Add affinity to IDLE tasks in SMP systems (#1415)

examples/template_configuration/FreeRTOSConfig.h

diff --git a/examples/template_configuration/FreeRTOSConfig.h b/examples/template_configuration/FreeRTOSConfig.h
index 7859a5c..b8c0e7f 100644
--- a/examples/template_configuration/FreeRTOSConfig.h
+++ b/examples/template_configuration/FreeRTOSConfig.h
@@ -558,6 +558,13 @@
  * tskNO_AFFINITY if left undefined. */
 #define configTIMER_SERVICE_TASK_CORE_AFFINITY    tskNO_AFFINITY
 
+/* When using SMP (i.e. configNUMBER_OF_CORES is greater than one), set
+ * configIDLE_AFFINITY to 1 to pin each Idle task to its corresponding
+ * core. When set to 1, Idle task N will only run on core N, using an affinity
+ * mask of (1 << N).  Set to 0 to allow the scheduler to run Idle tasks on any
+ * available core.  Defaults to 0 if left undefined. */
+#define configIDLE_AFFINITY                       0
+
 /******************************************************************************/
 /* ARMv8-M secure side port related definitions. ******************************/
 /******************************************************************************/

include/FreeRTOS.h

diff --git a/include/FreeRTOS.h b/include/FreeRTOS.h
index 63e2feb..83fd430 100644
--- a/include/FreeRTOS.h
+++ b/include/FreeRTOS.h
@@ -377,6 +377,10 @@
     #define configIDLE_SHOULD_YIELD    1
 #endif
 
+#ifndef configIDLE_AFFINITY
+    #define configIDLE_AFFINITY    0
+#endif
+
 #if configMAX_TASK_NAME_LEN < 1
     #error configMAX_TASK_NAME_LEN must be set to a minimum of 1 in FreeRTOSConfig.h
 #endif

tasks.c

diff --git a/tasks.c b/tasks.c
index c596c47..2523515 100644
--- a/tasks.c
+++ b/tasks.c
@@ -3687,8 +3687,13 @@
                 /* Assign idle task to each core before SMP scheduler is running. */
                 xIdleTaskHandles[ xCoreID ]->xTaskRunState = xCoreID;
                 pxCurrentTCBs[ xCoreID ] = xIdleTaskHandles[ xCoreID ];
+                #if ( ( configIDLE_AFFINITY == 1 ) && ( configUSE_CORE_AFFINITY == 1 ) )
+                {
+                    xIdleTaskHandles[ xCoreID ]->uxCoreAffinityMask = ( ( UBaseType_t ) 1U << ( UBaseType_t ) xCoreID );
+                }
+                #endif
             }
-            #endif
+            #endif /* if ( configNUMBER_OF_CORES == 1 ) */
         }
     }