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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 mechanism and Send event.

As described in Wait For Event mechanism 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:

313029282726252423222120191817161514131211109876543210
11010101000000110010000001011111
CRmop2

System

WFE

// Empty.

Operation

if IsEventRegisterSet() then
    ClearEventRegister();
else
    if PSTATE.EL == EL0 then
        // Check for traps described by the OS which may be EL1 or EL2.
        AArch64.CheckForWFxTrap(EL1, TRUE);
    if EL2Enabled() && PSTATE.EL IN {EL0, EL1} && !IsInHost() then
        // Check for traps described by the Hypervisor.
        AArch64.CheckForWFxTrap(EL2, TRUE);
    if HaveEL(EL3) && PSTATE.EL != EL3 then
        // Check for traps described by the Secure Monitor.
        AArch64.CheckForWFxTrap(EL3, TRUE);
    WaitForEvent();
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