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ID_PFR1_EL1, AArch32 Processor Feature Register 1

The ID_PFR1_EL1 characteristics are:

Purpose

Gives information about the AArch32 programmers' model.

Must be interpreted with ID_PFR0_EL1.

For general information about the interpretation of the ID registers see 'Principles of the ID scheme for fields in ID registers' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section D10.4.1.

Configuration

AArch64 System register ID_PFR1_EL1 bits [31:0] are architecturally mapped to AArch32 System register ID_PFR1[31:0] .

In an implementation that supports only AArch64 state, this register is UNKNOWN.

Attributes

ID_PFR1_EL1 is a 64-bit register.

Field descriptions

The ID_PFR1_EL1 bit assignments are:

6362616059585756555453525150494847464544434241403938373635343332
RES0
GICVirt_fracSec_fracGenTimerVirtualizationMProgModSecurityProgMod
313029282726252423222120191817161514131211109876543210

Bits [63:32]

Reserved, RES0.

GIC, bits [31:28]

System register GIC CPU interface. Defined values are:

GICMeaning
0b0000

No System register interface to the GIC CPU interface is supported.

0b0001

System register interface to versions 3.0 and 4.0 of the GIC CPU interface is supported.

All other values are reserved.

Virt_frac, bits [27:24]

Virtualization fractional field. When the Virtualization field is 0b0000, determines the support for features from the ARMv7 Virtualization Extensions. Defined values are:

Virt_fracMeaning
0b0000

No features from the ARMv7 Virtualization Extensions are implemented.

0b0001

The following features of the ARMv7 Virtualization Extensions are implemented:

  • The SCR.SIF bit, if EL3 is implemented.
  • The modifications to the SCR.AW and SCR.FW bits described in the Virtualization Extensions, if EL3 is implemented.
  • The MSR (banked register) and MRS (banked register) instructions.
  • The ERET instruction.

All other values are reserved.

In Armv8-A the permitted values are:

  • 0b0000 when EL2 is implemented.
  • 0b0001 when EL2 is not implemented.

This field is only valid when the value of ID_PFR1_EL1.Virtualization is 0, otherwise it holds the value 0b0000.

Note

The ID_ISAR registers do not identify whether the instructions added by the ARMv7 Virtualization Extensions are implemented.

Sec_frac, bits [23:20]

Security fractional field. When the Security field is 0b0000, determines the support for features from the ARMv7 Security Extensions. Defined values are:

Sec_fracMeaning
0b0000

No features from the ARMv7 Security Extensions are implemented.

0b0001

The following features from the ARMv7 Security Extensions are implemented:

  • The VBAR register.
  • The TTBCR.PD0 and TTBCR.PD1 bits.
0b0010

As for 0b0001, plus the ability to access Secure or Non-secure physical memory is supported.

All other values are reserved.

In Armv8-A the permitted values are:

  • 0b0000 when EL3 is implemented.
  • 0b0001 or 0b0010 when EL3 is not implemented.

This field is only valid when the value of ID_PFR1_EL1.Security is 0, otherwise it holds the value 0b0000.

GenTimer, bits [19:16]

Generic Timer support. Defined values are:

GenTimerMeaning
0b0000

Not implemented.

0b0001

Generic Timer implemented.

All other values are reserved.

In Armv8-A the only permitted value is 0b0001.

Virtualization, bits [15:12]

Virtualization support. Defined values are:

VirtualizationMeaning
0b0000

EL2, Hyp mode, and the HVC instruction not implemented.

0b0001

EL2, Hyp mode, the HVC instruction, and all the features described by Virt_frac == 0b0001 implemented.

All other values are reserved.

In Armv8-A the permitted values are:

  • 0b0000 when EL2 is not implemented.
  • 0b0001 when EL2 is implemented.

In an implementation that includes EL2, if EL2 cannot use AArch32 but EL1 can use AArch32 then this field has the value 0b0001.

If EL1 cannot use AArch32 then this field has the value 0b0000.

Note

The ID_ISARs do not identify whether the HVC instruction is implemented.

MProgMod, bits [11:8]

M profile programmers' model support. Defined values are:

MProgModMeaning
0b0000

Not supported.

0b0010

Support for two-stack programmers' model.

All other values are reserved.

In Armv8-A the only permitted value is 0b0000.

Security, bits [7:4]

Security support. Defined values are:

SecurityMeaning
0b0000

EL3, Monitor mode, and the SMC instruction not implemented.

0b0001

EL3, Monitor mode, the SMC instruction, and all the features described by Sec_frac == 0b0001 implemented.

0b0010

As for 0b0001, and adds the ability to set the NSACR.RFR bit. Not permitted in Armv8 as the NSACR.RFR bit is RES0.

All other values are reserved.

In Armv8-A the permitted values are:

  • 0b0000 when EL3 is not implemented.
  • 0b0001 when EL3 is implemented.

In an implementation that includes EL3, if EL3 cannot use AArch32 but EL1 can use AArch32 then this field has the value 0b0001.

If EL1 cannot use AArch32 then this field has the value 0b0000.

ProgMod, bits [3:0]

Support for the standard programmers' model for Armv4 and later. Model must support User, FIQ, IRQ, Supervisor, Abort, Undefined, and System modes. Defined values are:

ProgModMeaning
0b0000

Not supported.

0b0001

Supported.

All other values are reserved.

In Armv8-A the permitted values are 0b0001 and 0b0000.

If EL1 cannot use AArch32 then this field has the value 0b0000.

Accessing the ID_PFR1_EL1

Accesses to this register use the following encodings:

MRS <Xt>, ID_PFR1_EL1

op0op1CRnCRmop2
0b110b0000b00000b00010b001
if PSTATE.EL == EL0 then
    if IsFeatureImplemented("ARMv8.4-IDST") then
        if EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TGE == '1' then
            AArch64.SystemAccessTrap(EL2, 0x18);
        else
            AArch64.SystemAccessTrap(EL1, 0x18);
    else
        UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TID3 == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    else
        return ID_PFR1_EL1;
elsif PSTATE.EL == EL2 then
    return ID_PFR1_EL1;
elsif PSTATE.EL == EL3 then
    return ID_PFR1_EL1;
              


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