wfe

Wait For Event (Thumb)

WFE

Wait for event (Thumb).

Pseudocode Operation

if EventRegister == 1 then
  EventRegister ← 0
else
  WaitForEvent()
  EventRegister ← 0

Encoding

Binary Layout

10111111

15:8

0010

7:4

0000

3:0

Format Thumb System

Opcode 0xBF20

Extension T32 (Base)

Operands

Other forms of wfe

wfe Wait For Event
wfe Wait For Event (A32)

Reference

View in Arm A64 ISA Reference ↗ Arm AArch32 ISA

Instruction Forms

Encoding	Instruction	ISA	Bit pattern
0x0320F002	WFE{<c>}{<q>}	A32	cond \| 00110 \| 0 \| 10 \| 00 \| 00 \| 1 \| 1 \| 1 \| 1 \| 000000000010
0xBF20	WFE{<c>}{<q>}	T32	10111111 \| 0010 \| 0000
0xF3AF8002	WFE{<c>}.W	T32	111100111010 \| 1 \| 1 \| 1 \| 1 \| 10 \| 0 \| 0 \| 0 \| 000 \| 0000 \| 0010

Description

Wait For Event is a hint instruction that indicates that the PE can enter a low-power state and remain there until a wakeup event occurs. Wakeup events include the event signaled as a result of executing the SEV instruction on any PE in the multiprocessor system. For more information, see Wait For Event and Send Event. As described in Wait For Event and Send Event, the execution of a WFE 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 IsEventRegisterSet() then
        ClearEventRegister();
    else
        if PSTATE.EL == EL0 then
            // Check for traps described by the OS.
            AArch32.CheckForWFxTrap(EL1, WFxType_WFE);
        if PSTATE.EL IN {EL0, EL1} && EL2Enabled() && !IsInHost() then
            // Check for traps described by the Hypervisor.
            AArch32.CheckForWFxTrap(EL2, WFxType_WFE);
        if HaveEL(EL3) && PSTATE.M != M32_Monitor then
            // Check for traps described by the Secure Monitor.
            AArch32.CheckForWFxTrap(EL3, WFxType_WFE);
        integer localtimeout = 1 << 64;  // No local timeout event is generated
        WaitForEvent(localtimeout);

wfe