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ICC_BPR0, Interrupt Controller Binary Point Register 0

The ICC_BPR0 characteristics are:

Purpose

Defines the point at which the priority value fields split into two parts, the group priority field and the subpriority field. The group priority field determines Group 0 interrupt preemption.

Configuration

AArch32 System register ICC_BPR0 bits [31:0] are architecturally mapped to AArch64 System register ICC_BPR0_EL1[31:0] .

RW fields in this register reset to architecturally UNKNOWN values.

Attributes

ICC_BPR0 is a 32-bit register.

Field descriptions

The ICC_BPR0 bit assignments are:

313029282726252423222120191817161514131211109876543210
00000000000000000000000000000BinaryPoint

Bits [31:3]

Reserved, RES0.

BinaryPoint, bits [2:0]

The value of this field controls how the 8-bit interrupt priority field is split into a group priority field, that determines interrupt preemption, and a subpriority field. This is done as follows:

Binary point valueGroup priority fieldSubpriority fieldField with binary point
0[7:1][0]ggggggg.s
1[7:2][1:0]gggggg.ss
2[7:3][2:0]ggggg.sss
3[7:4][3:0]gggg.ssss
4[7:5][4:0]ggg.sssss
5[7:6][5:0]gg.ssssss
6[7][6:0]g.sssssss
7No preemption[7:0].ssssssss

This field resets to an architecturally UNKNOWN value.

Accessing the ICC_BPR0

The minimum binary point value is derived from the number of implemented priority bits. The number of priority bits is IMPLEMENTATION DEFINED, and reported by ICC_CTLR.PRIbits and ICC_MCTLR.PRIbits.

An attempt to program the binary point field to a value less than the minimum value sets the field to the minimum value. On a reset, the binary point field is set to the minimum supported value.

Accesses to this register use the following encodings:

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

opc1opc2CRncoprocCRm
0b0000b0110b11000b11110b1000
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);
    elsif ICC_SRE.SRE == '0' then
        UNDEFINED;
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && ICH_HCR_EL2.TALL0 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && ICH_HCR.TALL0 == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.FMO == '1' then
        return ICV_BPR0;
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR.FMO == '1' then
        return ICV_BPR0;
    elsif HaveEL(EL3) && !ELUsingAArch32(EL3) && SCR_EL3.FIQ == '1' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x03);
    elsif HaveEL(EL3) && ELUsingAArch32(EL3) && PSTATE.M != M32_Monitor && SCR.FIQ == '1' then
        AArch32.TakeMonitorTrapException();
    else
        return ICC_BPR0;
elsif PSTATE.EL == EL2 then
    if ICC_HSRE.SRE == '0' then
        UNDEFINED;
    elsif HaveEL(EL3) && !ELUsingAArch32(EL3) && SCR_EL3.FIQ == '1' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x03);
    elsif HaveEL(EL3) && ELUsingAArch32(EL3) && SCR.FIQ == '1' then
        AArch32.TakeMonitorTrapException();
    else
        return ICC_BPR0;
elsif PSTATE.EL == EL3 then
    if ICC_MSRE.SRE == '0' then
        UNDEFINED;
    else
        return ICC_BPR0;
              

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

opc1opc2CRncoprocCRm
0b0000b0110b11000b11110b1000
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);
    elsif ICC_SRE.SRE == '0' then
        UNDEFINED;
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && ICH_HCR_EL2.TALL0 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && ICH_HCR.TALL0 == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.FMO == '1' then
        ICV_BPR0 = R[t];
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR.FMO == '1' then
        ICV_BPR0 = R[t];
    elsif HaveEL(EL3) && !ELUsingAArch32(EL3) && SCR_EL3.FIQ == '1' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x03);
    elsif HaveEL(EL3) && ELUsingAArch32(EL3) && PSTATE.M != M32_Monitor && SCR.FIQ == '1' then
        AArch32.TakeMonitorTrapException();
    else
        ICC_BPR0 = R[t];
elsif PSTATE.EL == EL2 then
    if ICC_HSRE.SRE == '0' then
        UNDEFINED;
    elsif HaveEL(EL3) && !ELUsingAArch32(EL3) && SCR_EL3.FIQ == '1' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x03);
    elsif HaveEL(EL3) && ELUsingAArch32(EL3) && SCR.FIQ == '1' then
        AArch32.TakeMonitorTrapException();
    else
        ICC_BPR0 = R[t];
elsif PSTATE.EL == EL3 then
    if ICC_MSRE.SRE == '0' then
        UNDEFINED;
    else
        ICC_BPR0 = R[t];
              


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