wait

Wait for Interrupt

wait WC,PL

Stops instruction execution and places the processor in a lower power state until an interrupt occurs.

Encoding

Binary Layout

0:5

6:10

11:15

16:20

21:30

Format X-form

Opcode 0x7C00003C

Extension Base

Operands

WC
Wait Condition (0=Interrupt, 1=Resume)
PL
Programmable Length Field

Example

wait 0

// Idle CPU.

Reference

View in PowerISA v3.1C Specification ↗ OPF Power ISA v3.1C

Description

Suspends instruction execution and places the processor in a low-power idle state until an interrupt is pending. The WC field selects the wait condition (interrupt vs. resume), and the PL field optionally specifies a programmable length timeout. This is a Base/privileged instruction with no effect on condition registers; execution resumes after the specified event.

Operation

if WC == 0 then
  WaitForInterrupt()
else if WC == 1 then
  WaitForResume()

Extended Mnemonics

Extended Mnemonic	Equivalent Instruction
waitrsv
pause_short

Programming Note

Because the waiting begins when the instruction completes, if the waiting is ended by an exception that causes a change of control flow (interrupt, event-based branch), the SPR that is set to reflect the point in the instruction stream at which the change of control flow occurred (e.g., SRR0 for Decrementer interrupt) will contain the EA of the instruction following the wait instruction. Bits 6 and 7 of the wait instruction may be used in some implementations for an implementation-dependent field. Unless the intention is to use the implementation-dependent field, these bits must be coded zero. wait serves as both a basic and an extended mnemonic. The Assembler will recognize a wait mnemonic with two operands as the basic form and a wait mnemonic with one operand or with no operand as an extended form. In the extended form with one operand the PL operand is omitted and assumed to be 0. In the extended form with no operand the WC and PL operands are omitted and assumed to be 0. The wait instruction frees computational resources which might be allocated to another program or converted into power savings.