In mpu_armv7.h, why while loop is used in ARM_MPU_Load function which runs at every 4th iteration?

[nirajgandhi]

The following modified function does not work and it creates only four entries (Region 0 to Region 3). I am not able to understand the reason behind it. Why the while loop is used here and the iteration is decremented by MPU_TYPE_RALIASES ?

Here, MPU_TYPE_RALIASES is defined as 4U in core_cm7.h. and cnt is set to 12.

__STATIC_INLINE void ARM_MPU_Load(ARM_MPU_Region_t const* table, uint32_t cnt) 
{
  const uint32_t rowWordSize = sizeof(ARM_MPU_Region_t)/4U;
  /*while (cnt > MPU_TYPE_RALIASES) {
    ARM_MPU_OrderedMemcpy(&(MPU->RBAR), &(table->RBAR), MPU_TYPE_RALIASES*rowWordSize);
    table += MPU_TYPE_RALIASES;
    cnt -= MPU_TYPE_RALIASES;
  }*/
  ARM_MPU_OrderedMemcpy(&(MPU->RBAR), &(table->RBAR), cnt*rowWordSize);
}

[JonatanAntoni]

Hey @nirajgandhi,

ARM_MPU_Load has been implemented to load as many MPU regions as required with the least amount of CPU cycles.
Depending on the amount of region aliases of the MPU (MPU_TYPE_RALIASES) one can load as many regions with subsequent memory accesses at once.

Loading more MPU regions than MPU_TYPE_RALIASES one needs to split the load into junks. Hence your code won't work. It will only load the first 4 regions and the remaining 8 regions are written elsewhere into the memory. This gives basically undefined behaviour!

Cheers,
Jonatan