Dear All, I am looking to clarify if alignment is required when using statically allocated tasks and, by extension, statically allocated stacks for Idle and Timers. I am currently using GCC with an NXP S32K144 EVK (ARM Cortex M4F). For example, I am currently allocating my tasks using the following pattern, following the examplies in the documentation: ~~~ // Does either StaticTaskt or StackTypet need to be aligned on 8-bytes? // This: #define ALIGN8BYTES // or this? #define ALIGN8BYTES attribute ((aligned (8)))

define STACKDEPTHFLASH_LED 256

static TaskHandlet xTaskHandleFlashLED; static StaticTaskt ALIGN8BYTES mxTaskBufferFlashLED; static StackTypet ALIGN8BYTES mxStackFlashLED[STACKDEPTHFLASH_LED];

define NOTHREADPARAMETERS NULL

xTaskHandleFlashLED = xTaskCreateStatic( vTaskFlashLED, “flashled”, STACKDEPTHFLASHLED, NOTHREADPARAMETERS, TASKPRIORITYFLASHLED, mxStackFlashLED, &mxTaskBuffer_FlashLED); ~~~ When looking at tasks.c for the dynamic case, the allocated memory will be aligned to (in the case of the CM4F) 8-byte boundaries, as guarunteed by pvPortAlloc: ~~~ { StackType_t *pxStack;

        /* Allocate space for the stack used by the task being created. */
        pxStack = pvPortMalloc( ( ( ( size_t ) usStackDepth ) * sizeof( StackType_t ) ) ); /*lint !e9079 All values returned by pvPortMalloc() have at least the alignment required by the MCU's stack and this allocation is the stack. */

        if( pxStack != NULL )
        {
            /* Allocate space for the TCB. */
            pxNewTCB = ( TCB_t * ) pvPortMalloc( sizeof( TCB_t ) ); /*lint !e9087 !e9079 All values returned by pvPortMalloc() have at least the alignment required by the MCU's stack, and the first member of TCB_t is always a pointer to the task's stack. */

            if( pxNewTCB != NULL )
            {
                /* Store the stack location in the TCB. */
                pxNewTCB->pxStack = pxStack;
            }
            else
            {
                /* The stack cannot be used as the TCB was not created.  Free
                it again. */
                vPortFree( pxStack );
            }
        }
        else
        {
            pxNewTCB = NULL;
        }
    }

~~~ As I understand it, The CM4F requires that the stack is 8-byte aligned. However, since StackTypet is a uint32t, then GCC will allocate this to a 4-byte boundary, not an 8-byte boundary, e.g. ~~~ .bss.mxTaskBufferFlashLED 0x000000002000435c 0x4c /tmp/ccRQFTy2.ltrans0.ltrans.o ~~~ So, should the statically allocated stack also be 8-byte aligned using gcc’s attribute ((aligned (8))) to ensure alignment? What is the likely consequence if this is not the case. Certainly, this does indeed force aligment: ~~~ fill 0x00000000200043c4 0x4 .bss.mxTaskBufferFlashLED 0x00000000200043c8 0x4c /tmp/ccPCqzB6.ltrans0.ltrans.o ~~~ And, would this be consequential for other statically alloctaed buffer, especially queues since the storage area is declared as a uint8_t: For example: ~~~

define DEBUGUARTQUEUE_SIZE 32

define DEBUGUARTQUEUEITEMSIZE sizeof(SUARTDatagram)

static QueueHandlet mqueue_DebugUART; static ALIGN8BYTES uint8t mqueueDebugUARTstorageArea[ DEBUGUARTQUEUESIZE * DEBUGUARTQUEUEITEM_SIZE]; static ALIGN8BYTES StaticQueuet mqueueDebugUARTStaticQueue; mqueueDebugUART = xQueueCreateStatic( DEBUGUARTQUEUESIZE, DEBUGUARTQUEUEITEMSIZE, mqueueDebugUARTstorageArea, &mqueueDebugUART_StaticQueue); ~~~ Kind regards, Damien.

You will probably find that the stack gets aligned within the xTaskCreateStatic() function – I can’t check myself right now but will do when I can. In the mean time if you see this is not the case then please let us know.

Just verified – the stack is aligned inside prvInitialiseNewTask(), and both xTaskCreate() and xTaskCreateStatic() call prvInitialiseNewTask().

Thanks very much! — Damien.