CPACR_EL1 | Jon's Arm Reference

Controls access to trace, SME, Streaming SVE, SVE, and Advanced SIMD and floating-point functionality.

Configuration

AArch64 System register CPACR_EL1 bits [31:0] are architecturally mapped to AArch32 System register CPACR[31:0].

When EL2 is implemented and enabled in the current Security state and the Effective value of HCR_EL2.{E2H, TGE} == {1, 1}, the fields in this register have no effect on execution at EL0 and EL1. In this case, the controls provided by CPTR_EL2 are used.

Attributes

Field descriptions

Bits [63:30]

E0POE, bit [29]

When FEAT_S1POE is implemented:

E0POE	Meaning
0b0	This control causes EL0 access to POR_EL0 to be trapped.
0b1	This control does not cause any instructions to be trapped.

Otherwise:

TTA, bit [28]

Traps EL0 and EL1 System register accesses to all implemented trace registers from both Execution states to EL1, or to EL2 when it is implemented and enabled in the current Security state and HCR_EL2.TGE is 1, as follows:

In AArch64 state, accesses to trace registers are trapped, reported using ESR_ELx.EC value 0x18.
In AArch32 state, MRC and MCR accesses to trace registers are trapped, reported using ESR_ELx.EC value 0x05.
In AArch32 state, MRRC and MCRR accesses to trace registers are trapped, reported using ESR_ELx.EC value 0x0C.

TTA	Meaning
0b0	This control does not cause any instructions to be trapped.
0b1	This control causes EL0 and EL1 System register accesses to all implemented trace registers to be trapped.

Note

The ETMv4 architecture and ETE do not permit EL0 to access the trace registers. If the trace unit implements FEAT_ETMv4 or FEAT_ETE, EL0 accesses to the trace registers are UNDEFINED, and any resulting exception is higher priority than an exception that would be generated because the value of CPACR_EL1.TTA is 1.
The Arm architecture does not provide traps on trace register accesses through the optional memory-mapped interface.

System register accesses to the trace registers can have side-effects. When a System register access is trapped, any side-effects that are normally associated with the access do not occur before the exception is taken.

If System register access to the trace functionality is not implemented, this bit is RES0.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

Bits [27:26]

SMEN, bits [25:24]

When FEAT_SME is implemented:

Traps execution at EL1 and EL0 of SME instructions, SVE instructions when FEAT_SVE is not implemented or the PE is in Streaming SVE mode, and instructions that directly access the SVCR or SMCR_EL1 System registers to EL1, or to EL2 when EL2 is implemented and enabled in the current Security state and HCR_EL2.TGE is 1.

When instructions that directly access the SVCR System register are trapped with reference to this control, the MSR SVCRSM, MSR SVCRZA, and MSR SVCRSMZA instructions are also trapped.

The exception is reported using ESR_ELx.EC value of 0x1D, with an ISS code of 0x0000000.

This field does not affect whether Streaming SVE or SME register values are valid.

A trap taken as a result of CPACR_EL1.SMEN has precedence over a trap taken as a result of CPACR_EL1.FPEN.

SMEN	Meaning
0b00	This control causes execution of these instructions at EL1 and EL0 to be trapped.
0b01	This control causes execution of these instructions at EL0 to be trapped, but does not cause execution of any instructions at EL1 to be trapped.
0b10	This control causes execution of these instructions at EL1 and EL0 to be trapped.
0b11	This control does not cause execution of any instructions to be trapped.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

Otherwise:

Bits [23:22]

FPEN, bits [21:20]

Traps execution at EL1 and EL0 of instructions that access the Advanced SIMD and floating-point registers from both Execution states to EL1, reported using ESR_ELx.EC value 0x07, or to EL2 reported using ESR_ELx.EC value 0x00 when EL2 is implemented and enabled in the current Security state and HCR_EL2.TGE is 1, as follows:

In AArch64 state, accesses to FPMR, FPCR, FPSR, any of the SIMD and floating-point registers V0-V31, including their views as D0-D31 registers or S0-31 registers.
In AArch32 state, FPSCR, and any of the SIMD and floating-point registers Q0-15, including their views as D0-D31 registers or S0-31 registers.

Traps execution at EL1 and EL0 of SME and SVE instructions to EL1, or to EL2 when EL2 is implemented and enabled for the current Security state and HCR_EL2.TGE is 1. The exception is reported using ESR_ELx.EC value 0x07.

A trap taken as a result of CPACR_EL1.SMEN has precedence over a trap taken as a result of CPACR_EL1.FPEN.

A trap taken as a result of CPACR_EL1.ZEN has precedence over a trap taken as a result of CPACR_EL1.FPEN.

FPEN	Meaning
0b00	This control causes execution of these instructions at EL1 and EL0 to be trapped.
0b01	This control causes execution of these instructions at EL0 to be trapped, but does not cause execution of any instructions at EL1 to be trapped.
0b10	This control causes execution of these instructions at EL1 and EL0 to be trapped.
0b11	This control does not cause execution of any instructions to be trapped.

Writes to MVFR0, MVFR1, and MVFR2 from EL1 or higher are CONSTRAINED UNPREDICTABLE and whether these accesses can be trapped by this control depends on implemented CONSTRAINED UNPREDICTABLE behavior.

Note

Attempts to write to the FPSID count as use of the registers for accesses from EL1 or higher.
Accesses from EL0 to FPSID, MVFR0, MVFR1, MVFR2, and FPEXC are UNDEFINED, and any resulting exception is higher priority than an exception that would be generated because the value of CPACR_EL1.FPEN is not 0b11.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

Bits [19:18]

ZEN, bits [17:16]

When FEAT_SVE is implemented:

Traps execution at EL1 and EL0 of SVE instructions when the PE is not in Streaming SVE mode, and instructions that directly access the ZCR_EL1 System register to EL1, or to EL2 when EL2 is implemented and enabled in the current Security state and HCR_EL2.TGE is 1.

The exception is reported using ESR_ELx.EC value 0x19.

A trap taken as a result of CPACR_EL1.ZEN has precedence over a trap taken as a result of CPACR_EL1.FPEN.

ZEN	Meaning
0b00	This control causes execution of these instructions at EL1 and EL0 to be trapped.
0b01	This control causes execution of these instructions at EL0 to be trapped, but does not cause execution of any instructions at EL1 to be trapped.
0b10	This control causes execution of these instructions at EL1 and EL0 to be trapped.
0b11	This control does not cause execution of any instructions to be trapped.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

Otherwise:

Bits [15:0]

Accessing CPACR_EL1

When the Effective value of HCR_EL2.E2H is 1, without explicit synchronization, access from EL3 using the mnemonic CPACR_EL1 or CPACR_EL12 are not guaranteed to be ordered with respect to accesses using the other mnemonic.

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

MRS <Xt>, CPACR_EL1

op0	op1	CRn	CRm	op2
0b11	0b000	0b0001	0b0000	0b010

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if HaveEL(EL3) && EL3SDDUndefPriority() && CPTR_EL3.TCPAC == '1' then UNDEFINED; elsif EL2Enabled() && CPTR_EL2.TCPAC == '1' then AArch64.SystemAccessTrap(EL2, 0x18); elsif EL2Enabled() && IsFeatureImplemented(FEAT_FGT) && (!HaveEL(EL3) || SCR_EL3.FGTEn == '1') && HFGRTR_EL2.CPACR_EL1 == '1' then AArch64.SystemAccessTrap(EL2, 0x18); elsif HaveEL(EL3) && CPTR_EL3.TCPAC == '1' then if EL3SDDUndef() then UNDEFINED; else AArch64.SystemAccessTrap(EL3, 0x18); elsif EffectiveHCR_EL2_NVx() == '111' then X[t, 64] = NVMem[0x100]; else X[t, 64] = CPACR_EL1; elsif PSTATE.EL == EL2 then if HaveEL(EL3) && EL3SDDUndefPriority() && CPTR_EL3.TCPAC == '1' then UNDEFINED; elsif HaveEL(EL3) && CPTR_EL3.TCPAC == '1' then if EL3SDDUndef() then UNDEFINED; else AArch64.SystemAccessTrap(EL3, 0x18); elsif ELIsInHost(EL2) then X[t, 64] = CPTR_EL2; else X[t, 64] = CPACR_EL1; elsif PSTATE.EL == EL3 then X[t, 64] = CPACR_EL1;

MSR CPACR_EL1, <Xt>

op0	op1	CRn	CRm	op2
0b11	0b000	0b0001	0b0000	0b010

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if HaveEL(EL3) && EL3SDDUndefPriority() && CPTR_EL3.TCPAC == '1' then UNDEFINED; elsif EL2Enabled() && CPTR_EL2.TCPAC == '1' then AArch64.SystemAccessTrap(EL2, 0x18); elsif EL2Enabled() && IsFeatureImplemented(FEAT_FGT) && (!HaveEL(EL3) || SCR_EL3.FGTEn == '1') && HFGWTR_EL2.CPACR_EL1 == '1' then AArch64.SystemAccessTrap(EL2, 0x18); elsif HaveEL(EL3) && CPTR_EL3.TCPAC == '1' then if EL3SDDUndef() then UNDEFINED; else AArch64.SystemAccessTrap(EL3, 0x18); elsif EffectiveHCR_EL2_NVx() == '111' then NVMem[0x100] = X[t, 64]; else CPACR_EL1 = X[t, 64]; elsif PSTATE.EL == EL2 then if HaveEL(EL3) && EL3SDDUndefPriority() && CPTR_EL3.TCPAC == '1' then UNDEFINED; elsif HaveEL(EL3) && CPTR_EL3.TCPAC == '1' then if EL3SDDUndef() then UNDEFINED; else AArch64.SystemAccessTrap(EL3, 0x18); elsif ELIsInHost(EL2) then CPTR_EL2 = X[t, 64]; else CPACR_EL1 = X[t, 64]; elsif PSTATE.EL == EL3 then CPACR_EL1 = X[t, 64];

MRS <Xt>, CPACR_EL12

op0	op1	CRn	CRm	op2
0b11	0b101	0b0001	0b0000	0b010

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EffectiveHCR_EL2_NVx() == '101' then X[t, 64] = NVMem[0x100]; elsif EffectiveHCR_EL2_NVx() IN {'xx1'} then AArch64.SystemAccessTrap(EL2, 0x18); else UNDEFINED; elsif PSTATE.EL == EL2 then if ELIsInHost(EL2) then if HaveEL(EL3) && EL3SDDUndefPriority() && CPTR_EL3.TCPAC == '1' then UNDEFINED; elsif HaveEL(EL3) && CPTR_EL3.TCPAC == '1' then if EL3SDDUndef() then UNDEFINED; else AArch64.SystemAccessTrap(EL3, 0x18); else X[t, 64] = CPACR_EL1; else UNDEFINED; elsif PSTATE.EL == EL3 then if ELIsInHost(EL2) then X[t, 64] = CPACR_EL1; else UNDEFINED;

MSR CPACR_EL12, <Xt>

op0	op1	CRn	CRm	op2
0b11	0b101	0b0001	0b0000	0b010

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EffectiveHCR_EL2_NVx() == '101' then NVMem[0x100] = X[t, 64]; elsif EffectiveHCR_EL2_NVx() IN {'xx1'} then AArch64.SystemAccessTrap(EL2, 0x18); else UNDEFINED; elsif PSTATE.EL == EL2 then if ELIsInHost(EL2) then if HaveEL(EL3) && EL3SDDUndefPriority() && CPTR_EL3.TCPAC == '1' then UNDEFINED; elsif HaveEL(EL3) && CPTR_EL3.TCPAC == '1' then if EL3SDDUndef() then UNDEFINED; else AArch64.SystemAccessTrap(EL3, 0x18); else CPACR_EL1 = X[t, 64]; else UNDEFINED; elsif PSTATE.EL == EL3 then if ELIsInHost(EL2) then CPACR_EL1 = X[t, 64]; else UNDEFINED;

CPACR_EL1: Architectural Feature Access Control Register

Purpose

Configuration

Attributes

Field descriptions

Bits [63:30]

E0POE, bit [29]

When FEAT_S1POE is implemented:

Otherwise:

TTA, bit [28]

Bits [27:26]

SMEN, bits [25:24]

When FEAT_SME is implemented:

Otherwise:

Bits [23:22]

FPEN, bits [21:20]

Bits [19:18]

ZEN, bits [17:16]

When FEAT_SVE is implemented:

Otherwise:

Bits [15:0]

Accessing CPACR_EL1

63	62	61	60	59	58	57	56	55	54	53	52	51	50	49	48	47	46	45	44	43	42	41	40	39	38	37	36	35	34	33	32
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
RES0
RES0		E0POE	TTA	RES0		SMEN		RES0		FPEN		RES0		ZEN		RES0

CPACR_EL1: Architectural Feature Access Control Register

Purpose

Configuration

Attributes

Field descriptions

Bits [63:30]

E0POE, bit [29]When FEAT_S1POE is implemented:

Otherwise:

TTA, bit [28]

Bits [27:26]

SMEN, bits [25:24]When FEAT_SME is implemented:

Otherwise:

Bits [23:22]

FPEN, bits [21:20]

Bits [19:18]

ZEN, bits [17:16]When FEAT_SVE is implemented:

Otherwise:

Bits [15:0]

Accessing CPACR_EL1

E0POE, bit [29]

When FEAT_S1POE is implemented:

SMEN, bits [25:24]

When FEAT_SME is implemented:

ZEN, bits [17:16]

When FEAT_SVE is implemented: