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11100B–ATARM–31-Jul-12
SAM4S Series [Preliminary]
11.9
System Control Block (SCB)
The System Control Block (SCB) provides system implementation information, and system con-
trol. This includes configuration, control, and reporting of the system exceptions.
Ensure that the software uses aligned accesses of the correct size to access the system control
block registers:
• except for the SCB_CFSR and SCB_SHPR1-SCB_SHPR3 registers, it must use aligned
word accesses
• for the SCB_CFSR and SCB_SHPR1-SCB_SHPR3 registers, it can use byte or aligned
halfword or word accesses.
The processor does not support unaligned accesses to system control block registers.
In a fault handler, to determine the true faulting address:
1.
Read and save the MMFAR or SCB_BFAR value.
2.
Read the MMARVALID bit in the MMFSR subregister, or the BFARVALID bit in the
BFSR subregister. The SCB_MMFAR or SCB_BFAR address is valid only if this bit is 1.
The software must follow this sequence because another higher priority exception might change
the SCB_MMFAR or SCB_BFAR value. For example, if a higher priority handler preempts the
current fault handler, the other fault might change the SCB_MMFAR or SCB_BFAR value.
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