]> git.sur5r.net Git - freertos/blobdiff - FreeRTOS/Source/portable/GCC/ARM_CM4F/port.c
Update version number to V8.0.0 (without the release candidate number).
[freertos] / FreeRTOS / Source / portable / GCC / ARM_CM4F / port.c
index 7051e8d3b1a058908502a43046b2a12866498bc8..3a4bb684a746c91aaca2e6044082210531c3d97b 100644 (file)
@@ -1,5 +1,6 @@
 /*\r
-    FreeRTOS V7.5.0 - Copyright (C) 2013 Real Time Engineers Ltd.\r
+    FreeRTOS V8.0.0 - Copyright (C) 2014 Real Time Engineers Ltd.\r
+    All rights reserved\r
 \r
     VISIT http://www.FreeRTOS.org TO ENSURE YOU ARE USING THE LATEST VERSION.\r
 \r
 \r
 #ifndef configSYSTICK_CLOCK_HZ\r
        #define configSYSTICK_CLOCK_HZ configCPU_CLOCK_HZ\r
+       /* Ensure the SysTick is clocked at the same frequency as the core. */\r
+       #define portNVIC_SYSTICK_CLK_BIT        ( 1UL << 2UL )\r
+#else\r
+       /* The way the SysTick is clocked is not modified in case it is not the same\r
+       as the core. */\r
+       #define portNVIC_SYSTICK_CLK_BIT        ( 0 )\r
 #endif\r
 \r
 /* Constants required to manipulate the core.  Registers first... */\r
-#define portNVIC_SYSTICK_CTRL_REG                      ( * ( ( volatile unsigned long * ) 0xe000e010 ) )\r
-#define portNVIC_SYSTICK_LOAD_REG                      ( * ( ( volatile unsigned long * ) 0xe000e014 ) )\r
-#define portNVIC_SYSTICK_CURRENT_VALUE_REG     ( * ( ( volatile unsigned long * ) 0xe000e018 ) )\r
-#define portNVIC_SYSPRI2_REG                           ( * ( ( volatile unsigned long * ) 0xe000ed20 ) )\r
+#define portNVIC_SYSTICK_CTRL_REG                      ( * ( ( volatile uint32_t * ) 0xe000e010 ) )\r
+#define portNVIC_SYSTICK_LOAD_REG                      ( * ( ( volatile uint32_t * ) 0xe000e014 ) )\r
+#define portNVIC_SYSTICK_CURRENT_VALUE_REG     ( * ( ( volatile uint32_t * ) 0xe000e018 ) )\r
+#define portNVIC_SYSPRI2_REG                           ( * ( ( volatile uint32_t * ) 0xe000ed20 ) )\r
 /* ...then bits in the registers. */\r
-#define portNVIC_SYSTICK_CLK_BIT                       ( 1UL << 2UL )\r
 #define portNVIC_SYSTICK_INT_BIT                       ( 1UL << 1UL )\r
 #define portNVIC_SYSTICK_ENABLE_BIT                    ( 1UL << 0UL )\r
 #define portNVIC_SYSTICK_COUNT_FLAG_BIT                ( 1UL << 16UL )\r
 #define portNVIC_PENDSVCLEAR_BIT                       ( 1UL << 27UL )\r
 #define portNVIC_PEND_SYSTICK_CLEAR_BIT                ( 1UL << 25UL )\r
 \r
-#define portNVIC_PENDSV_PRI                                    ( ( ( unsigned long ) configKERNEL_INTERRUPT_PRIORITY ) << 16UL )\r
-#define portNVIC_SYSTICK_PRI                           ( ( ( unsigned long ) configKERNEL_INTERRUPT_PRIORITY ) << 24UL )\r
+#define portNVIC_PENDSV_PRI                                    ( ( ( uint32_t ) configKERNEL_INTERRUPT_PRIORITY ) << 16UL )\r
+#define portNVIC_SYSTICK_PRI                           ( ( ( uint32_t ) configKERNEL_INTERRUPT_PRIORITY ) << 24UL )\r
 \r
-/* Constants required to check the validity of an interrupt prority. */\r
+/* Constants required to check the validity of an interrupt priority. */\r
 #define portFIRST_USER_INTERRUPT_NUMBER                ( 16 )\r
 #define portNVIC_IP_REGISTERS_OFFSET_16        ( 0xE000E3F0 )\r
-#define portAIRCR_REG                                          ( * ( ( volatile unsigned long * ) 0xE000ED0C ) )\r
+#define portAIRCR_REG                                          ( * ( ( volatile uint32_t * ) 0xE000ED0C ) )\r
+#define portMAX_8_BIT_VALUE                                    ( ( uint8_t ) 0xff )\r
+#define portTOP_BIT_OF_BYTE                                    ( ( uint8_t ) 0x80 )\r
+#define portMAX_PRIGROUP_BITS                          ( ( uint8_t ) 7 )\r
 #define portPRIORITY_GROUP_MASK                                ( 0x07UL << 8UL )\r
+#define portPRIGROUP_SHIFT                                     ( 8UL )\r
 \r
 /* Constants required to manipulate the VFP. */\r
-#define portFPCCR                                      ( ( volatile unsigned long * ) 0xe000ef34 ) /* Floating point context control register. */\r
+#define portFPCCR                                      ( ( volatile uint32_t * ) 0xe000ef34 ) /* Floating point context control register. */\r
 #define portASPEN_AND_LSPEN_BITS       ( 0x3UL << 30UL )\r
 \r
 /* Constants required to set up the initial stack. */\r
@@ -116,9 +126,18 @@ occurred while the SysTick counter is stopped during tickless idle
 calculations. */\r
 #define portMISSED_COUNTS_FACTOR                       ( 45UL )\r
 \r
+/* Let the user override the pre-loading of the initial LR with the address of\r
+prvTaskExitError() in case is messes up unwinding of the stack in the\r
+debugger. */\r
+#ifdef configTASK_RETURN_ADDRESS\r
+       #define portTASK_RETURN_ADDRESS configTASK_RETURN_ADDRESS\r
+#else\r
+       #define portTASK_RETURN_ADDRESS prvTaskExitError\r
+#endif\r
+\r
 /* Each task maintains its own interrupt status in the critical nesting\r
 variable. */\r
-static unsigned portBASE_TYPE uxCriticalNesting = 0xaaaaaaaa;\r
+static UBaseType_t uxCriticalNesting = 0xaaaaaaaa;\r
 \r
 /*\r
  * Setup the timer to generate the tick interrupts.  The implementation in this\r
@@ -144,13 +163,18 @@ static void prvPortStartFirstTask( void ) __attribute__ (( naked ));
  */\r
  static void vPortEnableVFP( void ) __attribute__ (( naked ));\r
 \r
+/*\r
+ * Used to catch tasks that attempt to return from their implementing function.\r
+ */\r
+static void prvTaskExitError( void );\r
+\r
 /*-----------------------------------------------------------*/\r
 \r
 /*\r
  * The number of SysTick increments that make up one tick period.\r
  */\r
 #if configUSE_TICKLESS_IDLE == 1\r
-       static unsigned long ulTimerCountsForOneTick = 0;\r
+       static uint32_t ulTimerCountsForOneTick = 0;\r
 #endif /* configUSE_TICKLESS_IDLE */\r
 \r
 /*\r
@@ -158,7 +182,7 @@ static void prvPortStartFirstTask( void ) __attribute__ (( naked ));
  * 24 bit resolution of the SysTick timer.\r
  */\r
 #if configUSE_TICKLESS_IDLE == 1\r
-       static unsigned long xMaximumPossibleSuppressedTicks = 0;\r
+       static uint32_t xMaximumPossibleSuppressedTicks = 0;\r
 #endif /* configUSE_TICKLESS_IDLE */\r
 \r
 /*\r
@@ -166,17 +190,18 @@ static void prvPortStartFirstTask( void ) __attribute__ (( naked ));
  * power functionality only.\r
  */\r
 #if configUSE_TICKLESS_IDLE == 1\r
-       static unsigned long ulStoppedTimerCompensation = 0;\r
+       static uint32_t ulStoppedTimerCompensation = 0;\r
 #endif /* configUSE_TICKLESS_IDLE */\r
 \r
 /*\r
- * Used by the portASSERT_IF_INTERRUPT_PRIORITY_INVALID() macro to ensure \r
+ * Used by the portASSERT_IF_INTERRUPT_PRIORITY_INVALID() macro to ensure\r
  * FreeRTOS API functions are not called from interrupts that have been assigned\r
  * a priority above configMAX_SYSCALL_INTERRUPT_PRIORITY.\r
  */\r
 #if ( configASSERT_DEFINED == 1 )\r
-        static unsigned char ucMaxSysCallPriority = 0;\r
-        static const volatile unsigned char * const pcInterruptPriorityRegisters = ( const volatile unsigned char * const ) portNVIC_IP_REGISTERS_OFFSET_16;\r
+        static uint8_t ucMaxSysCallPriority = 0;\r
+        static uint32_t ulMaxPRIGROUPValue = 0;\r
+        static const volatile uint8_t * const pcInterruptPriorityRegisters = ( const volatile uint8_t * const ) portNVIC_IP_REGISTERS_OFFSET_16;\r
 #endif /* configASSERT_DEFINED */\r
 \r
 /*-----------------------------------------------------------*/\r
@@ -184,7 +209,7 @@ static void prvPortStartFirstTask( void ) __attribute__ (( naked ));
 /*\r
  * See header file for description.\r
  */\r
-portSTACK_TYPE *pxPortInitialiseStack( portSTACK_TYPE *pxTopOfStack, pdTASK_CODE pxCode, void *pvParameters )\r
+StackType_t *pxPortInitialiseStack( StackType_t *pxTopOfStack, TaskFunction_t pxCode, void *pvParameters )\r
 {\r
        /* Simulate the stack frame as it would be created by a context switch\r
        interrupt. */\r
@@ -195,13 +220,13 @@ portSTACK_TYPE *pxPortInitialiseStack( portSTACK_TYPE *pxTopOfStack, pdTASK_CODE
 \r
        *pxTopOfStack = portINITIAL_XPSR;       /* xPSR */\r
        pxTopOfStack--;\r
-       *pxTopOfStack = ( portSTACK_TYPE ) pxCode;      /* PC */\r
+       *pxTopOfStack = ( StackType_t ) pxCode; /* PC */\r
        pxTopOfStack--;\r
-       *pxTopOfStack = 0;      /* LR */\r
+       *pxTopOfStack = ( StackType_t ) portTASK_RETURN_ADDRESS;        /* LR */\r
 \r
        /* Save code space by skipping register initialisation. */\r
        pxTopOfStack -= 5;      /* R12, R3, R2 and R1. */\r
-       *pxTopOfStack = ( portSTACK_TYPE ) pvParameters;        /* R0 */\r
+       *pxTopOfStack = ( StackType_t ) pvParameters;   /* R0 */\r
 \r
        /* A save method is being used that requires each task to maintain its\r
        own exec return value. */\r
@@ -214,6 +239,20 @@ portSTACK_TYPE *pxPortInitialiseStack( portSTACK_TYPE *pxTopOfStack, pdTASK_CODE
 }\r
 /*-----------------------------------------------------------*/\r
 \r
+static void prvTaskExitError( void )\r
+{\r
+       /* A function that implements a task must not exit or attempt to return to\r
+       its caller as there is nothing to return to.  If a task wants to exit it\r
+       should instead call vTaskDelete( NULL ).\r
+\r
+       Artificially force an assert() to be triggered if configASSERT() is\r
+       defined, then stop here so application writers can catch the error. */\r
+       configASSERT( uxCriticalNesting == ~0UL );\r
+       portDISABLE_INTERRUPTS();\r
+       for( ;; );\r
+}\r
+/*-----------------------------------------------------------*/\r
+\r
 void vPortSVCHandler( void )\r
 {\r
        __asm volatile (\r
@@ -222,6 +261,7 @@ void vPortSVCHandler( void )
                                        "       ldr r0, [r1]                                    \n" /* The first item in pxCurrentTCB is the task top of stack. */\r
                                        "       ldmia r0!, {r4-r11, r14}                \n" /* Pop the registers that are not automatically saved on exception entry and the critical nesting count. */\r
                                        "       msr psp, r0                                             \n" /* Restore the task stack pointer. */\r
+                                       "       isb                                                             \n"\r
                                        "       mov r0, #0                                              \n"\r
                                        "       msr     basepri, r0                                     \n"\r
                                        "       bx r14                                                  \n"\r
@@ -240,6 +280,8 @@ static void prvPortStartFirstTask( void )
                                        " ldr r0, [r0]                  \n"\r
                                        " msr msp, r0                   \n" /* Set the msp back to the start of the stack. */\r
                                        " cpsie i                               \n" /* Globally enable interrupts. */\r
+                                       " dsb                                   \n"\r
+                                       " isb                                   \n"\r
                                        " svc 0                                 \n" /* System call to start first task. */\r
                                        " nop                                   \n"\r
                                );\r
@@ -249,7 +291,7 @@ static void prvPortStartFirstTask( void )
 /*\r
  * See header file for description.\r
  */\r
-portBASE_TYPE xPortStartScheduler( void )\r
+BaseType_t xPortStartScheduler( void )\r
 {\r
        /* configMAX_SYSCALL_INTERRUPT_PRIORITY must not be set to 0.\r
        See http://www.FreeRTOS.org/RTOS-Cortex-M3-M4.html */\r
@@ -257,8 +299,9 @@ portBASE_TYPE xPortStartScheduler( void )
 \r
        #if( configASSERT_DEFINED == 1 )\r
        {\r
-               volatile unsigned long ulOriginalPriority;\r
-               volatile char * const pcFirstUserPriorityRegister = ( volatile char * const ) ( portNVIC_IP_REGISTERS_OFFSET_16 + portFIRST_USER_INTERRUPT_NUMBER );\r
+               volatile uint32_t ulOriginalPriority;\r
+               volatile uint8_t * const pucFirstUserPriorityRegister = ( volatile uint8_t * const ) ( portNVIC_IP_REGISTERS_OFFSET_16 + portFIRST_USER_INTERRUPT_NUMBER );\r
+               volatile uint8_t ucMaxPriorityValue;\r
 \r
                /* Determine the maximum priority from which ISR safe FreeRTOS API\r
                functions can be called.  ISR safe functions are those that end in\r
@@ -266,19 +309,35 @@ portBASE_TYPE xPortStartScheduler( void )
                ensure interrupt entry is as fast and simple as possible.\r
 \r
                Save the interrupt priority value that is about to be clobbered. */\r
-               ulOriginalPriority = *pcFirstUserPriorityRegister;\r
+               ulOriginalPriority = *pucFirstUserPriorityRegister;\r
+\r
+               /* Determine the number of priority bits available.  First write to all\r
+               possible bits. */\r
+               *pucFirstUserPriorityRegister = portMAX_8_BIT_VALUE;\r
 \r
-               /* Write the configMAX_SYSCALL_INTERRUPT_PRIORITY value to an interrupt\r
-               priority register. */\r
-               *pcFirstUserPriorityRegister = configMAX_SYSCALL_INTERRUPT_PRIORITY;\r
+               /* Read the value back to see how many bits stuck. */\r
+               ucMaxPriorityValue = *pucFirstUserPriorityRegister;\r
 \r
-               /* Read back the written priority to obtain its value as seen by the\r
-               hardware, which will only implement a subset of the priority bits. */\r
-               ucMaxSysCallPriority = *pcFirstUserPriorityRegister;\r
+               /* Use the same mask on the maximum system call priority. */\r
+               ucMaxSysCallPriority = configMAX_SYSCALL_INTERRUPT_PRIORITY & ucMaxPriorityValue;\r
+\r
+               /* Calculate the maximum acceptable priority group value for the number\r
+               of bits read back. */\r
+               ulMaxPRIGROUPValue = portMAX_PRIGROUP_BITS;\r
+               while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )\r
+               {\r
+                       ulMaxPRIGROUPValue--;\r
+                       ucMaxPriorityValue <<= ( uint8_t ) 0x01;\r
+               }\r
+\r
+               /* Shift the priority group value back to its position within the AIRCR\r
+               register. */\r
+               ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;\r
+               ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;\r
 \r
                /* Restore the clobbered interrupt priority register to its original\r
                value. */\r
-               *pcFirstUserPriorityRegister = ulOriginalPriority;\r
+               *pucFirstUserPriorityRegister = ulOriginalPriority;\r
        }\r
        #endif /* conifgASSERT_DEFINED */\r
 \r
@@ -302,6 +361,12 @@ portBASE_TYPE xPortStartScheduler( void )
        /* Start the first task. */\r
        prvPortStartFirstTask();\r
 \r
+       /* Should never get here as the tasks will now be executing!  Call the task\r
+       exit error function to prevent compiler warnings about a static function\r
+       not being called in the case that the application writer overrides this\r
+       functionality by defining configTASK_RETURN_ADDRESS. */\r
+       prvTaskExitError();\r
+\r
        /* Should not get here! */\r
        return 0;\r
 }\r
@@ -309,8 +374,9 @@ portBASE_TYPE xPortStartScheduler( void )
 \r
 void vPortEndScheduler( void )\r
 {\r
-       /* It is unlikely that the CM4F port will require this function as there\r
-       is nothing to return to.  */\r
+       /* Not implemented in ports where there is nothing to return to.\r
+       Artificially force an assert. */\r
+       configASSERT( uxCriticalNesting == 1000UL );\r
 }\r
 /*-----------------------------------------------------------*/\r
 \r
@@ -337,6 +403,7 @@ void vPortEnterCritical( void )
 \r
 void vPortExitCritical( void )\r
 {\r
+       configASSERT( uxCriticalNesting );\r
        uxCriticalNesting--;\r
        if( uxCriticalNesting == 0 )\r
        {\r
@@ -345,7 +412,7 @@ void vPortExitCritical( void )
 }\r
 /*-----------------------------------------------------------*/\r
 \r
-__attribute__(( naked )) unsigned long ulPortSetInterruptMask( void )\r
+__attribute__(( naked )) uint32_t ulPortSetInterruptMask( void )\r
 {\r
        __asm volatile                                                                                                          \\r
        (                                                                                                                                       \\r
@@ -362,7 +429,7 @@ __attribute__(( naked )) unsigned long ulPortSetInterruptMask( void )
 }\r
 /*-----------------------------------------------------------*/\r
 \r
-__attribute__(( naked )) void vPortClearInterruptMask( unsigned long ulNewMaskValue )\r
+__attribute__(( naked )) void vPortClearInterruptMask( uint32_t ulNewMaskValue )\r
 {\r
        __asm volatile                                                                                                  \\r
        (                                                                                                                               \\r
@@ -383,8 +450,9 @@ void xPortPendSVHandler( void )
        __asm volatile\r
        (\r
        "       mrs r0, psp                                                     \n"\r
+       "       isb                                                                     \n"\r
        "                                                                               \n"\r
-       "       ldr     r3, pxCurrentTCBConst                           \n" /* Get the location of the current TCB. */\r
+       "       ldr     r3, pxCurrentTCBConst                   \n" /* Get the location of the current TCB. */\r
        "       ldr     r2, [r3]                                                \n"\r
        "                                                                               \n"\r
        "       tst r14, #0x10                                          \n" /* Is the task using the FPU context?  If so, push high vfp registers. */\r
@@ -395,13 +463,13 @@ void xPortPendSVHandler( void )
        "                                                                               \n"\r
        "       str r0, [r2]                                            \n" /* Save the new top of stack into the first member of the TCB. */\r
        "                                                                               \n"\r
-       "       stmdb sp!, {r3, r14}                            \n"\r
+       "       stmdb sp!, {r3}                                         \n"\r
        "       mov r0, %0                                                      \n"\r
        "       msr basepri, r0                                         \n"\r
        "       bl vTaskSwitchContext                           \n"\r
        "       mov r0, #0                                                      \n"\r
        "       msr basepri, r0                                         \n"\r
-       "       ldmia sp!, {r3, r14}                            \n"\r
+       "       ldmia sp!, {r3}                                         \n"\r
        "                                                                               \n"\r
        "       ldr r1, [r3]                                            \n" /* The first item in pxCurrentTCB is the task top of stack. */\r
        "       ldr r0, [r1]                                            \n"\r
@@ -413,6 +481,15 @@ void xPortPendSVHandler( void )
        "       vldmiaeq r0!, {s16-s31}                         \n"\r
        "                                                                               \n"\r
        "       msr psp, r0                                                     \n"\r
+       "       isb                                                                     \n"\r
+       "                                                                               \n"\r
+       #ifdef WORKAROUND_PMU_CM001 /* XMC4000 specific errata workaround. */\r
+               #if WORKAROUND_PMU_CM001 == 1\r
+       "                       push { r14 }                            \n"\r
+       "                       pop { pc }                                      \n"\r
+               #endif\r
+       #endif\r
+       "                                                                               \n"\r
        "       bx r14                                                          \n"\r
        "                                                                               \n"\r
        "       .align 2                                                        \n"\r
@@ -444,10 +521,10 @@ void xPortSysTickHandler( void )
 \r
 #if configUSE_TICKLESS_IDLE == 1\r
 \r
-       __attribute__((weak)) void vPortSuppressTicksAndSleep( portTickType xExpectedIdleTime )\r
+       __attribute__((weak)) void vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime )\r
        {\r
-       unsigned long ulReloadValue, ulCompleteTickPeriods, ulCompletedSysTickDecrements;\r
-       portTickType xModifiableIdleTime;\r
+       uint32_t ulReloadValue, ulCompleteTickPeriods, ulCompletedSysTickDecrements, ulSysTickCTRL;\r
+       TickType_t xModifiableIdleTime;\r
 \r
                /* Make sure the SysTick reload value does not overflow the counter. */\r
                if( xExpectedIdleTime > xMaximumPossibleSuppressedTicks )\r
@@ -459,7 +536,7 @@ void xPortSysTickHandler( void )
                is accounted for as best it can be, but using the tickless mode will\r
                inevitably result in some tiny drift of the time maintained by the\r
                kernel with respect to calendar time. */\r
-               portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT;\r
+               portNVIC_SYSTICK_CTRL_REG &= ~portNVIC_SYSTICK_ENABLE_BIT;\r
 \r
                /* Calculate the reload value required to wait xExpectedIdleTime\r
                tick periods.  -1 is used because this code will execute part way\r
@@ -478,8 +555,16 @@ void xPortSysTickHandler( void )
                to be unsuspended then abandon the low power entry. */\r
                if( eTaskConfirmSleepModeStatus() == eAbortSleep )\r
                {\r
+                       /* Restart from whatever is left in the count register to complete\r
+                       this tick period. */\r
+                       portNVIC_SYSTICK_LOAD_REG = portNVIC_SYSTICK_CURRENT_VALUE_REG;\r
+\r
                        /* Restart SysTick. */\r
-                       portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;\r
+                       portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;\r
+\r
+                       /* Reset the reload register to the value required for normal tick\r
+                       periods. */\r
+                       portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;\r
 \r
                        /* Re-enable interrupts - see comments above the cpsid instruction()\r
                        above. */\r
@@ -495,7 +580,7 @@ void xPortSysTickHandler( void )
                        portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;\r
 \r
                        /* Restart SysTick. */\r
-                       portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;\r
+                       portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;\r
 \r
                        /* Sleep until something happens.  configPRE_SLEEP_PROCESSING() can\r
                        set its parameter to 0 to indicate that its implementation contains\r
@@ -516,19 +601,32 @@ void xPortSysTickHandler( void )
                        accounted for as best it can be, but using the tickless mode will\r
                        inevitably result in some tiny drift of the time maintained by the\r
                        kernel with respect to calendar time. */\r
-                       portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT;\r
+                       ulSysTickCTRL = portNVIC_SYSTICK_CTRL_REG;\r
+                       portNVIC_SYSTICK_CTRL_REG = ( ulSysTickCTRL & ~portNVIC_SYSTICK_ENABLE_BIT );\r
 \r
                        /* Re-enable interrupts - see comments above the cpsid instruction()\r
                        above. */\r
                        __asm volatile( "cpsie i" );\r
 \r
-                       if( ( portNVIC_SYSTICK_CTRL_REG & portNVIC_SYSTICK_COUNT_FLAG_BIT ) != 0 )\r
+                       if( ( ulSysTickCTRL & portNVIC_SYSTICK_COUNT_FLAG_BIT ) != 0 )\r
                        {\r
+                               uint32_t ulCalculatedLoadValue;\r
+\r
                                /* The tick interrupt has already executed, and the SysTick\r
                                count reloaded with ulReloadValue.  Reset the\r
                                portNVIC_SYSTICK_LOAD_REG with whatever remains of this tick\r
                                period. */\r
-                               portNVIC_SYSTICK_LOAD_REG = ( ulTimerCountsForOneTick - 1UL ) - ( ulReloadValue - portNVIC_SYSTICK_CURRENT_VALUE_REG );\r
+                               ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL ) - ( ulReloadValue - portNVIC_SYSTICK_CURRENT_VALUE_REG );\r
+\r
+                               /* Don't allow a tiny value, or values that have somehow\r
+                               underflowed because the post sleep hook did something\r
+                               that took too long. */\r
+                               if( ( ulCalculatedLoadValue < ulStoppedTimerCompensation ) || ( ulCalculatedLoadValue > ulTimerCountsForOneTick ) )\r
+                               {\r
+                                       ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL );\r
+                               }\r
+\r
+                               portNVIC_SYSTICK_LOAD_REG = ulCalculatedLoadValue;\r
 \r
                                /* The tick interrupt handler will already have pended the tick\r
                                processing in the kernel.  As the pending tick will be\r
@@ -556,15 +654,17 @@ void xPortSysTickHandler( void )
 \r
                        /* Restart SysTick so it runs from portNVIC_SYSTICK_LOAD_REG\r
                        again, then set portNVIC_SYSTICK_LOAD_REG back to its standard\r
-                       value. */\r
+                       value.  The critical section is used to ensure the tick interrupt\r
+                       can only execute once in the case that the reload register is near\r
+                       zero. */\r
                        portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;\r
-                       portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;\r
-\r
-                       vTaskStepTick( ulCompleteTickPeriods );\r
-\r
-                       /* The counter must start by the time the reload value is reset. */\r
-                       configASSERT( portNVIC_SYSTICK_CURRENT_VALUE_REG );\r
-                       portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;\r
+                       portENTER_CRITICAL();\r
+                       {\r
+                               portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;\r
+                               vTaskStepTick( ulCompleteTickPeriods );\r
+                               portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;\r
+                       }\r
+                       portEXIT_CRITICAL();\r
                }\r
        }\r
 \r
@@ -587,8 +687,8 @@ __attribute__(( weak )) void vPortSetupTimerInterrupt( void )
        #endif /* configUSE_TICKLESS_IDLE */\r
 \r
        /* Configure SysTick to interrupt at the requested rate. */\r
-       portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;;\r
-       portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;\r
+       portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;\r
+       portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT );\r
 }\r
 /*-----------------------------------------------------------*/\r
 \r
@@ -611,8 +711,8 @@ static void vPortEnableVFP( void )
 \r
        void vPortValidateInterruptPriority( void )\r
        {\r
-       unsigned long ulCurrentInterrupt;\r
-       unsigned char ucCurrentPriority;\r
+       uint32_t ulCurrentInterrupt;\r
+       uint8_t ucCurrentPriority;\r
 \r
                /* Obtain the number of the currently executing interrupt. */\r
                __asm volatile( "mrs %0, ipsr" : "=r"( ulCurrentInterrupt ) );\r
@@ -623,43 +723,46 @@ static void vPortEnableVFP( void )
                        /* Look up the interrupt's priority. */\r
                        ucCurrentPriority = pcInterruptPriorityRegisters[ ulCurrentInterrupt ];\r
 \r
-                       /* The following assertion will fail if a service routine (ISR) for \r
+                       /* The following assertion will fail if a service routine (ISR) for\r
                        an interrupt that has been assigned a priority above\r
                        configMAX_SYSCALL_INTERRUPT_PRIORITY calls an ISR safe FreeRTOS API\r
-                       function.  ISR safe FreeRTOS API functions must *only* be called \r
+                       function.  ISR safe FreeRTOS API functions must *only* be called\r
                        from interrupts that have been assigned a priority at or below\r
                        configMAX_SYSCALL_INTERRUPT_PRIORITY.\r
-                       \r
+\r
                        Numerically low interrupt priority numbers represent logically high\r
-                       interrupt priorities, therefore the priority of the interrupt must \r
-                       be set to a value equal to or numerically *higher* than \r
+                       interrupt priorities, therefore the priority of the interrupt must\r
+                       be set to a value equal to or numerically *higher* than\r
                        configMAX_SYSCALL_INTERRUPT_PRIORITY.\r
-                       \r
+\r
                        Interrupts that use the FreeRTOS API must not be left at their\r
                        default priority of     zero as that is the highest possible priority,\r
-                       which is guaranteed to be above configMAX_SYSCALL_INTERRUPT_PRIORITY, \r
-                       and     therefore also guaranteed to be invalid.  \r
-                       \r
-                       FreeRTOS maintains separate thread and ISR API functions to ensure \r
+                       which is guaranteed to be above configMAX_SYSCALL_INTERRUPT_PRIORITY,\r
+                       and     therefore also guaranteed to be invalid.\r
+\r
+                       FreeRTOS maintains separate thread and ISR API functions to ensure\r
                        interrupt entry is as fast and simple as possible.\r
-                       \r
+\r
                        The following links provide detailed information:\r
                        http://www.freertos.org/RTOS-Cortex-M3-M4.html\r
                        http://www.freertos.org/FAQHelp.html */\r
                        configASSERT( ucCurrentPriority >= ucMaxSysCallPriority );\r
                }\r
 \r
-               /* Priority grouping:  The interrupt controller (NVIC) allows the bits \r
-               that define each interrupt's priority to be split between bits that \r
+               /* Priority grouping:  The interrupt controller (NVIC) allows the bits\r
+               that define each interrupt's priority to be split between bits that\r
                define the interrupt's pre-emption priority bits and bits that define\r
-               the interrupt's sub-priority.  For simplicity all bits must be defined \r
+               the interrupt's sub-priority.  For simplicity all bits must be defined\r
                to be pre-emption priority bits.  The following assertion will fail if\r
-               this is not the case (if some bits represent a sub-priority).  \r
-               \r
-               If CMSIS libraries are being used then the correct setting can be \r
-               achieved by calling     NVIC_SetPriorityGrouping( 0 ); before starting the \r
-               scheduler. */\r
-               configASSERT( ( portAIRCR_REG & portPRIORITY_GROUP_MASK ) == 0 );\r
+               this is not the case (if some bits represent a sub-priority).\r
+\r
+               If the application only uses CMSIS libraries for interrupt\r
+               configuration then the correct setting can be achieved on all Cortex-M\r
+               devices by calling NVIC_SetPriorityGrouping( 0 ); before starting the\r
+               scheduler.  Note however that some vendor specific peripheral libraries\r
+               assume a non-zero priority group setting, in which cases using a value\r
+               of zero will result in unpredicable behaviour. */\r
+               configASSERT( ( portAIRCR_REG & portPRIORITY_GROUP_MASK ) <= ulMaxPRIGROUPValue );\r
        }\r
 \r
 #endif /* configASSERT_DEFINED */\r