After facing some weird stability issues on the STM32F7 we have setup the MPU according to the recommendations presented in "MPU usage in STM32 with ARM CortexM7":
As far as I understand, the key point is to prevent speculative execution fetch from ExternalRAM and ExternalDevice memory regions. This is done by setup a 4GB wide low priority region and then enabling only some sub-regions (0x87) to have a range from 0x6000 0000 to 0xDFFF FFFF:
Since MPU_PRIVILEDGED_DEFAULT is enabled in this example, for all disabled subsections of the MPU_REGION_NUMBER0 the default memorymap will be active (privileged access only).
My question is: Could the speculative access also be prevented by disabling the privileged default memory map (PRIVDEFENA = 0). This would disallow all access (R/W) to the whole memory range at first. Memory areas used by the application would then have to be added defining separate MPU regions.
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