mwaitx

Monitor Wait Extended

MWAITX

Waits for a write to monitored address (AMD extension).

Pseudocode Operation

while (memory[monitor_address] has not been written) {
  if (ECX[1] == 1 && timeout_expired(EDX)) break
  if (interrupt_pending()) break
  wait()
}

Encoding

Binary Layout

0F

+0

01

+1

FB

+2

 

Format AMD

Opcode 0F 01 FB

Extension AMD

Operands

Related

More in AMD

Reference

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

Instruction Forms

Opcode	Instruction	Op/En	64/32-bit Mode	CPUID	Description
0F 01 FB	MWAITX				Causes the processor to stop instruction execution until a store to the monitored address range occurs, an interrupt is received, or (if enabled via ECX bit 1) a timeout in EBX expires.

Description

Waits for a store to the address range armed by MONITORX, or until the optional EBX timeout elapses. AMD-specific counterpart to MWAIT (Intel MWAIT uses SSE3's 0F 01 C9; MWAITX is a distinct AMD encoding, 0F 01 FB, with the added timeout capability).