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FPSID, Floating-Point System ID register

The FPSID characteristics are:

Purpose

Provides top-level information about the floating-point implementation.

This register largely duplicates information held in the MIDR. Arm deprecates use of it.

Configuration

Implemented only if the implementation includes the Advanced SIMD and floating-point functionality.

RW fields in this register reset to architecturally UNKNOWN values.

Attributes

FPSID is a 32-bit register.

Field descriptions

The FPSID bit assignments are:

313029282726252423222120191817161514131211109876543210
ImplementerSWSubarchitecturePartNumVariantRevision

Implementer, bits [31:24]

Implementer codes are the same as those used for the MIDR.

For an implementation by Arm this field is 0x41, the ASCII code for A.

This field resets to an architecturally UNKNOWN value.

SW, bit [23]

Software bit. Defined values are:

SWMeaning
0b0

The implementation provides a hardware implementation of the floating-point instructions.

0b1

The implementation supports only software emulation of the floating-point instructions.

In Armv8-A the only permitted value is 0b0.

This field resets to an architecturally UNKNOWN value.

Subarchitecture, bits [22:16]

Subarchitecture version number. For an implementation by Arm, defined values are:

SubarchitectureMeaning
0b0000000

VFPv1 architecture with an IMPLEMENTATION DEFINED subarchitecture.

0b0000001

VFPv2 architecture with Common VFP subarchitecture v1.

0b0000010

VFPv3 architecture, or later, with Common VFP subarchitecture v2. The VFP architecture version is indicated by the MVFR0 and MVFR1 registers.

0b0000011

VFPv3 architecture, or later, with Null subarchitecture. The entire floating-point implementation is in hardware, and no software support code is required. The VFP architecture version is indicated by the MVFR0 and MVFR1 registers. This value can be used only by an implementation that does not support the trap enable bits in the FPSCR.

0b0000100

VFPv3 architecture, or later, with Common VFP subarchitecture v3, and support for trap enable bits in FPSCR. The VFP architecture version is indicated by the MVFR0 and MVFR1 registers.

For a subarchitecture designed by Arm the most significant bit of this field, register bit[22], is 0. Values with a most significant bit of 0 that are not listed here are reserved.

When the subarchitecture designer is not Arm, the most significant bit of this field, register bit[22], must be 1. Each implementer must maintain its own list of subarchitectures it has designed, starting at subarchitecture version number 0x40.

In Armv8-A the permitted values are 0b0000011 and 0b0000100.

This field resets to an architecturally UNKNOWN value.

PartNum, bits [15:8]

An IMPLEMENTATION DEFINED part number for the floating-point implementation, assigned by the implementer.

This field resets to an architecturally UNKNOWN value.

Variant, bits [7:4]

An IMPLEMENTATION DEFINED variant number. Typically, this field distinguishes between different production variants of a single product.

This field resets to an architecturally UNKNOWN value.

Revision, bits [3:0]

An IMPLEMENTATION DEFINED revision number for the floating-point implementation.

This field resets to an architecturally UNKNOWN value.

Accessing the FPSID

Accesses to this register use the following encodings:

VMRS{<c>}{<q>} <Rt>, <spec_reg>

reg
0b0000
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if ELUsingAArch32(EL1) && ((ELUsingAArch32(EL3) && SCR.NS == '1' && NSACR.cp10 == '0') || CPACR.cp10 == '00') then
        UNDEFINED;
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.E2H != '1' && CPTR_EL2.TFP == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x07);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.E2H == '1' && CPTR_EL2.FPEN == 'x0' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x07);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && ((ELUsingAArch32(EL3) && SCR.NS == '1' && NSACR.cp10 == '0') || HCPTR.TCP10 == '1') then
        AArch32.TakeHypTrapException(0x08);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TID3 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x08);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HCR.TID3 == '1' then
        AArch32.TakeHypTrapException(0x08);
    else
        return FPSID;
elsif PSTATE.EL == EL2 then
    if HCR_EL2.E2H == '0' && CPTR_EL2.TFP == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x07);
    elsif HCR_EL2.E2H == '1' && CPTR_EL2.FPEN == 'x0' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x07);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && ((ELUsingAArch32(EL3) && SCR.NS == '1' && NSACR.cp10 == '0') || HCPTR.TCP10 == '1') then
        AArch32.TakeHypTrapException(0x00);
    else
        return FPSID;
elsif PSTATE.EL == EL3 then
    if CPACR.cp10 == '00' then
        UNDEFINED;
    else
        return FPSID;

VMSR{<c>}{<q>} <spec_reg>, <Rt>

reg
0b0000
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if ELUsingAArch32(EL1) && ((ELUsingAArch32(EL3) && SCR.NS == '1' && NSACR.cp10 == '0') || CPACR.cp10 == '00') then
        UNDEFINED;
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.E2H != '1' && CPTR_EL2.TFP == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x07);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.E2H == '1' && CPTR_EL2.FPEN == 'x0' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x07);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && ((ELUsingAArch32(EL3) && SCR.NS == '1' && NSACR.cp10 == '0') || HCPTR.TCP10 == '1') then
        AArch32.TakeHypTrapException(0x08);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TID3 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x08);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HCR.TID3 == '1' then
        AArch32.TakeHypTrapException(0x08);
    else
        //no operation
elsif PSTATE.EL == EL2 then
    if HCR_EL2.E2H == '0' && CPTR_EL2.TFP == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x07);
    elsif HCR_EL2.E2H == '1' && CPTR_EL2.FPEN == 'x0' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x07);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && ((ELUsingAArch32(EL3) && SCR.NS == '1' && NSACR.cp10 == '0') || HCPTR.TCP10 == '1') then
        AArch32.TakeHypTrapException(0x00);
    else
        //no operation
elsif PSTATE.EL == EL3 then
    if CPACR.cp10 == '00' then
        UNDEFINED;
    else
        //no operation


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