wait

Wait

WAIT

Wait for FPU (same as FWAIT).

Pseudocode Operation

while (FPU_busy_flag == 1) {
  stall();
}

Encoding

Binary Layout

9B

+0

 

Format Legacy

Opcode 9B

Extension Base

Operands

Related

More in Base

Reference

View in Intel® 64 and IA-32 Architectures SDM ↗ Intel® SDM

Instruction Forms

Opcode	Instruction	Op/En	64/32-bit Mode	CPUID	Description
9B	WAIT	ZO	Valid Valid		Check pending unmasked floating-point exceptions.
9B	FWAIT	ZO	Valid Valid		Check pending unmasked floating-point exceptions.

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;

Exceptions

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. WAIT/FWAIT-Wait Vol. 2D 6-1