6.2.2. Fault status information

When an abort occurs, information about the cause of the fault is recorded in a number of registers, depending on the type of abort:

Abort exceptions

The following registers are updated when any abort exception is taken:

Link Register

The r14_abt register is updated to provide information about the address of the instruction that the exception was taken on, in a similar way to other types of exception. This information can be used to resume program execution after the abort has been handled.

Note

When a prefetch abort has occurred, ARM recommends that you do not use the link register value for determining the aborting address, because 32-bit Thumb instructions do not have to be word aligned and can cause an abort on either halfword. This applies even if all of the code in the system does not use the extra 32-bit Thumb instructions introduced in ARMv6T2, because the earlier BL and BLX instructions are both 32 bits long.

Saved Program Status Register

The SPSR_abt register is updated to record the state and mode of the processor when the exception was taken, in a similar way to other types of exception.

Fault Status Register

There are two fault status registers, one for prefetch aborts (IFSR) and one for data aborts (DFSR). These record the type of abort that occurred, and whether it occurred on a read or a write. In particular, this enables the abort handler to distinguish between synchronous aborts, asynchronous aborts, and debug events.

Synchronous abort exceptions

The following register is updated when a synchronous abort exception is taken:

Fault Address Register

There are two fault address registers, one for prefetch aborts (IFAR) and one for data aborts (DFAR). These indicate the address of the memory access that caused the fault.

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