
EM358x
Rev. 0.4
25
3.4 Faults
Four of the exceptions in the NVIC are faults: Hard Fault, Memory Fault, Bus Fault, and Usage Fault. Of these,
three (Hard Fault, Memory Fault, and Usage Fault) are standard ARM
®
Cortex
TM
-M3 exceptions.
The Bus Fault, though, is derived from EM358x-specific sources. The Bus Fault sources are recorded in the
SCS_AFSR register. Note that it is possible for one access to set multiple SCS_AFSR bits. Also note that MPU
configurations could prevent most of these bus fault accesses from occurring, with the advantage that illegal
writes are made precise faults. The four bus faults are:
WRONGSIZE – Generated by an 8-bit or 16-bit read or write of an APB peripheral register. This fault can also
result from an unaligned 32-bit access.
PROTECTED – Generated by a user mode (unprivileged) write to a system APB or AHB peripheral or
protected RAM (see Chapter 2, Section 2.2.2.3).
RESERVED – Generated by a read or write to an address within an APB peripheral’s 4 kB block range, but
the address is above the last physical register in that block range. Also generated by a read or write to an
address above the top of RAM or flash.
MISSED – Generated by a second SCS_AFSR fault. In practice, this bit is not seen since a second fault also
generates a hard fault, and the hard fault preempts the bus fault.
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