wfi

Wait For Interrupt (Thumb)

WFI

Wait for interrupt (Thumb).

Pseudocode Operation

WaitForInterrupt()

Encoding

Binary Layout

10111111

15:8

0011

7:4

0000

3:0

Format Thumb System

Opcode 0xBF30

Extension T32 (Base)

Operands

Other forms of wfi

wfi Wait For Interrupt
wfi Wait For Interrupt (A32)

Reference

View in Arm A64 ISA Reference ↗ Arm AArch32 ISA

Instruction Forms

Encoding	Instruction	ISA	Bit pattern
0x0320F003	WFI{<c>}{<q>}	A32	cond \| 00110 \| 0 \| 10 \| 00 \| 00 \| 1 \| 1 \| 1 \| 1 \| 000000000011
0xBF30	WFI{<c>}{<q>}	T32	10111111 \| 0011 \| 0000
0xF3AF8003	WFI{<c>}.W	T32	111100111010 \| 1 \| 1 \| 1 \| 1 \| 10 \| 0 \| 0 \| 0 \| 000 \| 0000 \| 0011

Description

Wait For Interrupt is a hint instruction that indicates that the PE can enter a low-power state and remain there until a wakeup event occurs. For more information, see Wait For Interrupt. As described in Wait For Interrupt, the execution of a WFI instruction that would otherwise cause entry to a low-power state can be trapped to a higher Exception level, see:

Operation

if ConditionPassed() then
    EncodingSpecificOperations();
    if !InterruptPending() then
        if PSTATE.EL == EL0 then
            // Check for traps described by the OS.
            AArch32.CheckForWFxTrap(EL1, WFxType_WFI);
        if PSTATE.EL IN {EL0, EL1} && EL2Enabled() && !IsInHost() then
            // Check for traps described by the Hypervisor.
            AArch32.CheckForWFxTrap(EL2, WFxType_WFI);
        if HaveEL(EL3) && PSTATE.M != M32_Monitor then
            // Check for traps described by the Secure Monitor.
            AArch32.CheckForWFxTrap(EL3, WFxType_WFI);
        integer localtimeout = 1 << 64;  // No local timeout event is generated
        WaitForInterrupt(localtimeout);

wfi