UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 3 — 20 December 2013 783 of 841
NXP Semiconductors
UM10360
Chapter 34: Appendix: Cortex-M3 user guide
When an unaligned access faults the address in the BFAR is the one requested by the
instruction, even if it is not the address of the fault.
Flags in the BFSR indicate the cause of the fault, and whether the value in the BFAR is
valid. See Table 669
.
34.4.3.15 System control block design hints and tips
Ensure software uses aligned accesses of the correct size to access the system control
block registers:
• except for the CFSR and SHPR1-SHPR3, it must use aligned word accesses
• for the CFSR and SHPR1-SHPR3 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 BFAR value.
2. Read the MMARVALID bit in the MMFSR, or the BFARVALID bit in the BFSR. The
MMFAR or BFAR address is valid only if this bit is 1.
Software must follow this sequence because another higher priority exception might
change the MMFAR or BFAR value. For example, if a higher priority handler preempts the
current fault handler, the other fault might change the MMFAR or BFAR value.
Table 673. BFAR bit assignments
Bits Name Function
[31:0] ADDRESS When the BFARVALID bit of the BFSR is set to 1, this field holds the
address of the location that generated the bus fault
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