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Last site update May 1 2013

vTaskAllocateMPURegions
[FreeRTOS-MPU Specific]

task. h 
void vTaskAllocateMPURegions( 
               xTaskHandle xTaskToModify, 
               const xMemoryRegion * const xRegions );

Memory regions are assigned to a restricted task when the task is created using a call to xTaskCreateRestricted(). The regions can then be modified or redefined at run time using vTaskAllocateMPURegions().

vTaskAllocateMPURegions() is intended for use with FreeRTOS-MPU, the demo applications for which contain an example of vTaskAllocateMPURegions() being used.

Parameters:
xTask The handle of the task being updated.
xRegions A pointer to an array of xMemoryRegion structures, each of which contains a single new memory region definitions. The array should be dimensioned using the constant portNUM_CONFIGURABLE_REGIONS, which on the ARM Cortex-M3 is set to 3.

xMemoryRegion is defined in task.h as: 


typedef struct xMEMORY_REGION
{
    void *pvBaseAddress;
    unsigned long ulLengthInBytes;
    unsigned long ulParameters;
} xMemoryRegion;


The pvBaseAddress and ulLengthInBytes members are self explanatory as the start of the memory region and the length of the memory region respectively. It is important to note that MPU regions must meet a number of constraints - in particular, the size and alignment of each region must both be equal to the same power of two value.

ulParameters defines how the task is permitted to access the memory region and can take the bitwise OR of the following values: 

    portMPU_REGION_READ_WRITE				
    portMPU_REGION_PRIVILEGED_READ_ONLY		
    portMPU_REGION_READ_ONLY				
    portMPU_REGION_PRIVILEGED_READ_WRITE	
    portMPU_REGION_CACHEABLE_BUFFERABLE		
    portMPU_REGION_EXECUTE_NEVER

Example usage (please refer to the FreeRTOS-MPU demo applications for a much more complete and comprehensive example): 



/* Define an array that the task will both read from and write to.  Make sure
the size and alignment are appropriate for an MPU region (note this uses GCC
syntax). */
static unsigned char ucOneKByte[ 1024 ] __attribute__((align( 1024 )));

/* Define an array of xMemoryRegion structures that configures an MPU region
allowing read/write access for 1024 bytes starting at the beginning of the
ucOneKByte array.  The other two of the maximum 3 definable regions are
unused so set to zero. */
static const xMemoryRegion xAltRegions[ portNUM_CONFIGURABLE_REGIONS ] =
{											
    /* Base address    Length    Parameters */
    { ucOneKByte,      1024,     portMPU_REGION_READ_WRITE },
    { 0,               0,        0 },
    { 0,               0,        0 }
};

void vATask( void *pvParameters )
{
    /* This task was created such that it has access to certain regions of
    memory as defined by the MPU configuration.  At some point it is 
    desired that these MPU regions are replaced with that defined in the
    xAltRegions const struct above.  Use a call to vTaskAllocateMPURegions()
    for this purpose.  NULL is used as the task handle to indicate that this
    function should modify the MPU regions of the calling task. */
    vTaskAllocateMPURegions( NULL, xAltRegions );
	
    /* Now the task can continue its function, but from this point on can only
    access its stack and the ucOneKByte array (unless any other statically
    defined or shared regions have been declared elsewhere). */
}






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