Specifications

There are two kinds of MPU region violation exceptions:
• MPU region violation (instruction)—Any instruction fetch can cause this exception.
• MPU region violation (data)—Load, store, initda, and flushda instructions can cause this exception.
The general exception handler can inspect the exception.CAUSE field to determine which kind of MPU
region violation exception occurred.
Other Exceptions
The preceding sections describe all of the exception types defined by the Nios II architecture at the time of
publishing. However, some processor implementations might generate exceptions that do not fall into the
categories listed in the preceding sections. Therefore, a robust exception handler must provide a safe
response (such as issuing a warning) in the event that it cannot identify the cause of an exception.
Exception Processing Flow
Except for the break exception (refer to the Processing a Break section of this chapter), this section
describes how the processor responds to exceptions, including interrupts and instruction-related
exceptions.
Related Information
• Exception Handling
For details about writing programs to take advantage of exception and interrupt handling, refer to the
Exception Handling chapter of the Nios II Software Developer’s Handbook.
• Processing a Break on page 3-40
Processing General Exceptions
The general exception handler is a routine that determines the cause of each exception (including the
double TLB miss exception), and then dispatches an exception routine to respond to the exception. The
address of the general exception handler, specified with the Nios II Processor parameter editor in Qsys, is
called the exception vector in the Nios II Processor parameter editor. At run time this address is fixed, and
software cannot modify it. Programmers do not directly access exception vectors, and can write programs
without awareness of the address.
Note:
If the EIC interface is present, the general exception handler processes only noninterrupt
exceptions.
The fast TLB miss exception handler only handles the fast TLB miss exception. It is built for speed to
process TLB misses quickly. The fast TLB miss exception handler address, specified with the Nios II
Processor parameter editor in Qsys, is called the fast TLB miss exception vector in the Nios II Processor
parameter editor.
Exception Flow with the EIC Interface
If the EIC interface is present, interrupt processing differs markedly from noninterrupt exception
processing. The EIC interface provides the following information to the Nios II processor for each
interrupt request:
NII51003
2015.04.02
Other Exceptions
3-49
Programming Model
Altera Corporation
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