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YIELD is a hint instruction. Software with a multithreading capability can use a YIELD instruction to indicate to the PE that it is performing a task, for example a spin-lock, that could be swapped out to improve overall system performance. The PE can use this hint to suspend and resume multiple software threads if it supports the capability.
For more information about the recommended use of this instruction, see The YIELD instruction.
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CRm | op2 |
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 '0000 111'
SEE "XPACLRI";
when '0001 xxx'
SEE "PACIA1716, PACIB1716, AUTIA1716, AUTIB1716";
when '0010 000'
if !HaveRASExt() then EndOfInstruction(); // Instruction executes as NOP
op = SystemHintOp_ESB;
when '0010 001'
if !HaveStatisticalProfiling() then EndOfInstruction(); // Instruction executes as NOP
op = SystemHintOp_PSB;
when '0010 010'
if !HaveSelfHostedTrace() then EndOfInstruction(); // Instruction executes as NOP
op = SystemHintOp_TSB;
when '0010 100'
op = SystemHintOp_CSDB;
when '0011 xxx'
SEE "PACIAZ, PACIASP, PACIBZ, PACIBSP, AUTIAZ, AUTIASP, AUTIBZ, AUTIBSP";
when '0100 xx0'
op = SystemHintOp_BTI;
// Check branch target compatibility between BTI instruction and PSTATE.BTYPE
// Check branch target compatibility
// between BTI instruction and PSTATE.BTYPE
BTypeCompatible = BTypeCompatible_BTI(op2<2:1>);
otherwise EndOfInstruction(); // Instruction executes as NOP
case op of
when SystemHintOp_YIELDHint_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 PSTATE.EL IN { ifEL2Enabled() && PSTATE.EL IN {EL0, EL1} &&} && ! EL2Enabled() && !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 PSTATE.EL IN { ifEL2Enabled() && PSTATE.EL IN {EL0, EL1} &&} && ! EL2Enabled() && !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_SEVSendEvent();
when SystemHintOp_SEVLSendEventLocal();
when SystemHintOp_ESBSynchronizeErrors();
AArch64.ESBOperation();
if PSTATE.EL IN { ifEL2Enabled() && PSTATE.EL IN {EL0, EL1} && EL2Enabled() then} then AArch64.vESBOperation();
TakeUnmaskedSErrorInterrupts();
when SystemHintOp_PSBProfilingSynchronizationBarrier();
when SystemHintOp_TSB
TraceSynchronizationBarrier();
when SystemHintOp_CSDBConsumptionOfSpeculativeDataBarrier();
when SystemHintOp_BTI
BTypeNext = '00';
otherwise // do nothing
Internal version only: isa v30.41v30.3, AdvSIMD v27.08v27.04, pseudocode r8p5_00bet2_rc5v85-xml-00bet9_rc1_1, sve v8.5-00bet10_rc5v8.5-00bet9_rc1
; Build timestamp: 2019-03-28T062018-12-12T11:3450
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This document is Non-Confidential.
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