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WFE

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:

It has encodings from the following instruction sets: A32 ( A1 ) and T32 ( T1 and T2 ) .

A1

313029282726252423222120191817161514131211109876543210
!= 1111001100100000(1)(1)(1)(1)(0)(0)(0)(0)00000010
cond

A1

WFE{<c>}{<q>}

// No additional decoding required

T1

1514131211109876543210
1011111100100000

T1

WFE{<c>}{<q>}

// No additional decoding required

T2

15141312111098765432101514131211109876543210
111100111010(1)(1)(1)(1)10(0)0(0)00000000010

T2

WFE{<c>}.W

// No additional decoding required

For more information about the constrained unpredictable behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors.

Assembler Symbols

<c>

See Standard assembler syntax fields.

<q>

See Standard assembler syntax fields.

Operation

if ConditionPassed() then
    EncodingSpecificOperations();
    if IsEventRegisterSet() then
        ClearEventRegister();
    else
        if PSTATE.EL == EL0 then
            // Check for traps described by the OS which may be EL1 or EL2.
            AArch32.CheckForWFxTrap(EL1, TRUE);
        if PSTATE.EL IN {EL0, EL1} && EL2Enabled() && !IsInHost() then
            // Check for traps described by the Hypervisor.
            AArch32.CheckForWFxTrap(EL2, TRUE);
        if HaveEL(EL3) && PSTATE.M != M32_Monitor then
            // Check for traps described by the Secure Monitor.
            AArch32.CheckForWFxTrap(EL3, TRUE);
        WaitForEvent();
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