3.7.9. The I and F bits

The I and F bits are the interrupt disable bits:

Software can use MSR, CPS, MOVS pc, SUBS pc, LDM ..,{..pc}^, or RFE instructions to change the values of the I and F bits. They are also set automatically by some exceptions.

When NMFIs are enabled, updates to the F bit are restricted. For more information see Non-maskable fast interrupts.

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