wfit

Wait For Interrupt with Timeout

WFIT <Wn>

Waits for an interrupt or a timeout.

Pseudocode Operation

timeout ← Wn
while (timeout > 0 AND interrupt_not_pending()) {
  timeout ← timeout - 1
  enter_low_power_state()
}
Wn ← timeout

Example

WFIT w1

Encoding

Binary Layout

11010101000000110001

31:12

0000

11:8

001

7:5

4:0

Format System

Opcode 0xD5031020

Extension Base (v8.7)

Operands

Wn
Timeout

Reference

View in Arm A64 ISA Reference ↗ Arm A64 ISA

Instruction Forms

Encoding	Instruction		ISA		Bit pattern
0xD5031020	WFIT <Xt>		A64		11010101000000110001 \| 0000 \| 001 \| Rd

Description

Wait For Interrupt with Timeout is a hint instruction that indicates that the PE can enter a low-power state and remain there until either a local timeout event or a wakeup event occurs. For more information, see Wait For Interrupt. As described in Wait For Interrupt, the execution of a WFIT instruction that would otherwise cause entry to a low-power state can be trapped to a higher Exception level.

Operation

integer localtimeout = UInt(X[d, 64]);

if Halted() && ConstrainUnpredictableBool(Unpredictable_WFxTDEBUG) then
    EndOfInstruction();

Hint_WFI(localtimeout, WFxType_WFIT);