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

SystemHintOp op; case CRm:op2 of when '0000 000' op = SystemHintOp_NOP; when '0000 001' op = SystemHintOp_YIELD; when '0000 010' op = SystemHintOp_WFE; when '0000 011' op = SystemHintOp_WFI; when '0000 100' op = SystemHintOp_SEV; when '0000 101' op = SystemHintOp_SEVL; when '0010 000' op = if HaveRASExt() then SystemHintOp_ESB else SystemHintOp_NOP; when '0010 001' op = if HaveStatisticalProfiling() then SystemHintOp_PSB else SystemHintOp_NOP; otherwise op = SystemHintOp_NOP;

Operation

case op of when SystemHintOp_YIELD Hint_Yield(); when SystemHintOp_WFE 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 HaveEL(EL2) && !IsSecure() && 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(); when SystemHintOp_WFI if !InterruptPending() then if PSTATE.EL == EL0 then // Check for traps described by the OS which may be EL1 or EL2. AArch64.CheckForWFxTrap(EL1, FALSE); if HaveEL(EL2) && !IsSecure() && PSTATE.EL IN {EL0,EL1} && !IsInHost() then // Check for traps described by the Hypervisor. AArch64.CheckForWFxTrap(EL2, FALSE); if HaveEL(EL3) && PSTATE.EL != EL3 then // Check for traps described by the Secure Monitor. AArch64.CheckForWFxTrap(EL3, FALSE); WaitForInterrupt(); when SystemHintOp_SEV SendEvent(); when SystemHintOp_SEVL SendEventLocal(); when SystemHintOp_ESB ErrorSynchronizationBarrier(MBReqDomain_FullSystem, MBReqTypes_All); AArch64.ESBOperation(); if HaveEL(EL2) && !IsSecure() && PSTATE.EL IN {EL0,EL1} then AArch64.vESBOperation(); TakeUnmaskedSErrorInterrupts(); when SystemHintOp_PSB ProfilingSynchronizationBarrier(); otherwise // do nothing


Internal version only: isa v25.07, AdvSIMD v23.0, pseudocode v31.3

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