OCEOS/oceos kernel/task
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
| 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 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 if available
- setting up this entry including passing it the data void *
- placing the job on readyQ
- doing a context switch
This function should only be called after OCEOS is initialized and the dynamic task and job structures set up
When used from an interrupt handler, the context switch is only done after all nested interrupts have unwound.
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_timed_start()
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_disable()
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_enable()
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_self()
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_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