Move the call that sets xTimeNow inside the loop that drains the timer queue to ensure higher priority tasks that pre-empt the timer daemon cannot post messages that appear to be in the future to the daemon task.

FreeRTOS/Source/timers.c

@@ -512,10 +512,6 @@ xTIMER *pxTimer;
 portBASE_TYPE xTimerListsWereSwitched, xResult;
 portTickType xTimeNow;
 
-	/* In this case the xTimerListsWereSwitched parameter is not used, but it
-	must be present in the function call. */
-	xTimeNow = prvSampleTimeNow( &xTimerListsWereSwitched );
-
 	while( xQueueReceive( xTimerQueue, &xMessage, tmrNO_DELAY ) != pdFAIL )
 	{
 		pxTimer = xMessage.pxTimer;
@@ -528,6 +524,14 @@ portTickType xTimeNow;
 
 		traceTIMER_COMMAND_RECEIVED( pxTimer, xMessage.xMessageID, xMessage.xMessageValue );
 
+		/* In this case the xTimerListsWereSwitched parameter is not used, but 
+		it must be present in the function call.  prvSampleTimeNow() must be 
+		called after the message is received from xTimerQueue so there is no 
+		possibility of a higher priority task adding a message to the message
+		queue with a time that is ahead of the timer daemon task (because it
+		pre-empted the timer daemon task after the xTimeNow value was set). */
+		xTimeNow = prvSampleTimeNow( &xTimerListsWereSwitched );
+
 		switch( xMessage.xMessageID )
 		{
 			case tmrCOMMAND_START :
@@ -680,3 +684,6 @@ xTIMER *pxTimer = ( xTIMER * ) xTimer;
 to include software timer functionality.  If you want to include software timer
 functionality then ensure configUSE_TIMERS is set to 1 in FreeRTOSConfig.h. */
 #endif /* configUSE_TIMERS == 1 */
+
+
+