3.4. MMU faults and CPU aborts

The MMU generates an abort on the following types of faults:

In addition, an external abort can be raised by the external system. This can happen only for access types that have the core synchronized to the external system:

Alignment fault checking is enabled by the A bit in CP15 register 1. Alignment fault checking is not affected by whether or not the MMU is enabled. Translation, domain, and permission faults are only generated when the MMU is enabled.

The access control mechanisms of the MMU detect the conditions that produce these faults. If a fault is detected as a result of a memory access, the MMU aborts the access and signals the fault condition to the CPU core. The MMU retains status and address information about faults generated by the data accesses in the fault status register and fault address register (see Fault address and fault status registers). The MMU does not retain status about faults generated by instruction fetches.

An access violation for a given memory access inhibits any corresponding external access, with an abort returned to the CPU core.

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