# WAIT/FWAIT — Wait

Opcode | Instruction | Op/En | 64-Bit Mode | Compat/Leg Mode | Description
--- | --- | --- | --- | --- | ---
9B | WAIT | ZO | Valid | Valid | Check pending unmasked floating-point exceptions.
9B | FWAIT | ZO | Valid | Valid | Check pending unmasked floating-point exceptions.

## Instruction Operand Encoding ¶

Op/En | Operand 1 | Operand 2 | Operand 3 | Operand 4
--- | --- | --- | --- | ---
ZO | N/A | N/A | N/A | N/A

## Description ¶

Causes the processor to check for and handle pending, unmasked, floating-point exceptions before proceeding. (FWAIT is an alternate mnemonic for WAIT.)

This instruction is useful for synchronizing exceptions in critical sections of code. Coding a WAIT instruction after a floating-point instruction ensures that any unmasked floating-point exceptions the instruction may raise are handled before the processor can modify the instruction’s results. See the section titled “Floating-Point Exception Synchronization” in Chapter 8 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, for more information on using the WAIT/FWAIT instruction.

This instruction’s operation is the same in non-64-bit modes and 64-bit mode.

## Operation ¶

    CheckForPendingUnmaskedFloatingPointExceptions;

## FPU Flags Affected ¶

The C0, C1, C2, and C3 flags are undefined.

## Floating-Point Exceptions ¶

None.

## Protected Mode Exceptions ¶

#NM | If CR0.MP[bit 1] = 1 and CR0.TS[bit 3] = 1.
#UD | If the LOCK prefix is used.

## Real-Address Mode Exceptions ¶

Same exceptions as in protected mode.

## Virtual-8086 Mode Exceptions ¶

Same exceptions as in protected mode.

## Compatibility Mode Exceptions ¶

Same exceptions as in protected mode.

## 64-Bit Mode Exceptions ¶

Same exceptions as in protected mode.