Difference between revisions of "OCEOS/oceos kernel/task"
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=<span style="color:#0000ff">'''OCEOS Task'''</span>= | =<span style="color:#0000ff">'''OCEOS Task'''</span>= | ||
==<span style="color:#0000ff">Introduction</span>== | ==<span style="color:#0000ff">Introduction</span>== | ||
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.<br> | |||
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.<br> | |||
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.<br> | |||
Tasks provide a start address for a termination routine for use if task execution must be abandoned. | |||
<blockquote style="background-color: #c6e2f7; border-left-style: solid; border-left-width: 3px; border-left-color: blue; "> '''Note'''<br> | |||
All Tasks must be created before [[OCEOS/oceos kernel/initialisation#oceos_init_finish()|oceos_init_finish()]] is called. | |||
</blockquote> | |||
==<span style="color:#0000ff">API Functions</span>== | ==<span style="color:#0000ff">API Functions</span>== | ||
Revision as of 12:48, 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
| Directive | Description | main | task | IRQ handler |
|---|---|---|---|---|
| oceos_init() | Initialize fixed data | * |