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Task scheduler library
1.0
Arduino library for simply executing tasks in parallel
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Library providing a simple task scheduler for multitasking. More...
#include <Arduino.h>
Go to the source code of this file.
Macros | |
#define | MAX_TASK_CNT 8 |
Maximum number of parallel tasks. | |
Typedefs | |
typedef void(* | Task) (void) |
Example prototype for a function than can be executed as a task. | |
Functions | |
void | Tasks_Init (void) |
Initialize and reset the tasks library. More... | |
bool | Tasks_Add (Task func, int16_t period, int16_t delay=0) |
Add a task to the task scheduler. More... | |
bool | Tasks_Remove (Task func) |
Remove a task from the task scheduler. More... | |
bool | Tasks_Delay (Task func, int16_t delay) |
Delay execution of a task. More... | |
bool | Tasks_SetState (Task func, bool state) |
Enable or disable the execution of a task. More... | |
bool | Tasks_Start_Task (Task func) |
Activate a task in the scheduler. More... | |
bool | Tasks_Pause_Task (Task func) |
Deactivate a task in the scheduler. More... | |
void | Tasks_Start (void) |
Start the task scheduler. More... | |
void | Tasks_Pause (void) |
Pause the task scheduler. More... | |
Library providing a simple task scheduler for multitasking.
This library implements a very basic scheduler that is executed in parallel to the 1ms timer interrupt used for the millis() function. It enables users to define cyclic tasks or tasks that should be executed in the future in parallel to the normal program execution inside the main loop.
The task scheduler is executed every 1ms.
The currently running task is always interrupted by this and only continued to be executed after all succeeding tasks have finished. This means that always the task started last has the highest priority. This effect needs to be kept in mind when programming a software using this library.
Deadlocks can appear when one task waits for another taks which was started before. Additionally it is likely that timing critical tasks will not execute properly when they are interrupted for too long by other tasks. Thus it is recommended to keep the tasks as small and fast as possible.
The Arduino ATMega (8-bit AVR) leaves the interrupts state shortly after starting the task scheduler which makes the scheduler reentrant and allows any other interrupt (timer, UART, etc.) to be triggered. The Arduino SAM (32-bit ARM) enables other interrupts by using the lowest possible priority (15) for the task scheduler interrupt.
Warning The Arduino SAM does not support reeantrant interrupts due to HW limitations. This means that unlike the Arduino ATMega the DUE is not able to execute fast 1ms tasks several times before finishing a slower tasks with for example a 10ms timebase. This problem will be especially visible if the sum of the execution time of all tasks is greater than the execution period of the fastest task.
Definition in file Tasks.h.
bool Tasks_Add | ( | Task | func, |
int16_t | period, | ||
int16_t | delay = 0 |
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) |
Add a task to the task scheduler.
A new task is added to the scheduler with a given execution period and delay until first execution.
If no delay is given the task is executed at once or after starting the task scheduler (see Tasks_Start())
If a period of 0ms is given, the task is executed only once and then removed automatically.
To avoid ambiguities, a function can only be added once to the scheduler. Trying to add it a second time will reset and overwrite the settings of the existing task.
Used HW blocks:
- Arduino ATMega: TIMER0_COMPA_vect
- Arduino SAM: TC3
[in] | func | Function to be executed. The function prototype should be similar to this: "void userFunction(void)" |
[in] | period | Execution period of the task in ms (0 to 32767) |
[in] | delay | Delay until first execution of task in ms (0 to 32767) |
MAX_TASK_CNT
in file Tasks.h
bool Tasks_Delay | ( | Task | func, |
int16_t | delay | ||
) |
Delay execution of a task.
The task is delayed starting from the last 1ms timer tick which means the delay time is accurate to -1ms to 0ms.
This overwrites any previously set delay setting for this task and thus even allows earlier execution of a task. Delaying the task by <2ms forces it to be executed during the next 1ms timer tick. This means that the task might be called at any time anyway in case it was added multiple times to the task scheduler.
Used HW blocks:
- Arduino ATMega: TIMER0_COMPA_vect
- Arduino SAM: TC3
[in] | func | Function that should be delayed |
[in] | delay | Delay in ms (0 to 32767) |
void Tasks_Init | ( | void | ) |
void Tasks_Pause | ( | void | ) |
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inline |
Deactivate a task in the scheduler.
Pause execution of the specified task. Possible parallel tasks are not affected. This is a simple inlined function setting the 'state' argument for Tasks_SetState().
Used HW blocks:
- Arduino ATMega: TIMER0_COMPA_vect
- Arduino SAM: TC3
[in] | func | Function to be paused |
bool Tasks_Remove | ( | Task | func | ) |
Remove a task from the task scheduler.
Remove the specified task from the scheduler and free the slot again.
Used HW blocks:
- Arduino ATMega: TIMER0_COMPA_vect
- Arduino SAM: TC3
[in] | func | Function name that should be removed. |
bool Tasks_SetState | ( | Task | func, |
bool | state | ||
) |
Enable or disable the execution of a task.
Temporary pause or resume function for execution of single tasks by scheduler. This will not stop the task in case it is currently being executed but just prevents the task from being executed again in case its state is set to 'false' (inactive).
Used HW blocks:
- Arduino ATMega: TIMER0_COMPA_vect
- Arduino SAM: TC3
[in] | func | Function to be paused/resumed. The function prototype should be similar to this: "void userFunction(void)" |
[in] | state | New function state (false=pause, true=resume) |
void Tasks_Start | ( | void | ) |
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inline |
Activate a task in the scheduler.
Resume execution of the specified task. Possible parallel tasks are not affected. This is a simple inlined function setting the 'state' argument for Tasks_SetState().
Used HW blocks:
- Arduino ATMega: TIMER0_COMPA_vect
- Arduino SAM: TC3
[in] | func | Function to be activated |