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:
- Traps to Undefined mode of PL0 execution of WFE and WFI instructions.
- Traps to Hyp mode of Non-secure EL0 and EL1 execution of WFE and WFI instructions.
- Traps to Monitor mode of the execution of WFE and WFI instructions in modes other than Monitor mode.
It has encodings from the following instruction sets: A32 ( A1 ) and T32 ( T1 and T2 ) .
A1
31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
!= 1111 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | (1) | (1) | (1) | (1) | (0) | (0) | (0) | (0) | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | |||
cond |
// No additional decoding required
T1
15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
// No additional decoding required
T2
15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 0 | 1 | 0 | (1) | (1) | (1) | (1) | 1 | 0 | (0) | 0 | (0) | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 |
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
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();