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HCPTR, Hyp Architectural Feature Trap Register

The HCPTR characteristics are:

Purpose

Controls:

  • Trapping to Hyp mode of Non-secure access, at EL1 or EL0, to trace, and to Advanced SIMD and floating-point functionality.
  • Hyp mode access to trace, and to Advanced SIMD and floating-point functionality.
Note

Accesses to this functionality:

  • From Non-secure modes other than Hyp mode are also affected by settings in the CPACR and NSACR.
  • From Hyp mode are also affected by settings in the NSACR.

Exceptions generated by the CPACR and NSACR controls are higher priority than those generated by the HCPTR controls.

Configuration

AArch32 System register HCPTR bits [31:0] are architecturally mapped to AArch64 System register CPTR_EL2[31:0] .

If EL2 is not implemented, this register is RES0 from EL3.

Some or all RW fields of this register have defined reset values. These apply only if the PE resets into EL2 with EL2 using AArch32, or into EL3 with EL3 using AArch32. Otherwise, RW fields in this register reset to architecturally UNKNOWN values.

Attributes

HCPTR is a 32-bit register.

Field descriptions

The HCPTR bit assignments are:

313029282726252423222120191817161514131211109876543210
TCPACTAMRES0TTARES0TASERES0RES1TCP11TCP10RES1

TCPAC, bit [31]

Traps Non-secure EL1 accesses to the CPACR to Hyp mode.

TCPACMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

Non-secure EL1 accesses to the CPACR are trapped to Hyp mode.

Note

The CPACR is not accessible at EL0.

In a system where the PE resets into EL2 or EL3, this field resets to 0.

TAM, bit [30]

When AMUv1 is implemented:

Trap Activity Monitor access. Traps Non-secure EL1 and EL0 accesses to all Activity Monitor registers to EL2.

TAMMeaning
0b0

Accesses from Non-secure EL1 and EL0 to Activity Monitor registers are not trapped.

0b1

Accesses from Non-secure EL1 and EL0 to Activity Monitor registers are trapped to Hyp mode.

In a system where the PE resets into EL2 or EL3, this field resets to 0.


Otherwise:

Reserved, RES0.

Bits [29:21]

Reserved, RES0.

TTA, bit [20]

Traps Non-secure System register accesses to all implemented trace registers to Hyp mode.

TTAMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

Any Non-secure System register access to an implemented trace register is trapped to Hyp mode, unless the access is trapped to EL1 by a CPACR or NSACR control, or the access is from Non-secure EL0 and the definition of the register in the appropriate trace architecture specification indicates that the register is not accessible from EL0. A trapped instruction generates:

  • A Hyp Trap exception, if the exception is taken from Non-secure EL0 or EL1.
  • An Undefined Instruction exception taken to Hyp mode, if the exception is taken from Hyp mode.

If the implementation does not include a PE trace unit, or does not include a System register interface to the PE trace unit registers, it is IMPLEMENTATION DEFINED whether this bit:

  • Is RES0.
  • Is RES1.
  • Can be written from Hyp mode, and from Secure Monitor mode when SCR.NS is 1.

If EL3 is implemented and is using AArch32, and the value of NSACR.NSTRCDIS is 1, in Non-secure state this field behaves as RAO/WI, regardless of its actual value.

Note
  • The ETMv4 architecture does not permit EL0 to access the trace registers. If the implementation includes an ETMv4 implementation, EL0 accesses to the trace registers are UNDEFINED, and a resulting Undefined Instruction exception is higher priority than a HCPTR.TTA Hyp Trap exception.
  • The architecture does not provide traps on trace register accesses through the optional memory-mapped debug 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.

In a system where the PE resets into EL2 or EL3, this field resets to 0.

Bits [19:16]

Reserved, RES0.

TASE, bit [15]

Traps Non-secure execution of Advanced SIMD instructions to Hyp mode when the value of HCPTR.TCP10 is 0.

TASEMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

When the value of HCPTR.TCP10 is 0, any attempt to execute an Advanced SIMD instruction in Non-secure state is trapped to Hyp mode, unless it is trapped to EL1 by a CPACR or NSACR control. A trapped instruction generates:

  • A Hyp Trap exception, if the exception is taken from Non-secure EL0 or EL1.
  • An Undefined Instruction exception taken to Hyp mode, if the exception is taken from Hyp mode.

When the value of HCPTR.TCP10 is 1, the value of this field is ignored.

If the implementation does not include Advanced SIMD and floating-point functionality, this field is RES1. Otherwise, it is IMPLEMENTATION DEFINED whether this field is implemented as a RW field. If it is not implemented as a RW field, then it is RAZ/WI.

If EL3 is implemented and is using AArch32, and the value of NSACR.NSASEDIS is 1, in Non-secure state this field behaves as RAO/WI, regardless of its actual value. This applies even if the field is implemented as RAZ/WI.

For the list of instructions affected by this field, see 'Controls of Advanced SIMD operation that do not apply to floating-point operation' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section E1.

In a system where the PE resets into EL2 or EL3, this field resets to 0.

Bit [14]

Reserved, RES0.

Bits [13:12]

Reserved, RES1.

TCP11, bit [11]

The value of this field is ignored. If this field is programmed with a different value to the TCP10 bit then this field is UNKNOWN on a direct read of the HCPTR.

If the implementation does not include Advanced SIMD and floating-point functionality, this field is RES1.

If EL3 is implemented and is using AArch32, and the value of NSACR.cp10 is 0, in Non-secure state this field behaves as RAO/WI, regardless of its actual value.

In a system where the PE resets into EL2 or EL3, this field resets to 0.

TCP10, bit [10]

Trap Non-secure accesses to Advanced SIMD and floating-point functionality to Hyp mode:

TCP10Meaning
0b0

This control does not cause any instructions to be trapped.

0b1

Any attempted access to Advanced SIMD and floating-point functionality from Non-secure state is trapped to Hyp mode, unless it is trapped to EL1 by a CPACR or NSACR control. A trapped instruction generates:

  • A Hyp Trap exception, if the exception is taken from Non-secure EL0 or EL1.
  • An Undefined Instruction exception taken to Hyp mode, if the exception is taken from Hyp mode.

The Advanced SIMD and floating-point features controlled by these fields are:

  • Execution of any floating-point or Advanced SIMD instruction.
  • Any access to the Advanced SIMD and floating-point registers D0-D31 and their views as S0-S31 and Q0-Q15.
  • Any access to the FPSCR, FPSID, MVFR0, MVFR1, MVFR2, or FPEXC System registers.

If the implementation does not include Advanced SIMD and floating-point functionality, this field is RES1.

If EL3 is implemented and is using AArch32, and the value of NSACR.cp10 is 0, in Non-secure state this field behaves as RAO/WI, regardless of its actual value.

In a system where the PE resets into EL2 or EL3, this field resets to 0.

Bits [9:0]

Reserved, RES1.

Accessing the HCPTR

Accesses to this register use the following encodings:

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

coprocopc1CRnCRmopc2
0b11110b1000b00010b00010b010
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T1 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T1 == '1' then
        AArch32.TakeHypTrapException(0x03);
    else
        UNDEFINED;
elsif PSTATE.EL == EL2 then
    if HaveEL(EL3) && !ELUsingAArch32(EL3) && CPTR_EL3.TCPAC == '1' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x03);
    else
        return HCPTR;
elsif PSTATE.EL == EL3 then
    if SCR.NS == '0' then
        UNDEFINED;
    else
        return HCPTR;
              

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

coprocopc1CRnCRmopc2
0b11110b1000b00010b00010b010
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T1 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T1 == '1' then
        AArch32.TakeHypTrapException(0x03);
    else
        UNDEFINED;
elsif PSTATE.EL == EL2 then
    if HaveEL(EL3) && !ELUsingAArch32(EL3) && CPTR_EL3.TCPAC == '1' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x03);
    else
        HCPTR = R[t];
elsif PSTATE.EL == EL3 then
    if SCR.NS == '0' then
        UNDEFINED;
    else
        HCPTR = R[t];
              


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