Atmel SAM4S Series, Preliminary Data Sheet

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11100B–ATARM–31-Jul-12
SAM4S Series [Preliminary]
11.4.3 Exception Model
This section describes the exception model.
11.4.3.1 Exception States
Each exception is in one of the following states:
Inactive
The exception is not active and not pending.
Pending
The exception is waiting to be serviced by the processor.
An interrupt request from a peripheral or from software can change the state of the correspond-
ing interrupt to pending.
Active
An exception is being serviced by the processor but has not completed.
An exception handler can interrupt the execution of another exception handler. In this case, both
exceptions are in the active state.
Active and Pending
The exception is being serviced by the processor and there is a pending exception from the
same source.
11.4.3.2 Exception Types
The exception types are:
Reset
Reset is invoked on power up or a warm reset. The exception model treats reset as a special
form of exception. When reset is asserted, the operation of the processor stops, potentially at
any point in an instruction. When reset is deasserted, execution restarts from the address pro-
vided by the reset entry in the vector table. Execution restarts as privileged execution in Thread
mode.
Non Maskable Interrupt (NMI)
A non maskable interrupt (NMI) can be signalled by a peripheral or triggered by software. This is
the highest priority exception other than reset. It is permanently enabled and has a fixed priority
of -2.
NMIs cannot be:
• Masked or prevented from activation by any other exception.
• Preempted by any exception other than Reset.
Hard Fault
A hard fault is an exception that occurs because of an error during exception processing, or
because an exception cannot be managed by any other exception mechanism. Hard Faults
have a fixed priority of -1, meaning they have higher priority than any exception with configu-
rable priority.