wfe

Wait For Event

WFE

Puts the processor into a low-power state until an event occurs.

Details

Puts the processor core into a low-power wait state until a wakeup event occurs (SEV, SEVL, or external interrupt). Execution resumes transparently at the next instruction. No condition flags are affected. Execution state: AArch64-only.

Pseudocode Operation

# Enter low-power state
while (no_event_pending) do
  wait_for_event
PC ← PC + 4

Example

WFE

Encoding

Binary Layout

11010101000000110010

0000

010

11111

Format System Alias

Opcode 0xD503205F

Extension Base

Operands

Reference (Arm A64 ISA)

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0xD503205F	WFE		A64		11010101000000110010 \| 0000 \| 010 \| 11111

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 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.

Operation

integer localtimeout = 1 << 64;    // No local timeout event is generated
Hint_WFE(localtimeout, WFxType_WFE);