ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

An exception is described as synchronous if both of the following apply:
The System Level Programmers’ Model
— the exception is generated as a result of direct execution or attempted execution of the
instruction stream
— the return address presented to the exception handler is guaranteed to indicate the instruction
that caused the exception.
An exception is described as asynchronous if either of the following applies:
— the exception is not generated as a result of direct execution or attempted execution of the
instruction stream
— the return address presented to the exception handler is not guaranteed to indicate the
instruction that caused the exception.
Asynchronous exceptions are of two types:
a precise asynchronous exception guarantees that the state presented to the exception handler is
consistent with the state at an identifiable instruction boundary in the execution stream from which
the exception was taken.
an imprecise asynchronous exception is one where the state presented to the exception handler is not
guaranteed to be consistent with any point in the execution stream from which the exception was
taken.
ARM DDI 0406B Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. B1-5