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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 110' if !HaveDGHExt() then EndOfInstruction(); // Instruction executes as NOP op = SystemHintOp_DGH; when '0000 111' SEE "XPACLRI"; when '0001 xxx' case op2 of when '000' SEE "PACIA1716"; when '010' SEE "PACIB1716"; when '100' SEE "AUTIA1716"; when '110' SEE "AUTIB1716"; otherwise EndOfInstruction(); // Instruction executes as NOP 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' case op2 of when '000' SEE "PACIAZ"; when '001' SEE "PACIASP"; when '010' SEE "PACIBZ"; when '011' SEE "PACIBSP"; when '100' SEE "AUTIAZ"; when '101' SEE "AUTHASP"; when '110' SEE "AUTIBZ"; when '111' SEE "AUTIBSP"; when '0100 xx0' op = SystemHintOp_BTI; // Check branch target compatibility between BTI instruction and PSTATE.BTYPE SetBTypeCompatible(BTypeCompatible_BTI(op2<2:1>)); otherwise EndOfInstruction(); // Instruction executes as NOP
case op of
when SystemHintOp_YIELDHint_Yield();
when SystemHintOp_DGHHint_DGH();
when SystemHintOp_WFE
integer localtimeout = -1; // No local timeout event is generated
Hint_WFE(localtimeout,(localtimeout);
when WFxType_WFE);
when SystemHintOp_WFI
integer localtimeout = -1; // No local timeout event is generated
Hint_WFI(localtimeout, WFxType_WFI);
(localtimeout);
when SystemHintOp_SEVSendEvent();
when SystemHintOp_SEVLSendEventLocal();
when SystemHintOp_ESB
if HaveTME() && TSTATE.depth > 0 then
FailTransaction(TMFailure_ERR, FALSE);
SynchronizeErrors();
AArch64.ESBOperation();
if PSTATE.EL IN {EL0, EL1} && EL2Enabled() then AArch64.vESBOperation();
TakeUnmaskedSErrorInterrupts();
when SystemHintOp_PSBProfilingSynchronizationBarrier();
when SystemHintOp_TSBTraceSynchronizationBarrier();
when SystemHintOp_CSDBConsumptionOfSpeculativeDataBarrier();
when SystemHintOp_BTISetBTypeNext('00');
otherwise // do nothing
Internal version only: isa v32.13v32.12, AdvSIMD v29.05v29.04, pseudocode v2020-12v2020-09_xml, sve v2020-12v2020-09_rc2b
; Build timestamp: 2020-12-16T142020-09-30T19:4116
Copyright © 2010-2020 Arm Limited or its affiliates. All rights reserved. This document is Non-Confidential.
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