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CONTEXTIDR, Context ID Register

The CONTEXTIDR characteristics are:

Purpose

Identifies the current Process Identifier and, when using the Short-descriptor translation table format, the Address Space Identifier.

The value of the whole of this register is called the Context ID and is used by:

  • The debug logic, for Linked and Unlinked Context ID matching.
  • The trace logic, to identify the current process.

The significance of this register is for debug and trace use only.

Configuration

AArch32 System register CONTEXTIDR bits [31:0] are architecturally mapped to AArch64 System register CONTEXTIDR_EL1[31:0] .

The register format depends on whether address translation is using the Long-descriptor or the Short-descriptor translation table format.

RW fields in this register reset to architecturally UNKNOWN values.

Attributes

CONTEXTIDR is a 32-bit register.

Field descriptions

The CONTEXTIDR bit assignments are:

When TTBCR.EAE == 0:
313029282726252423222120191817161514131211109876543210
PROCIDASID

PROCID, bits [31:8]

Process Identifier. This field must be programmed with a unique value that identifies the current process.

This field resets to an architecturally UNKNOWN value.

ASID, bits [7:0]

Address Space Identifier. This field is programmed with the value of the current ASID.

This field resets to an architecturally UNKNOWN value.

When TTBCR.EAE == 1:
313029282726252423222120191817161514131211109876543210
PROCID

PROCID, bits [31:0]

Process Identifier. This field must be programmed with a unique value that identifies the current process.

This field resets to an architecturally UNKNOWN value.

Accessing the CONTEXTIDR

Accesses to this register use the following encodings:

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

coprocopc1CRnCRmopc2
0b11110b0000b11010b00000b001
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T13 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T13 == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TRVM == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HCR.TRVM == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif HaveEL(EL3) && ELUsingAArch32(EL3) then
        if SCR.NS == '0' then
            return CONTEXTIDR_S;
        else
            return CONTEXTIDR_NS;
    else
        return CONTEXTIDR;
elsif PSTATE.EL == EL2 then
    if HaveEL(EL3) && ELUsingAArch32(EL3) then
        return CONTEXTIDR_NS;
    else
        return CONTEXTIDR;
elsif PSTATE.EL == EL3 then
    if SCR.NS == '0' then
        return CONTEXTIDR_S;
    else
        return CONTEXTIDR_NS;
              

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

coprocopc1CRnCRmopc2
0b11110b0000b11010b00000b001
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T13 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T13 == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TVM == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HCR.TVM == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif HaveEL(EL3) && ELUsingAArch32(EL3) then
        if SCR.NS == '0' then
            CONTEXTIDR_S = R[t];
        else
            CONTEXTIDR_NS = R[t];
    else
        CONTEXTIDR = R[t];
elsif PSTATE.EL == EL2 then
    if HaveEL(EL3) && ELUsingAArch32(EL3) then
        CONTEXTIDR_NS = R[t];
    else
        CONTEXTIDR = R[t];
elsif PSTATE.EL == EL3 then
    if SCR.NS == '0' then
        CONTEXTIDR_S = R[t];
    else
        CONTEXTIDR_NS = R[t];
              


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