FPEXC, the floating-point exception register

You can only access the FPEXC in privileged software execution. It contains the following bits:

bit[31]

Is the EX bit. You can read it in all NEON or VFP implementations. In some implementations you might also be able to write to it.

If the value is 0, the only significant state in the NEON or VFP system is the contents of the general-purpose registers plus FPSCR and FPEXC.

If the value is 1, you require implementation-specific information to save state.

bit[30]

Is the EN bit. You can read and write it in all NEON or VFP implementations.

If the value is 1, NEON (if present) and VFP (if present) are enabled and operate normally.

If the value is 0, NEON and VFP are disabled. When they are disabled, you can read or write the FPSID or FPEXC registers, but other NEON or VFP instructions are treated as Undefined Instructions.

bits[29:0]

Might be used by particular implementations of VFP. You can use the VFP instructions without accessing these bits.

You must not alter these bits except in accordance with their use in a particular implementation.

To change some bits without affecting other bits, use a read-modify-write procedure.

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