Fix support for stepping tick by xExpectedIdleTime (#73)

* Fix support for stepping maximum number of ticks

This commit fixes support for tickless implementations that call
vTaskStepTick() with the maximum number of allowed ticks to step.

vTaskStepTick()
---------------
Function vTaskStepTick() provides a way for the tickless idle
implementation to account for ticks that elapse during tickless idle.
The maximum number of stepped ticks allowed is the number passed to
portSUPPRESS_TICKS_AND_SLEEP().  It is the number of ticks between
xTickCount and xNextTaskUnblockTime.

vTaskStepTick() is specifically intended for use with tickless idle,
so it always executes with the scheduler disabled.  For reference,
compare it with the more general function xTaskCatchUpTicks().

Without this Change
-------------------
Prior to this commit, if a task is supposed to wake at xTickCount ==
0xFFFFFFFF, then when tickless idle ends, function vTaskStepTick()
sets the tick to 0xFFFFFFFF but the task remains on the delayed list
because xTaskIncrementTick() does not execute.  One tick later,
xTaskIncrementTick() executes because it's time to increment xTickCount
to 0x00000000.  An assertion failure occurs in
taskSWITCH_DELAYED_LISTS() because the delayed task list is not
empty.  Other examples of valling vTaskStepTick() with the maximum
allowed number of ticks merely result in a task waking one tick late.

Default Tickless Implementations
--------------------------------
Note that the default tickless implementations never pass the maximum
allowed value to vTaskStepTick().  The default implementations use the
tick interrupt to finish the sleep and allow that one tick to be
counted normally via the tick ISR and xTaskIncrementTick().

* Protect xPendedTicks with critical section

Function xTaskIncrementTick() increments xPendedTicks when the
scheduler is disabled.  That function typically executes inside the tick
ISR.  So code in xTaskCatchUpTicks() must mask interrupts when modifying
xPendedTicks.

* uncrustify tasks.c

* Update tasks.c

Style changes only - added comment and indentation to the two modified files.

* uncrustify

* Add test coverage for new conditional

* Add typecast

Co-authored-by: Cobus van Eeden <35851496+cobusve@users.noreply.github.com>
Co-authored-by: Joseph Julicher <jjulicher@mac.com>
Co-authored-by: RichardBarry <3073890+RichardBarry@users.noreply.github.com>

include/task.h

@@ -3079,7 +3079,7 @@ void vTaskSetTaskNumber( TaskHandle_t xTask,
  * to date with the actual execution time by being skipped forward by a time
  * equal to the idle period.
  */
-void vTaskStepTick( const TickType_t xTicksToJump ) PRIVILEGED_FUNCTION;
+void vTaskStepTick( TickType_t xTicksToJump ) PRIVILEGED_FUNCTION;
 
 /*
  * Only available when configUSE_TICKLESS_IDLE is set to 1.

tasks.c

@@ -2592,12 +2592,34 @@ char * pcTaskGetName( TaskHandle_t xTaskToQuery ) /*lint !e971 Unqualified char
  * 1. */
 #if ( configUSE_TICKLESS_IDLE != 0 )
 
-    void vTaskStepTick( const TickType_t xTicksToJump )
+    void vTaskStepTick( TickType_t xTicksToJump )
     {
         /* Correct the tick count value after a period during which the tick
          * was suppressed.  Note this does *not* call the tick hook function for
          * each stepped tick. */
         configASSERT( ( xTickCount + xTicksToJump ) <= xNextTaskUnblockTime );
+
+        if( ( xTickCount + xTicksToJump ) == xNextTaskUnblockTime )
+        {
+            /* Arrange for xTickCount to reach xNextTaskUnblockTime in
+             * xTaskIncrementTick() when the scheduler resumes.  This ensures
+             * that any delayed tasks are resumed at the correct time. */
+            configASSERT( uxSchedulerSuspended );
+            configASSERT( xTicksToJump != ( TickType_t ) 0 );
+
+            /* Prevent the tick interrupt modifying xPendedTicks simultaneously. */
+            taskENTER_CRITICAL();
+            {
+                xPendedTicks++;
+            }
+            taskEXIT_CRITICAL();
+            xTicksToJump--;
+        }
+        else
+        {
+            mtCOVERAGE_TEST_MARKER();
+        }
+
         xTickCount += xTicksToJump;
         traceINCREASE_TICK_COUNT( xTicksToJump );
     }
@@ -2616,7 +2638,13 @@ BaseType_t xTaskCatchUpTicks( TickType_t xTicksToCatchUp )
     /* Use xPendedTicks to mimic xTicksToCatchUp number of ticks occurring when
      * the scheduler is suspended so the ticks are executed in xTaskResumeAll(). */
     vTaskSuspendAll();
-    xPendedTicks += xTicksToCatchUp;
+
+    /* Prevent the tick interrupt modifying xPendedTicks simultaneously. */
+    taskENTER_CRITICAL();
+    {
+        xPendedTicks += xTicksToCatchUp;
+    }
+    taskEXIT_CRITICAL();
     xYieldOccurred = xTaskResumeAll();
 
     return xYieldOccurred;