TASK_MAX_PRIORITY to TASK_MIN_PRIORITY

threshold TASK_MAX_PRIORITY to priority

jobs_max Number of 1 to JOBS_MAX

FP_used whether uses floating point hardware

initially_enabled whether task enabled initially

start_function task start address

end_function start of task end function

time_deadline maximum time to complete (ignore if 0)

time_mininterstart minimum time between start requests

Returns
This function returns enum DIRECTIVE_STATUS.

enum DIRECTIVE_STATUS Description

INCORRECT_STATE Init Meta Pointer is NULL or
Pointer to Task fixed data is NULL

TOO_MANY Exceeds number of MAX Tasks or
Exceeds number of MAX Jobs

INTERNAL_ERROR System Meta pointer is NULL or
System Meta pointer start sentinel is corrupt

INVALID_ID Failed on task ID check

INVALID_NAME Task ID is already in use

INVALID_PRIORITY Failed on task priority check

INVALID_NUMBER Failed on task threshold check

INVALID_SIZE Failed on task max job check

SUCCESSFUL All is OK

Example Usage
 enum TASK_NAME{
    t_tom,                      // will have task ID 0
    t_dick,                     // will have task ID 1
 };
 extern int task_tom_start(void* data);
 ...
 enum DIRECTIVE_STATUS status;
    // Task 0: priority 10, max jobs 1, enabled (consumer task)
    status  = oceos_task_create(t_tom, // unique, 0 to TASKS_MAX_ID  
	                               10, // TASK_MAX_PRIORITY to TASK_MIN_PRIORITY
								   10, // TASK_MAX_PRIORITY to priority
								    1, // 1 to JOBS_MAX
								    0, // whether uses floating point hardware
				         TASK_ENABLED, // whether task enabled initially
				       task_tom_start, // task start address
						         NULL, // start of task end function
						            0, // maximum time to complete (ignore if 0)
						            0  // minimum time between start requests
				                    );

oceos_task_start()

Header File
tasks.h

Description
Starting a task involves three main stages:

Setting up a job
Finding a free job entry

Setting up this entry

Placing the job on ready queue

Doing a context switch

This function should only be called after OCEOS is initialized and the dynamic task and job structures are set up.
When used from an interrupt handler, the context switch is only done after all nested interrupts have unwound.

Note

FOR SPARC ONLY : Tasks can be started in IRQ routines but CANNOT be started in TRAP handlers.

Prototype
enum DIRECTIVE_STATUS   oceos_task_start(
    const unsigned int taskID, // task ID, must be in range 0 to 254
    void * const ptr           // pointer to data
 );
Parameters

Parameter Description

taskID Task ID must be in range 0 to 254

ptr Pointer to task data

Returns
This function returns enum DIRECTIVE_STATUS.

enum DIRECTIVE_STATUS Description

NOT_CONFIGURED System Meta pointer is NULL or Fixed data start sentinel is corrupt

INCORRECT_STATE One of the System Meta pointers is NULL

INVALID_ID Failed on task ID check

INCORRECT_STATE Tried to start disabled task

TOO_MANY Max number of jobs(requests to start) for task is exceeded

FAILED_TO_PUT_JOB_ON_REDYQ Failed to put job for task on ready Q

SUCCESSFUL All is OK

Example Usage
 enum TASK_NAME{
    t_tom,                      // will have task ID 0
    t_dick,                     // will have task ID 1
 };
 ...
 enum DIRECTIVE_STATUS status;
 status = oceos_task_start(t_tom, NULL); 
 if (SUCCESS != status) {
  // Deal with the problem
  return status;
 }

oceos_task_timed_start()

Header File
tasks.h

Description
Schedule a task to start execution at a given system time.
The before and after offsets define a window around the selected time in which the task may be started.
If the current system time is before the start window a job is created and a corresponding action put on the timed action queue.
If the current system time is within the time window for starting the task, it is started immediately.
If the current system time is after the window, an error is reported.
return_job_id can be stored and used later to cancel if need.
Times are in microseconds.
This function should only be used after oceos_start() is called.

Note

This directive can only be called if timed actions (software timers) are initialized. Please see HERE.

Prototype
enum DIRECTIVE_STATUS oceos_task_timed_start(
    const unsigned int taskID,// Task ID
    void * const ptr,         // data to be used by task
    U64_t start_time,         // system time at which task should start
    U32_t before,             // offset before time in which start o.k.
    U32_t after,              // offset after time in which start o.k.
    U32_t *return_job_id      // in case need to cancel later
);
Parameters

Parameter Description

taskID Task ID must be in range 0 to 254

ptr Pointer to data

start_time System time at which job should start

before Forward tolerance for time

after Backward tolerance for time

return_job_id Return job_id to the user, to remove this job from timed action if needed

Returns
This function returns enum DIRECTIVE_STATUS.

enum DIRECTIVE_STATUS Description

NOT_CONFIGURED System Meta pointer is NULL or
Fixed data start sentinel is corrupt

INCORRECT_STATE One of the System Meta pointers is NULL or
System time is not initialized or Tried to start disabled task

INVALID_ID Failed on task ID check

UNSATISFIED System time is greater when start time plus after time

TOO_MANY Max number of jobs(requests to start) for task is exceeded

INTERNAL_ERROR Failed to put job for task on ready Q

SUCCESSFUL All is OK

Example Usage
enum TASK_NAME{
    t_tom,                      // will have task ID 0
    t_dick,                     // will have task ID 1
};
...
enum DIRECTIVE_STATUS status;
U32_t return_job_id = 0;
U64_t time = oceos_time_sys_get64();
status = oceos_task_timed_start(t_tom, // Task ID must be in range 0 to 254
                                 NULL, // Pointer to data
                       time + 1000000, // System time at which job should start
                                 1000, // Forward tolerance for time
                                 1000, // Backward tolerance for time
                       &return_job_id  // Return job_id to the user, to remove this job from timed action if needed
                                    );
if (SUCCESS != status) {
  // Handle ERROR
  return status;
}

oceos_task_disable()

Header File
tasks.h

Description
Disable a task and remove any current pending jobs on ready queue. A disabled task's jobs will not be put into execution nor put on ready queue.

Note

If execution of a task has already commenced, disabling the task will not prevent it from completing.

Prototype
enum DIRECTIVE_STATUS   oceos_task_disable(
    const unsigned int taskID // task ID, must be in range 0 to 254
 );
Parameters

Parameter Description

taskID Task ID must be in range 0 to 254

Returns
This function returns enum DIRECTIVE_STATUS.

enum DIRECTIVE_STATUS Description

NOT_CONFIGURED System Meta pointer is NULL or
Fixed data start sentinel is corrupt

INTERNAL_ERROR One of the System Meta pointers is NULL or
Dynamic Meta pointer is NULL

INVALID_ID Failed on task ID check

ALREADY_SUSPENDED Task is already disabled

SUCCESSFUL All is OK

Example Usage
 enum TASK_NAME{
    t_tom,                      // will have task ID 0
    t_dick,                     // will have task ID 1
 };
 ...
 enum DIRECTIVE_STATUS status;
 status =  oceos_task_disable(t_tom); 
 if (SUCCESS != status) {
  // Deal with the problem
  return status;
 }

oceos_task_enable()

Header File
tasks.h

Description
Enable a task - only enabled tasks are placed on ready queue or started.

Prototype
enum DIRECTIVE_STATUS   oceos_task_enable(
    const unsigned int taskID  // task ID, must be in range 0 to 254
 );
Parameters

Parameter Description

taskID Task ID must be in range 0 to 254

Returns
This function returns enum DIRECTIVE_STATUS.

enum DIRECTIVE_STATUS Description

NOT_CONFIGURED System Meta pointer is NULL or
Fixed data start sentinel is corrupt

INCORRECT_STATE One of the System Meta pointers is NULL

INTERNAL_ERROR Dynamic Meta pointer is NULL

INVALID_ID Failed on task ID check

ALREADY_SUSPENDED Task is already disabled

SUCCESSFUL All is OK

Example Usage
 enum TASK_NAME{
    t_tom,                      // will have task ID 0
    t_dick,                     // will have task ID 1
 };
 ...
 enum DIRECTIVE_STATUS status;
 status =  oceos_task_enable(t_tom); 
 if (SUCCESS != status) {
  // Deal with the problem
  return status;
 }

oceos_task_self()

Header File
tasks.h

Description
Get the task ID of the current job
Prototype
unsigned int  oceos_task_self();
Parameters

Parameter Description

Returns
This function returns enum DIRECTIVE_STATUS.

unsigned int Description

ID Task ID of currently executing job

TASK_ID_INVALID ERROR

Example Usage
  U32_t id;
  id = oceos_task_self();
  if (TASK_ID_INVALID == id) {
    // Handle ERROR
  }

oceos_task_get_priority()

Header File
tasks.h

Description

Prototype

Parameters

Parameter Description

Returns
This function returns enum DIRECTIVE_STATUS.

enum DIRECTIVE_STATUS Description

INCORRECT_STATE If system Meta pointer is NULL or
Init pointer is NULL or Start up phase check fail or Fixed data checksum failed (check log)

INVALID_NAME If Start Sentinel for fixed area is corrupt or
Start Sentinel for dynamic area is corrupt

INVALID_NUMBER If Configuration and actual parameters do not match
(In configuration file was defined 5 tasks, but created less)

SUCCESSFUL If All OK

Example Usage

oceos_task_get_status()

Header File
tasks.h

Description

Prototype

Parameters

Parameter Description

Returns
This function returns enum DIRECTIVE_STATUS.

enum DIRECTIVE_STATUS Description

INCORRECT_STATE If system Meta pointer is NULL or
Init pointer is NULL or Start up phase check fail or Fixed data checksum failed (check log)

INVALID_NAME If Start Sentinel for fixed area is corrupt or
Start Sentinel for dynamic area is corrupt

INVALID_NUMBER If Configuration and actual parameters do not match
(In configuration file was defined 5 tasks, but created less)

SUCCESSFUL If All OK

Example Usage

oceos_task_kill()

Header File
tasks.h

Description

Prototype

Parameters

Parameter Description

Returns
This function returns enum DIRECTIVE_STATUS.

enum DIRECTIVE_STATUS Description

INCORRECT_STATE If system Meta pointer is NULL or
Init pointer is NULL or Start up phase check fail or Fixed data checksum failed (check log)

INVALID_NAME If Start Sentinel for fixed area is corrupt or
Start Sentinel for dynamic area is corrupt

INVALID_NUMBER If Configuration and actual parameters do not match
(In configuration file was defined 5 tasks, but created less)

SUCCESSFUL If All OK

Example Usage

oceos_task_get_info()

Header File
tasks.h

Description

Prototype

Parameters

Parameter Description

Returns
This function returns enum DIRECTIVE_STATUS.

enum DIRECTIVE_STATUS Description

INCORRECT_STATE If system Meta pointer is NULL or
Init pointer is NULL or Start up phase check fail or Fixed data checksum failed (check log)

INVALID_NAME If Start Sentinel for fixed area is corrupt or
Start Sentinel for dynamic area is corrupt

INVALID_NUMBER If Configuration and actual parameters do not match
(In configuration file was defined 5 tasks, but created less)

SUCCESSFUL If All OK

Example Usage

@@ Line 429: / Line 429: @@
 <span style="color:#1b7ac2">'''Description'''</span><br>
+ Get the task ID of the current job
 <span style="color:#1b7ac2">'''Prototype'''</span><br>
 <syntaxhighlight lang="C">
+unsigned int  oceos_task_self();
 </syntaxhighlight>
 <span style="color:#1b7ac2">'''Parameters'''</span><br>
@@ Line 445: / Line 446: @@
 {| class="wikitable"
 |-
-! enum DIRECTIVE_STATUS !! Description
+! unsigned int !! Description
-|-
-| INCORRECT_STATE || If system Meta pointer is NULL or
-                     Init pointer is NULL or
-                     Start up phase check fail or
-                     Fixed data checksum failed (check log)
-|-
-| INVALID_NAME    || If Start Sentinel for fixed area is corrupt or
-                     Start Sentinel for dynamic area is corrupt
 |-
-| INVALID_NUMBER  || If Configuration and actual parameters do not match
+| ID              || Task ID of currently executing job
-                     (In configuration file was defined 5 tasks, but created less)
 |-
-| SUCCESSFUL     || If All OK
+| TASK_ID_INVALID || ERROR
 |}
 <span style="color:#1b7ac2">'''Example Usage'''</span><br>
 <syntaxhighlight lang="C">
+  U32_t id;
+  id = oceos_task_self();
+  if (TASK_ID_INVALID == id) {
+     // Handle ERROR
+  }
   </syntaxhighlight>
 </blockquote>
 ===<span style="color:#0000ff">oceos_task_get_priority()</span>===
 <blockquote style="border-left-style: none;">

Difference between revisions of "OCEOS/oceos kernel/task"