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[Default]

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This option specifies the general registers which are to be used only in fast interrupt functions (functions that have the fast interrupt setting (fint) in their interrupt specification defined by #pragma interrupt). The specified registers cannot be used in functions other than the fast interrupt functions. Since the general registers specified by this option can be used without being saved or restored in fast interrupt functions, the execution speed of fast interrupt functions will most likely be improved. Then again, since the number of usable general registers in other functions is reduced, the efficiency of register allocation in the entire program is degraded.

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The options correspond to the registers as shown in the following table.

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Correct operation is not guaranteed when a register specified by this option is used in a function other than the fast interrupt functions. If a register specified by this option has been specified by the base option, an error will occur.