LUFA Library  120219
Simple Task Scheduler - LUFA/Scheduler/Scheduler.h

Simple round-robbin pseudo-task scheduler. More...

Data Structures

struct  TaskEntry_t
 Scheduler Task List Entry Structure. More...


#define TASK(name)   void name (void)
#define TASK_LIST   TaskEntry_t Scheduler_TaskList[] =
#define TASK_RUN   true
#define TASK_STOP   false


typedef void(* TaskPtr_t )(void)
typedef uint_least16_t SchedulerDelayCounter_t


void Scheduler_Start (void)
void Scheduler_Init (void)
static void Scheduler_ResetDelay (SchedulerDelayCounter_t *const DelayCounter) ATTR_NON_NULL_PTR_ARG(1) ATTR_ALWAYS_INLINE
bool Scheduler_HasDelayElapsed (const uint_least16_t Delay, SchedulerDelayCounter_t *const DelayCounter) ATTR_WARN_UNUSED_RESULT ATTR_NON_NULL_PTR_ARG(2)
void Scheduler_SetTaskMode (const TaskPtr_t Task, const bool TaskStatus)
void Scheduler_SetGroupTaskMode (const uint_least8_t GroupID, const bool TaskStatus)


TaskEntry_t Scheduler_TaskList []
volatile uint_least8_t Scheduler_TotalTasks
volatile SchedulerDelayCounter_t Scheduler_TickCounter

Detailed Description

This module is deprecated and will be removed in a future library release.

Module Source Dependencies

The following files must be built with any user project that uses this module:

Module Description

Simple round-robbin cooperative scheduler for use in basic projects where non real-time tasks need to be executed. Each task is executed in sequence, and can be enabled or disabled individually or as a group.

For a task to yield it must return, thus each task should have persistent data marked with the static keyword.

Each LUFA scheduler task should be written similar to an ISR; it should execute quickly (so that no one task hogs the processor, preventing another from running before some sort of timeout is exceeded). Unlike normal RTOS tasks, each LUFA scheduler task is a regular function, and thus must be designed to be called, and designed to return to the calling scheduler function repeatedly. Data which must be preserved between task calls should be declared as global or (preferably) as a static local variable inside the task.

The scheduler consists of a task list, listing all the tasks which can be executed by the scheduler. Once started, each task is then called one after another, unless the task is stopped by another running task or interrupt.

Usage Example:

      #include <LUFA/Scheduler/Scheduler.h>

      TASK(MyTask1); // Task prototype
      TASK(MyTask2); // Task prototype

          { .Task = MyTask1, .TaskStatus = TASK_RUN, .GroupID = 1  },
          { .Task = MyTask2, .TaskStatus = TASK_RUN, .GroupID = 1  },

      int main(void)

          // Other initialisation here


          // Task implementation here

          // Task implementation here

If desired, the LUFA scheduler does not need to be used in a LUFA powered application. A more conventional approach to application design can be used, or a proper scheduling RTOS inserted in the place of the LUFA scheduler. In the case of the former the USB task must be run manually repeatedly to maintain USB communications, and in the case of the latter a proper RTOS task must be set up to do the same.

Define Documentation

#define TASK (   name)    void name (void)

Creates a new scheduler task body or prototype. Should be used in the form:

      TASK(TaskName); // Prototype

           // Task body

Defines a task list array, containing one or more task entries of the type TaskEntry_t. Each task list should be encased in curly braces and ended with a comma.

Usage Example:

           { .Task = MyTask1, .TaskStatus = TASK_RUN, .GroupID = 1 },
           // More task entries here

Constant, giving the maximum delay in scheduler ticks which can be stored in a variable of type SchedulerDelayCounter_t.

#define TASK_RUN   true

Task status mode constant, for passing to Scheduler_SetTaskMode() or Scheduler_SetGroupTaskMode().

#define TASK_STOP   false

Task status mode constant, for passing to Scheduler_SetTaskMode() or Scheduler_SetGroupTaskMode().

Typedef Documentation

typedef uint_least16_t SchedulerDelayCounter_t

Type define for a variable which can hold a tick delay value for the scheduler up to the maximum delay possible.

typedef void(* TaskPtr_t)(void)

Type define for a pointer to a scheduler task.

Function Documentation

bool Scheduler_HasDelayElapsed ( const uint_least16_t  Delay,
SchedulerDelayCounter_t *const  DelayCounter 

Determines if the given tick delay has elapsed, based on the given delay period and tick counter value.

[in]DelayThe delay to test for, measured in ticks.
[in]DelayCounterThe counter which is storing the starting tick value for the delay.
Boolean true if the delay has elapsed, false otherwise.

Usage Example:

      static SchedulerDelayCounter_t DelayCounter = 10000; // Force immediate run on start-up

      // Task runs every 10000 ticks, 10 seconds for this demo
      if (Scheduler_HasDelayElapsed(10000, &DelayCounter))
           // Code to execute after delay interval elapsed here
void Scheduler_Init ( void  )

Initialises the scheduler so that the scheduler functions can be called before the scheduler itself is started. This must be executed before any scheduler function calls other than Scheduler_Start(), and can be omitted if no such functions could be called before the scheduler is started.

static void Scheduler_ResetDelay ( SchedulerDelayCounter_t *const  DelayCounter) [inline, static]

Resets the delay counter value to the current tick count. This should be called to reset the period for a delay in a task which is dependant on the current tick value.

[out]DelayCounterCounter which is storing the starting tick count for a given delay.
void Scheduler_SetGroupTaskMode ( const uint_least8_t  GroupID,
const bool  TaskStatus 

Sets the task mode for a given task group ID, allowing for an entire group of tasks to have their statuses changed at once.

[in]GroupIDValue of the task group ID whose status is to be changed.
[in]TaskStatusNew task status for tasks in the specified group (TASK_RUN or TASK_STOP).
void Scheduler_SetTaskMode ( const TaskPtr_t  Task,
const bool  TaskStatus 

Sets the task mode for a given task.

[in]TaskName of the task whose status is to be changed.
[in]TaskStatusNew task status for the task (TASK_RUN or TASK_STOP).
void Scheduler_Start ( void  )

Starts the scheduler in its infinite loop, executing running tasks. This should be placed at the end of the user application's main() function, as it can never return to the calling function.

Variable Documentation

Task entry list, containing the scheduler tasks, task statuses and group IDs. Each entry is of type TaskEntry_t and can be manipulated as desired, although it is preferred that the proper Scheduler functions should be used instead of direct manipulation.

Contains the current scheduler tick count, for use with the delay functions. If the delay functions are used in the user code, this should be incremented each tick period so that the delays can be calculated.

volatile uint_least8_t Scheduler_TotalTasks

Contains the total number of tasks in the task list, irrespective of if the task's status is set to TASK_RUN or TASK_STOP.

This value should be treated as read-only, and never altered in user-code.
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