New API xTaskPeriodicDelay (#1349)

include/FreeRTOS.h

@@ -1770,6 +1770,14 @@
     #define traceRETURN_vTaskDelete()
 #endif
 
+#ifndef traceENTER_xTaskPeriodicDelay
+    #define traceENTER_xTaskPeriodicDelay( pxPreviousWakeTime, xTimeIncrement )
+#endif
+
+#ifndef traceRETURN_xTaskPeriodicDelay
+    #define traceRETURN_xTaskPeriodicDelay( xIncrements )
+#endif
+
 #ifndef traceENTER_xTaskDelayUntil
     #define traceENTER_xTaskDelayUntil( pxPreviousWakeTime, xTimeIncrement )
 #endif

include/task.h

@@ -893,6 +893,43 @@ void vTaskDelete( TaskHandle_t xTaskToDelete ) PRIVILEGED_FUNCTION;
  */
 void vTaskDelay( const TickType_t xTicksToDelay ) PRIVILEGED_FUNCTION;
 
+/**
+ * task. h
+ * @code{c}
+ * TickType_t xTaskPeriodicDelay( TickType_t *pxPreviousWakeTime, const TickType_t xTimeIncrement );
+ * @endcode
+ *
+ * INCLUDE_xTaskDelayUntil must be defined as 1 for this function to be available.
+ * See the configuration section for more information.
+ *
+ * Periodic task delay to ensure a constant execution frequency.
+ *
+ * This function is similar to xTaskDelayUntil () with a few important differences:
+ * - pxPreviousWakeTime contains the last past wake time, so it never runs away
+ * - if you suspend the task, when you resume it pxPreviousWakeTime will instantly
+ *   catch up all skipped increments
+ * - it returns the number of increments added to pxPreviosWakeTime
+ *
+ * @param pxPreviousWakeTime Pointer to a variable that holds the time at which the
+ * task was last unblocked.  The variable must be initialised with the current time
+ * prior to its first use.  Following this the variable is automatically updated.
+ *
+ * @param xTimeIncrement The cycle time period.  The task will be unblocked at
+ * time *pxPreviousWakeTime + xTimeIncrement.  Passing the same xTimeIncrement
+ * parameter value will cause the task to execute with a fixed interval.
+ *
+ * @return Number of times xTimeIncrement has been added to pxPreviousWakeTime.
+ * It is 0 on the first call or if not enough ticks have been elapsed since the
+ * last call, 1 in normal circumstances or more than 1 if some period has been
+ * skipped for some reason (e.g. when the caller task is suspended for more than
+ * xTimeIncrement ticks).
+ *
+ * \defgroup xTaskPeriodicDelay xTaskPeriodicDelay
+ * \ingroup TaskCtrl
+ */
+TickType_t xTaskPeriodicDelay( TickType_t * const pxPreviousWakeTime,
+                               const TickType_t xTimeIncrement ) PRIVILEGED_FUNCTION;
+
 /**
  * task. h
  * @code{c}

tasks.c

@@ -2362,6 +2362,55 @@
 
 #if ( INCLUDE_xTaskDelayUntil == 1 )
 
+    TickType_t xTaskPeriodicDelay( TickType_t * const pxPreviousWakeTime,
+                                   const TickType_t xTimeIncrement )
+    {
+        TickType_t xIncrements, xTicksIncrements, xTicksToWait;
+
+        traceENTER_xTaskPeriodicDelay( pxPreviousWakeTime, xTimeIncrement );
+
+        configASSERT( pxPreviousWakeTime );
+        configASSERT( ( xTimeIncrement > 0U ) );
+
+        vTaskSuspendAll();
+        {
+            /* As long as everything is the same type, this plays well with overflows */
+            const TickType_t xTicksElapsed = xTickCount - *pxPreviousWakeTime;
+
+            configASSERT( uxSchedulerSuspended == 1U );
+
+            /* Number of increments to catch up: it could be 0 if
+             * not enough ticks have elapsed, 1 in the common case or
+             * more than 1 if the task has not been resumed in time */
+            xIncrements = xTicksElapsed / xTimeIncrement;
+            xTicksIncrements = xIncrements * xTimeIncrement;
+
+            /* Update to the last wake time */
+            *pxPreviousWakeTime += xTicksIncrements;
+
+            /* Ticks to the next wake time */
+            xTicksToWait = xTimeIncrement - ( xTicksElapsed - xTicksIncrements );
+
+            prvAddCurrentTaskToDelayedList( xTicksToWait, pdFALSE );
+        }
+
+        /* Force a reschedule if xTaskResumeAll has not already done so, we may
+         * have put ourselves to sleep. */
+        if( xTaskResumeAll() == pdFALSE )
+        {
+            taskYIELD_WITHIN_API();
+        }
+        else
+        {
+            mtCOVERAGE_TEST_MARKER();
+        }
+
+        traceRETURN_xTaskPeriodicDelay( xIncrements );
+
+        return xIncrements;
+    }
+
+
     BaseType_t xTaskDelayUntil( TickType_t * const pxPreviousWakeTime,
                                 const TickType_t xTimeIncrement )
     {