Heap Memory and large Array allocation

Hi guys,

I’m sure that is not a valid concern, but I prefer to have an answer by those who have more experience than me.

I’m using FreeRTOS 9.0 and heap_4.c for heap memory management.

In order to simplify my question, let us imagine that we use a 8-bit processor (so, a word is a byte)

Now, I need to create a task after creating and deleting another tasks (so, my heap memory can be a little bit fragmented):

ReturnState = xTaskCreate( MyTask,
( char * ) “MyTask”,
( void * ) NULL,

Of course, the configTOTAL_HEAP_SIZE is large enough for another task.

MyTask code is the following:

void MyTask( void *pvParameters )
 uint8_t MyArray[3*configMINIMAL_STACK_SIZE];

 memset((void *)&MyArray[0],0xA5,sizeof(MyArray));

 printf("The last number of my array is: %d",MyArray[3*configMINIMAL_STACK_SIZE-1]);

 for(;;;) __asm('NOP');

In MyTask I’ve created an array with size larger than configMINIMAL_STACK_SIZE. If heap memory is fragmented, FreeRTOS ensure me that the MyArray is allocated to a single memory block ?

Thanks for your reply.



FreeRTOS is not responsible the binary layout of MyArray it‘s just the C/C++ standard.
The same would apply to allocating MyArray from heap provided the heap implementation is standard compliant.
In your case yes, MyArray is contiguous, which can be verified with
sizeof(MyArray) == sizeof(MyArray[0]) * 3*configMINIMAL_STACK_SIZE
because there is no alignment constraint with uint8_t elements.

BTW I’m pretty sure that your code will fail with stack overflow because of using pretty stack hungry printf.

The FreeRTOS memory allocation routines can only return the requested memory as a contiguous block, or they will fail and return NULL. If the heap gets too fragmented you get allocation failures, not some strange way to return a disjointed block of memory.

Dear Richard and Hartmut.

Thanks for your reply, you have confirmed to me the behavior that I expected.