The SCTLR_EL1 characteristics are:
Provides top level control of the system, including its memory system, at EL1 and EL0.
This register is part of the Other system control registers functional group.
AArch64 System register SCTLR_EL1 is architecturally mapped to AArch32 System register SCTLR.
Some or all RW fields of this register have defined reset values. These apply only if the PE resets into EL1 using AArch64. Otherwise, RW fields in this register reset to architecturally UNKNOWN values.
SCTLR_EL1 is a 32-bit register.
The SCTLR_EL1 bit assignments are:
31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
0 | 0 | LSMAOE | nTLSMD | 0 | UCI | EE | E0E | SPAN | 1 | IESB | 1 | WXN | nTWE | 0 | nTWI | UCT | DZE | 0 | I | 1 | 0 | UMA | SED | ITD | 0 | CP15BEN | SA0 | SA | C | A | M |
Reserved, RES0.
Load Multiple and Store Multiple Atomicity and Ordering Enable. When the OPTIONAL feature ARMv8.2-LSMAOC is implemented, defined values are:
LSMAOE | Meaning |
---|---|
0 |
For all memory accesses at EL0, A32 and T32 Load Multiple and Store Multiple can have an interrupt taken during the sequence memory accesses, and the memory accesses are not required to be ordered. |
1 |
The ordering and interrupt behavior of A32 and T32 Load Multiple and Store Multiple at EL0 is as defined for ARMv8.0. |
This bit is permitted to be cached in a TLB.
If this bit is not implemented, it is RES1.
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1,1}, this bit has no effect on execution at EL0.
Reserved, RES1.
No Trap Load Multiple and Store Multiple to Device-nGRE/Device-nGnRE/Device-nGnRnE memory. When the OPTIONAL feature ARMv8.2-LSMAOC is implemented, defined values are:
nTLSMD | Meaning |
---|---|
0 |
All memory accesses by A32 and T32 Load Multiple and Store Multiple at EL0 that are marked at stage 1 as Device-nGRE/Device-nGnRE/Device-nGnRnE memory are trapped and generate a stage 1 Alignment fault. |
1 |
All memory accesses by A32 and T32 Load Multiple and Store Multiple at EL0 that are marked at stage 1 as Device-nGRE/Device-nGnRE/Device-nGnRnE memory are not trapped. |
This bit is permitted to be cached in a TLB.
If this bit is not implemented, it is RES1.
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1,1}, this bit has no effect on execution at EL0.
Reserved, RES1.
Reserved, RES0.
Traps EL0 execution of cache maintenance instructions to EL1, from AArch64 state only.
UCI | Meaning |
---|---|
0 |
Any attempt to execute a DC CVAU, DC CIVAC, DC CVAC, DC CVAP, or IC IVAU instruction at EL0 using AArch64 is trapped to EL1. |
1 |
This control does not cause any instructions to be trapped. |
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on execution at EL0.
When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.
Endianness of data accesses at EL1, and stage 1 translation table walks in the EL1&0 translation regime.
The possible values of this bit are:
EE | Meaning |
---|---|
0 |
Explicit data accesses at EL1, and stage 1 translation table walks in the EL1&0 translation regime are little-endian. |
1 |
Explicit data accesses at EL1, and stage 1 translation table walks in the EL1&0 translation regime are big-endian. |
If an implementation does not provide Big-endian support at Exception Levels higher than EL0, this bit is RES0.
If an implementation does not provide Little-endian support at Exception Levels higher than EL0, this bit is RES1.
The EE bit is permitted to be cached in a TLB.
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on the PE.
When this register has an architecturally-defined reset value, if this field is implemented as an RW field, it resets to an IMPLEMENTATION DEFINED value.
Endianness of data accesses at EL0.
The possible values of this bit are:
E0E | Meaning |
---|---|
0 |
Explicit data accesses at EL0 are little-endian. |
1 |
Explicit data accesses at EL0 are big-endian. |
If an implementation only supports Little-endian accesses at EL0 then this bit is RES0. This option is not permitted when SCTLR_EL1.EE is RES1.
If an implementation only supports Big-endian accesses at EL0 then this bit is RES1. This option is not permitted when SCTLR_EL1.EE is RES0.
This bit has no effect on the endianness of LDTR, LDTRH, LDTRSH, LDTRSW, STTR, and STTRH instructions executed at EL1.
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on execution at EL0.
When this register has an architecturally-defined reset value, if this field is implemented as an RW field, it resets to a value that is architecturally UNKNOWN.
Set Privileged Access Never, on taking an exception to EL1.
SPAN | Meaning |
---|---|
0 |
PSTATE.PAN is set to 1 on taking an exception to EL1. |
1 |
The value of PSTATE.PAN is left unchanged on taking an exception to EL1. |
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on execution at EL0.
When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.
Reserved, RES1.
Reserved, RES1.
Implicit Error Synchronizaition Barrier enable. Permitted values are:
IESB | Meaning |
---|---|
0 |
Disabled. |
1 |
An implicit ErrorSynchronizationBarrier() call is added:
|
When the PE is in Debug state, the effect of this field is CONSTRAINED UNPREDICTABLE, and regardless of the value of the field its effective value might be 0 or 1. If the effective value of the field is 1, then an implicit ErrorSynchronizationBarrier() is added after each DCPSx instruction and before each DRPS instruction, in addition to the other cases where it is added.
This field is part of the required ARMv8.2 implementation of the RAS Extension. See 'The Reliability, Availability, and Serviceability (RAS) Extension' in the ARMv8 ARM, chapter A1 'Introduction to the ARMv8 Architecture'.
When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.
Reserved, RES0.
Reserved, RES1.
Write permission implies XN (Execute-never). For the EL1&0 translation regime, this bit can force all memory regions that are writable to be treated as XN. The possible values of this bit are:
WXN | Meaning |
---|---|
0 |
This control has no effect on memory access permissions. |
1 |
Any region that is writable in the EL1&0 translation regime is forced to XN for accesses from software executing at EL1 or EL0. |
The WXN bit is permitted to be cached in a TLB.
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on the PE.
When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.
Traps EL0 execution of WFE instructions to EL1, from both Execution states.
nTWE | Meaning |
---|---|
0 |
Any attempt to execute a WFE instruction at EL0 is trapped to EL1, if the instruction would otherwise have caused the PE to enter a low-power state. |
1 |
This control does not cause any instructions to be trapped. |
In AArch32 state, the attempted execution of a conditional WFE instruction is only trapped if the instruction passes its condition code check.
Since a WFE or WFI can complete at any time, even without a Wakeup event, the traps on WFE of WFI are not guaranteed to be taken, even if the WFE or WFI is executed when there is no Wakeup event. The only guarantee is that if the instruction does not complete in finite time in the absence of a Wakeup event, the trap will be taken.
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on execution at EL0.
When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.
Reserved, RES0.
Traps EL0 execution of WFI instructions to EL1, from both Execution states.
nTWI | Meaning |
---|---|
0 |
Any attempt to execute a WFI instruction at EL0 is trapped EL1, if the instruction would otherwise have caused the PE to enter a low-power state. |
1 |
This control does not cause any instructions to be trapped. |
In AArch32 state, the attempted execution of a conditional WFI instruction is only trapped if the instruction passes its condition code check.
Since a WFE or WFI can complete at any time, even without a Wakeup event, the traps on WFE of WFI are not guaranteed to be taken, even if the WFE or WFI is executed when there is no Wakeup event. The only guarantee is that if the instruction does not complete in finite time in the absence of a Wakeup event, the trap will be taken.
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on execution at EL0.
When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.
Traps EL0 accesses to the CTR_EL0 to EL1, from AArch64 state only.
UCT | Meaning |
---|---|
0 |
Accesses to the CTR_EL0 from EL0 using AArch64 are trapped to EL1. |
1 |
This control does not cause any instructions to be trapped. |
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on execution at EL0.
When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.
Traps EL0 execution of DC ZVA instructions to EL1, from AArch64 state only.
DZE | Meaning |
---|---|
0 |
Any attempt to execute a DC ZVA instruction at EL0 using AArch64 is trapped to EL1. Reading DCZID_EL0.DZP from EL0 returns 1, indicating that DC ZVA instructions are not supported. |
1 |
This control does not cause any instructions to be trapped. |
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on execution at EL0.
When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.
Reserved, RES0.
Instruction access Cacheability control, for accesses at EL0 and EL1:
I | Meaning |
---|---|
0 |
All instruction access to Normal memory from EL0 and EL1 are Non-cacheable for all levels of instruction and unified cache. If the value of SCTLR_EL1.M is 0, instruction accesses from stage 1 of the EL1&0 translation regime are to Normal, Outer Shareable, Inner Non-cacheable, Outer Non-cacheable memory. |
1 |
This control has no effect on the Cacheability of instruction access to Normal memory from EL0 and EL1. If the value of SCTLR_EL1.M is 0, instruction accesses from stage 1 of the EL1&0 translation regime are to Normal, Outer Shareable, Inner Write-Through, Outer Write-Through memory. |
When the value of the HCR_EL2.DC bit is 1, then instruction access to Normal memory from EL0 and EL1 are Cacheable regardless of the value of the SCTLR_EL1.I bit.
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on the PE.
When this register has an architecturally-defined reset value, this field resets to 0.
Reserved, RES1.
Reserved, RES0.
User Mask Access. Traps EL0 execution of MSR and MRS instructions that access the PSTATE.{D, A, I, F} masks to EL1, from AArch64 state only.
UMA | Meaning |
---|---|
0 |
Any attempt at EL0 using AArch64 to execute an MRS, MSR(register), or MSR(immediate) instruction that accesses the DAIF is trapped to EL1. |
1 |
This control does not cause any instructions to be trapped. |
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on execution at EL0.
When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.
SETEND instruction disable. Disables SETEND instructions at EL0 using AArch32.
SED | Meaning |
---|---|
0 |
SETEND instruction execution is enabled at EL0 using AArch32. |
1 |
SETEND instructions are UNDEFINED at EL0 using AArch32. |
If the implementation does not support mixed-endian operation at any Exception level, this bit is RES1.
If EL0 cannot use AArch32, this bit is RES1.
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on execution at EL0.
When this register has an architecturally-defined reset value, if this field is implemented as an RW field, it resets to a value that is architecturally UNKNOWN.
IT Disable. Disables some uses of IT instructions at EL0 using AArch32.
ITD | Meaning |
---|---|
0 |
All IT instruction functionality is enabled at EL0 using AArch32. |
1 |
Any attempt at EL0 using AArch32 to execute any of the following is UNDEFINED:
These instructions are always UNDEFINED, regardless of whether they would pass or fail the condition code check that applies to them as a result of being in an IT block. It is IMPLEMENTATION DEFINED whether the IT instruction is treated as:
This means that, for the situations that are UNDEFINED, either the second 16-bit instruction or the 32-bit instruction is UNDEFINED. An implementation might vary dynamically as to whether IT is treated as a 16-bit instruction or the first half of a 32-bit instruction. |
If an instruction in an active IT block that would be disabled by this field sets this field to 1 then behavior is CONSTRAINED UNPREDICTABLE. For more information see 'Changes to an ITD control by an instruction in an IT block' in the ARMv8 ARM, section E1.2.4
If EL0 cannot use AArch32, this bit is RES1.
ITD is optional, but if it is implemented in the SCTLR then it must also be implemented in the SCTLR_EL1. If it is not implemented then this bit is RAZ/WI.
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on execution at EL0.
When this register has an architecturally-defined reset value, if this field is implemented as an RW field, it resets to a value that is architecturally UNKNOWN.
Reserved, RES0.
System instruction memory barrier enable. Enables accesses to the DMB, DSB, and ISB System instructions in the (coproc==1111) encoding space from EL0:
CP15BEN | Meaning |
---|---|
0 |
EL0 using AArch32: EL0 execution of the CP15DMB, CP15DSB, and CP15ISB instructions is UNDEFINED. |
1 |
EL0 using AArch32: EL0 execution of the CP15DMB, CP15DSB, and CP15ISB instructions is enabled. |
If EL0 cannot use AArch32, this bit is RES0.
CP15BEN is optional, but if it is implemented in the SCTLR then it must also be implemented in the SCTLR_EL1. If it is not implemented then this bit is RAO/WI.
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on execution at EL0.
When this register has an architecturally-defined reset value, if this field is implemented as an RW field, it resets to a value that is architecturally UNKNOWN.
SP Alignment check enable for EL0. When set to 1, if a load or store instruction executed at EL0 uses the SP as the base address and the SP is not aligned to a 16-byte boundary, then a SP alignment fault exception is generated. For more information, see 'SP alignment checking' in the ARMv8 ARM, section D1 (The AArch64 System Level Programmers' Model).
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on execution at EL0.
When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.
SP Alignment check enable. When set to 1, if a load or store instruction executed at EL1 uses the SP as the base address and the SP is not aligned to a 16-byte boundary, then a SP alignment fault exception is generated. For more information, see 'SP alignment checking' in the ARMv8 ARM, section D1 (The AArch64 System Level Programmers' Model).
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on the PE.
When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.
Cacheability control, for data accesses.
C | Meaning |
---|---|
0 |
All data access to Normal memory from EL0 and EL1, and all Normal memory accesses to the EL1&0 stage 1 translation tables, are Non-cacheable for all levels of data and unified cache. |
1 |
This control has no effect on the Cacheability of:
|
When the value of the HCR_EL2.DC bit is 1, the PE ignores SCLTR.C. This means that Non-secure EL0 and Non-secure EL1 data accesses to Normal memory are Cacheable.
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on the PE.
When this register has an architecturally-defined reset value, this field resets to 0.
Alignment check enable. This is the enable bit for Alignment fault checking at EL1 and EL0:
A | Meaning |
---|---|
0 |
Alignment fault checking disabled when executing at EL1 or EL0. Instructions that load or store one or more registers, other than load/store exclusive and load-acquire/store-release, do not check that the address being accessed is aligned to the size of the data element(s) being accessed. |
1 |
Alignment fault checking enabled when executing at EL1 or EL0. All instructions that load or store one or more registers have an alignment check that the address being accessed is aligned to the size of the data element(s) being accessed. If this check fails it causes an Alignment fault, which is taken as a Data Abort exception. |
Load/store exclusive and load-acquire/store-release instructions have an alignment check regardless of the value of the A bit.
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on execution at EL0.
When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.
MMU enable for EL1 and EL0 stage 1 address translation. Possible values of this bit are:
M | Meaning |
---|---|
0 |
EL1 and EL0 stage 1 address translation disabled. See the SCTLR_EL1.I field for the behavior of instruction accesses to Normal memory. |
1 |
EL1 and EL0 stage 1 address translation enabled. |
If the value of HCR_EL2.{DC, TGE} is not {0, 0} then in Non-secure state the PE behaves as if the value of the SCTLR_EL1.M field is 0 for all purposes other than returning the value of a direct read of the field.
When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this bit has no effect on the PE.
When this register has an architecturally-defined reset value, this field resets to 0.
This register can be read using MRS with the following syntax:
MRS <Xt>, <systemreg>
This register can be written using MSR (register) with the following syntax:
MSR <systemreg>, <Xt>
This syntax uses the following encoding in the System instruction encoding space:
<systemreg> | op0 | op1 | CRn | CRm | op2 |
---|---|---|---|---|---|
SCTLR_EL1 | 11 | 000 | 0001 | 0000 | 000 |
SCTLR_EL12 | 11 | 101 | 0001 | 0000 | 000 |
The register is accessible as follows:
<systemreg> | Control | Accessibility | |||||
---|---|---|---|---|---|---|---|
E2H | TGE | NS | EL0 | EL1 | EL2 | EL3 | |
SCTLR_EL1 | x | x | 0 | - | RW | n/a | RW |
SCTLR_EL1 | 0 | 0 | 1 | - | RW | RW | RW |
SCTLR_EL1 | 0 | 1 | 1 | - | n/a | RW | RW |
SCTLR_EL1 | 1 | 0 | 1 | - | RW | SCTLR_EL2 | RW |
SCTLR_EL1 | 1 | 1 | 1 | - | n/a | SCTLR_EL2 | RW |
SCTLR_EL12 | x | x | 0 | - | - | n/a | - |
SCTLR_EL12 | 0 | 0 | 1 | - | - | - | - |
SCTLR_EL12 | 0 | 1 | 1 | - | n/a | - | - |
SCTLR_EL12 | 1 | 0 | 1 | - | - | RW | RW |
SCTLR_EL12 | 1 | 1 | 1 | - | n/a | RW | RW |
When HCR_EL2.E2H is 1, without explicit synchronization, access from EL3 using the mnemonic SCTLR_EL1 or SCTLR_EL12 are not guaranteed to be ordered with respect to accesses using the other mnemonic.
For a description of the prioritization of any generated exceptions, see section D1.13.2 (Synchronous exception prioritization) in the ARM® Architecture Reference Manual, ARMv8, for ARMv8-A architecture profile. Subject to the prioritization rules, the following traps and enables are applicable when accessing this register.
When EL2 is implemented and is using AArch64 and SCR_EL3.NS==1 && HCR_EL2.E2H==0 :
If HCR_EL2.TRVM==1, Non-secure read accesses to this register from EL1 are trapped to EL2.
If HCR_EL2.TVM==1, Non-secure write accesses to this register from EL1 are trapped to EL2.
When EL2 is implemented and is using AArch64 and SCR_EL3.NS==1 && HCR_EL2.E2H==1 && HCR_EL2.TGE==0 :
02/05/2017 15:43
Copyright © 2010-2017 ARM Limited or its affiliates. All rights reserved. This document is Non-Confidential.