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# CP15ISB, Instruction Synchronization Barrier System instruction

The CP15ISB characteristics are:

## Purpose

Performs an Instruction Synchronization Barrier.

Arm deprecates any use of this System instruction, and strongly recommends that software use the ISB instruction instead.

## Configuration

This instruction is present only when AArch32 is supported. Otherwise, direct accesses to CP15ISB are UNDEFINED.

## Attributes

CP15ISB is a 32-bit System instruction.

## Field descriptions

This instruction has no applicable fields.

The value in the register specified by <Rt> is ignored.

## Executing CP15ISB

Accesses to this instruction use the following encodings in the System instruction encoding space:

#### MCR{<c>}{<q>} <coproc>, {#}<opc1>, <Rt>, <CRn>, <CRm>{, {#}<opc2>}

coproc | opc1 | CRn | CRm | opc2
--- | --- | --- | --- | ---
0b1111 | 0b000 | 0b0111 | 0b0101 | 0b100

if PSTATE.EL == EL0 then if !ELUsingAArch32(EL1) && !ELIsInHost(EL0) && SCTLR_EL1.CP15BEN == '0' then UNDEFINED; elsif ELIsInHost(EL0) && SCTLR_EL2.CP15BEN == '0' then UNDEFINED; elsif ELUsingAArch32(EL1) && SCTLR.CP15BEN == '0' then UNDEFINED; elsif EL2Enabled() && !ELUsingAArch32(EL2) && !ELIsInHost(EL0) && HSTR_EL2.T7 == '1' then AArch64.AArch32SystemAccessTrap(EL2, 0x03); elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T7 == '1' then AArch32.TakeHypTrapException(0x03); else CP15ISB(); elsif PSTATE.EL == EL1 then if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T7 == '1' then AArch64.AArch32SystemAccessTrap(EL2, 0x03); elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T7 == '1' then AArch32.TakeHypTrapException(0x03); elsif SCTLR.CP15BEN == '0' then UNDEFINED; else CP15ISB(); elsif PSTATE.EL == EL2 then if HSCTLR.CP15BEN == '0' then UNDEFINED; else CP15ISB(); elsif PSTATE.EL == EL3 then if SCTLR.CP15BEN == '0' then UNDEFINED; else CP15ISB();

AArch32 Registers | AArch64 Registers | AArch32 Instructions | AArch64 Instructions | Index by Encoding | External Registers | External Registers by Offset | Registers by Functional Group | Proprietary Notice

26/03/2024 09:49; 67c0ae5282a7629ba0ea0ba7267b43cd4f7939f6

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