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ICC_MSRE, Interrupt Controller Monitor System Register Enable register

The ICC_MSRE characteristics are:

Purpose

Controls whether the System register interface or the memory-mapped interface to the GIC CPU interface is used for EL3.

Configuration

AArch32 System register ICC_MSRE bits [31:0] can be mapped to AArch64 System register ICC_SRE_EL3[31:0] , but this is not architecturally mandated.

Some or all RW fields of this register have defined reset values. These apply only if the PE resets into an Exception level that is using AArch32. Otherwise, RW fields in this register reset to architecturally UNKNOWN values.

Attributes

ICC_MSRE is a 32-bit register.

Field descriptions

The ICC_MSRE bit assignments are:

313029282726252423222120191817161514131211109876543210
RES0EnableDIBDFBSRE

Bits [31:4]

Reserved, RES0.

Enable, bit [3]

Enable. Enables lower Exception level access to ICC_SRE and ICC_HSRE.

EnableMeaning
0b0

Secure EL1 accesses to Secure ICC_SRE trap to EL3.

EL2 accesses to Non-secure ICC_SRE and ICC_HSRE trap to EL3.

Non-secure EL1 accesses to ICC_SRE trap to EL3, unless these accesses are trapped to EL2 as a result of ICC_HSRE.Enable == 0.

0b1

Secure EL1 accesses to Secure ICC_SRE do not trap to EL3.

EL2 accesses to Non-secure ICC_SRE and ICC_HSRE do not trap to EL3.

Non-secure EL1 accesses to ICC_SRE do not trap to EL3.

If ICC_MSRE.SRE is RAO/WI, an implementation is permitted to make the Enable bit RAO/WI.

If ICC_MSRE.SRE is 0, the Enable bit behaves as 1 for all purposes other than reading the value of the bit.

This field resets to an architecturally UNKNOWN value.

DIB, bit [2]

Disable IRQ bypass.

DIBMeaning
0b0

IRQ bypass enabled.

0b1

IRQ bypass disabled.

In systems that do not support IRQ bypass, this bit is RAO/WI.

This field resets to 0.

DFB, bit [1]

Disable FIQ bypass.

DFBMeaning
0b0

FIQ bypass enabled.

0b1

FIQ bypass disabled.

In systems that do not support FIQ bypass, this bit is RAO/WI.

This field resets to 0.

SRE, bit [0]

System Register Enable.

SREMeaning
0b0

The memory-mapped interface must be used. Accesses at EL3 or below to any ICH_* System register, or any EL1, EL2, or EL3 ICC_* register other than ICC_SRE, ICC_HSRE, or ICC_MSRE, are UNDEFINED.

0b1

The System register interface to the ICH_* registers and the EL1, EL2, and EL3 ICC_* registers is enabled for EL3.

If software changes this bit from 1 to 0, the results are UNPREDICTABLE.

If an implementation supports only a System register interface to the GIC CPU interface, this bit is RAO/WI.

This field resets to 0.

Accessing the ICC_MSRE

This register is always System register accessible.

The GIC architecture permits, but does not require, that registers can be shared between memory-mapped registers and the equivalent System registers. This means that if the memory-mapped registers have been accessed while ICC_MSRE.SRE==0, then the System registers might be modified. Therefore, software must only rely on the reset values of the System registers if there has been no use of the GIC functionality while the memory-mapped registers are in use. Otherwise, the System register values must be treated as UNKNOWN.

This register is only accessible when executing in Monitor mode.

Accesses to this register use the following encodings:

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

coprocopc1CRnCRmopc2
0b11110b1100b11000b11000b101
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T12 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T12 == '1' then
        AArch32.TakeHypTrapException(0x03);
    else
        UNDEFINED;
elsif PSTATE.EL == EL2 then
    UNDEFINED;
elsif PSTATE.EL == EL3 then
    return ICC_MSRE;

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

coprocopc1CRnCRmopc2
0b11110b1100b11000b11000b101
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T12 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T12 == '1' then
        AArch32.TakeHypTrapException(0x03);
    else
        UNDEFINED;
elsif PSTATE.EL == EL2 then
    UNDEFINED;
elsif PSTATE.EL == EL3 then
    if SCR.NS == '0' && CP15SDISABLE2 == HIGH then
        UNDEFINED;
    else
        ICC_MSRE = R[t];


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