IPC@CHIP Documentation - SC12 @CHIP-RTOS V1.10

Figure 1 ) Sleep Based Periodic Loop
The SLEEP_10HZ constant used in this example is adjusted based on the expected system loading,
including CPU dwell within the Activity_10Hz procedure. This would require some timing
measurements to be made during the program's development.
Precisely Periodic
A precisely periodic loop can be controlled with an RTOS timer. This will result in a periodic loop
which on average tracks the CPU quartz clock. A RTOS timer periodically wakes up the periodic task
loop as illustrated below in Figure 2.
static int TaskID_10Hz ;
void huge Task_10Hz(void)
{
while (1) // 10 Hz loop
{
RTX_Sleep_Request () ;
Activity_10Hz() ; // Get here each 100 ms.
}
}
static void huge Timer_Callback(void) // Clean 10 Hz
{
RTX_Wakeup (TaskID_10Hz) ;
}
static TimerID ;
static TimerProc_Structure Timer_Spec = {
&TimerID,
Timer_Callback,
0,
{ '1', '0', 'H', 'z'},
100 // .interval = 100 milliseconds
} ;
void Initialize(void)
{
extern TaskDefBlock Task_10Hz_Def ;
RTX_Create_Task (&TaskID_10Hz, &Task_10Hz_Def) ;
RTX_Install_Timer (&Timer_Spec) ;
RTX_Start_Timer (TimerID) ;
}
Figure 2 ) Timer Based Periodic Loop
An alternative method here would be to use RTX_Suspend_Task in Task_10Hz and
RTX_Resume_Task in Timer_Callback. However, the RTX_Wakeup has the advantage of a wakeup
pending flag used in the implementation which covers for the case where, due to CPU loading, the
Task_10Hz may not yet have reached the RTX_Sleep_Request call before the RTX_Wakeup is
executed in the Timer_Callback. In this case when the RTX_Sleep_Request is later called in
Task_10Hz, the API will return immediately after clearing the task's internal wakeup pending flag,
which had been set when Timer_Callback called RTX_Wakeup before Task_10Hz reached its sleep.
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