Defining a Tasks

Tasks are special procedures the compiler breaks up into individual states.  Like a Sub or Function, a Task can contain basic statements, assembly commands, and local variables. Unlike a Sub or Function, a Task cannot have parameters or return values.

A task is defined with the Task and End Task statement:

Task ADCReader()
End Task

Each time a task is called with the RunTasks statement, an individual states within that task will be executed.  When the end of a state is reached the task will exit passing control back to the calling procedure.  Statements like AllowOthers, WaitWhile, and WaitUntil are used to break the task up into states as follows.

Task ADCReader()
 
  ' state 0 starts here
 
  call SetADCchanel(0)  ' Point ADC to channel 0
 
  TMR0=0: TMR0IF=0      ' Use TMR0 to time the acquisition period for AN0
 
  WaitWhile TMR0IF=0    ' state 0 returns here.
                        ' When this task is called the next time, the
                        ' condition of TMR0IF will be checked.  While it
                        ' remains 0 this state will simply return.
                        ' When the condition goes true the internal state
                        ' pointer for this task will be advanced to the
                        ' next state and then return.
                        ' Internally this statement consumes 1 state
 
  ' state 2 starts here
 
  GO=1                  ' Start the ADC Conversion
 
  WaitUntil GO=0        ' state 2 returns here.
                        ' This is very similar to WaitWhile, except it
                        ' waits until the condition is true.
                        ' Like WaitWhile, this statement consumes 1 state.
 
  ' state 4 starts here
 
  adcValue = ADRES      ' Assign the ADC value to a global variable.
 
 
  ' state 4 ends here
                        ' At the end of a task, the state pointer is set back
                        ' to state 0 before exiting.
End Task

Running Tasks

Before a task is called the state pointers should be initialized with the initTasks() statement.  This will reset the tasks internal state pointer and resume any suspended tasks.  Once tasks have been initialized, they are ready to be called through the RunTasks() statement.

A task will only execute when called using the RunTasks() statement, this usually takes place inside a main execution loop.  The following program will execute the ADCReader task.

Dim adcValue as uInteger ' Used to store the adc reading from the
                         ' ADCReader task
Sub main()
  Call initialize()     ' initialize the hardware here
 
  InitTasks()     ' initialize all tasks
 
  While 1         ' beginning of the task execution loop
    Clrwdt        ' clear the watchdog timer
    RunTasks()    ' Run all tasks 1 cycle
 
    ' Do something with the  dacValue here
 
  End While       ' end of the task execution loop
 
End Sub

Task Related Commands

Following is a brief description of task related commands, for more detail see Appendix A.