Revision as of 15:24, 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.

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()

oceos_task_start()

oceos_task_timed_start()

oceos_task_disable()

oceos_task_enable()

oceos_task_self()

oceos_task_get_priority()

oceos_task_get_status()

oceos_task_kill()

oceos_task_get_info()

@@ Line 50: / Line 50: @@
 <span style="color:#1b7ac2">'''Description'''</span><br>
+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/oceos kernel/initialisation#oceos_init()|oceos_init()]] and before [[OCEOS/oceos kernel/initialisation#oceos_init_finish()|oceos_init_finish()]].<br>
+It must be called for each task otherwise [[OCEOS/oceos kernel/initialisation#oceos_start()|oceos_start()]] will return an error.
 <span style="color:#1b7ac2">'''Prototype'''</span><br>
 <syntaxhighlight lang="C">
+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
+ );
 </syntaxhighlight>
 <span style="color:#1b7ac2">'''Parameters'''</span><br>
 {| class="wikitable"
 |-
-! Parameter !! Description
+! 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
 |}
 <span style="color:#1b7ac2">'''Returns'''</span><br>

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