Posted on July 22, 2014 at 20:27> Code running in FLASH can see the entire memory space.
I thought that the MPU could disallow this. The app note has sample boot loader code that contains something like this:
/* Protected IP code Flash area */
MPU->RNR = some_region_number;
MPU->RBAR = starting_address_of_bootloader_flash;
MPU->RASR = PROTECTED_FLASH_SIZE| MPU_PRIVRW_UNPRIVNONE;
And similar lines to protect the DMA registers. I thought that these settings would cause any access from non-privileged (i.e. application) code to generate a mempry management (i.e. permission) fault, yet allow access from privileged (i.e. interrupt) code. If that is not the case, I guess I need to go back and re-read the CortexM4 docs, specifically section 4.2.1 in PM0214 ''STM32F4xxx Cortex M4 programming Manual''.
My question is that, *if* the above code really does prevent un-privileged code from accessing that portion of FLASH (or the DMA registers), how can I have an interrupt routine in the boot loader (which is privileged by virtue of the interrupt) change the privilege level before jumping to the application's interrupt routine. Changing the CONTROL bit 0 value has no effect when interrupt code is running.
