sysperfana/perfinvestigator/com.nokia.carbide.cpp.pi.doc.user/html/reference/methods/proc_mode.htm
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<h3>Processor Mode</h3>
<P LANG="en-GB" ALIGN=JUSTIFY>ARM processor architecture supports seven processor modes. Names of the modes are User, FIQ, IRQ, Supervisor, Abort, Undefined, and System. Purpose of the modes is to enable a suitably written operating system to control the use of certain system resources. On the other hand, the modes enable fast switching of context, for example, from user code to interrupt handling (see Banked Registers). All modes except the User mode are known as privileged modes. Of the privileged modes, all five modes except the System mode are known as exception modes. Exception modes are entered when an exception or an interrupt occurs. System mode can be used to control system resources from within the same register context as the user mode.</P>
<P LANG="en-GB" ALIGN=JUSTIFY>User mode can be changed to another mode only through an exception or an interrupt, making it possible to efficiently control the change between modes. In performance measurements, processor modes have a large importance since the processor mode indicates the status of processing within the system. When storing performance Related references in a part of the system that may be accessed with any of the processor modes active, it may be necessary to deduce from the processor mode whether certain operations are legal or not, and to proceed accordingly.</P>
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