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ICC_BPR1, Interrupt Controller Binary Point Register 1

The ICC_BPR1 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 1 interrupt preemption.

Configuration

AArch32 System register ICC_BPR1 bits [31:0] (S) are architecturally mapped to AArch64 System register ICC_BPR1_EL1[31:0] (S) .

AArch32 System register ICC_BPR1 bits [31:0] (NS) are architecturally mapped to AArch64 System register ICC_BPR1_EL1[31:0] (NS) .

In GIC implementations supporting two Security states, this register is Banked.

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. If the PE resets into EL3 using AArch32 they apply only to the Secure instance of the register. Otherwise, RW fields in this register reset to architecturally UNKNOWN values.

Attributes

ICC_BPR1 is a 32-bit register.

Field descriptions

The ICC_BPR1 bit assignments are:

313029282726252423222120191817161514131211109876543210
00000000000000000000000000000BinaryPoint

Bits [31:3]

Reserved, RES0.

BinaryPoint, bits [2:0]

If the GIC is configured to use separate binary point fields for Group 0 and Group 1 interrupts, 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. For more information about priorities, see Priority grouping.

Writing 0 to this field will set this field to its reset value.

If EL3 is implemented and ICC_MCTLR.CBPR_EL1S is 1:

  • Accesses to this register at EL3 not in Monitor mode access the state of ICC_BPR0.
  • When SCR_EL3.EEL2 is 1 and HCR_EL2.IMO is 1, Secure accesses to this register at EL1 access the state of ICV_BPR1.
  • Otherwise, Secure accesses to this register at EL1 access the state of ICC_BPR0.

If EL3 is implemented and ICC_MCTLR.CBPR_EL1NS is 1, Non-secure accesses to this register at EL1 or EL2 behave as follows, depending on the values of HCR.IMO and SCR.IRQ:

HCR.IMOSCR_IRQBehavior
0b00b0Non-secure EL1 and EL2 reads return ICC_BPR0 + 1 saturated to 0b111. Non-secure EL1 and EL2 writes are ignored.
0b00b1Non-secure EL1 and EL2 accesses trap to EL3.
0b10b0Non-secure EL1 accesses affect virtual interrupts. Non-secure EL2 reads return ICC_BPR0 + 1 saturated to 0b111. Non-secure EL2 writes ignored.
0b10b1Non-secure EL1 accesses affect virtual interrupts. Non-secure EL2 accesses trap to EL3.

If EL3 is not implemented and ICC_CTLR.CBPR is 1, Non-secure accesses to this register at EL1 or EL2 behave as follows, depending on the values of HCR.IMO:

HCR.IMOBehavior
0b0Non-secure EL1 and EL2 reads return ICC_BPR0 + 1 saturated to 0b111. Non-secure EL1 and EL2 writes are ignored.
0b1Non-secure EL1 accesses affect virtual interrupts. Non-secure EL2 reads return ICC_BPR0 + 1 saturated to 0b111. Non-secure EL2 writes are ignored.

This field resets to an IMPLEMENTATION DEFINED non-zero value.

Accessing the ICC_BPR1

When the PE resets into an Exception level that is using AArch32, the reset value is equal to:

  • For the Secure copy of the register, the minimum value of ICC_BPR0 plus one.
  • For the Non-secure copy of the register, the minimum value of ICC_BPR0.

Where the minimum value of ICC_BPR0 is IMPLEMENTATION DEFINED.

If EL3 is not implemented:

  • If the PE is Secure this reset value is (minimum value of ICC_BPR0 plus one).
  • If the PE is Non-secure this reset value is (minimum value of ICC_BPR0).

An attempt to program the binary point field to a value less than the reset value sets the field to the reset value.

Accesses to this register use the following encodings:

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

opc1opc2CRncoprocCRm
0b0000b0110b11000b11110b1100
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.TALL1 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && ICH_HCR.TALL1 == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.IMO == '1' then
        return ICV_BPR1;
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR.IMO == '1' then
        return ICV_BPR1;
    elsif HaveEL(EL3) && !ELUsingAArch32(EL3) && SCR_EL3.IRQ == '1' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x03);
    elsif HaveEL(EL3) && ELUsingAArch32(EL3) && PSTATE.M != M32_Monitor && SCR.IRQ == '1' then
        AArch32.TakeMonitorTrapException();
    elsif HaveEL(EL3) then
        if SCR.NS == '0' then
            return ICC_BPR1_S;
        else
            return ICC_BPR1_NS;
    else
        return ICC_BPR1;
elsif PSTATE.EL == EL2 then
    if ICC_HSRE.SRE == '0' then
        UNDEFINED;
    elsif HaveEL(EL3) && !ELUsingAArch32(EL3) && SCR_EL3.IRQ == '1' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x03);
    elsif HaveEL(EL3) && ELUsingAArch32(EL3) && SCR.IRQ == '1' then
        AArch32.TakeMonitorTrapException();
    elsif HaveEL(EL3) then
        return ICC_BPR1_NS;
    else
        return ICC_BPR1;
elsif PSTATE.EL == EL3 then
    if ICC_MSRE.SRE == '0' then
        UNDEFINED;
    else
        if SCR.NS == '0' then
            return ICC_BPR1_S;
        else
            return ICC_BPR1_NS;
              

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

opc1opc2CRncoprocCRm
0b0000b0110b11000b11110b1100
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.TALL1 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && ICH_HCR.TALL1 == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.IMO == '1' then
        ICV_BPR1 = R[t];
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR.IMO == '1' then
        ICV_BPR1 = R[t];
    elsif HaveEL(EL3) && !ELUsingAArch32(EL3) && SCR_EL3.IRQ == '1' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x03);
    elsif HaveEL(EL3) && ELUsingAArch32(EL3) && PSTATE.M != M32_Monitor && SCR.IRQ == '1' then
        AArch32.TakeMonitorTrapException();
    elsif HaveEL(EL3) then
        if SCR.NS == '0' then
            ICC_BPR1_S = R[t];
        else
            ICC_BPR1_NS = R[t];
    else
        ICC_BPR1 = R[t];
elsif PSTATE.EL == EL2 then
    if ICC_HSRE.SRE == '0' then
        UNDEFINED;
    elsif HaveEL(EL3) && !ELUsingAArch32(EL3) && SCR_EL3.IRQ == '1' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x03);
    elsif HaveEL(EL3) && ELUsingAArch32(EL3) && SCR.IRQ == '1' then
        AArch32.TakeMonitorTrapException();
    elsif HaveEL(EL3) then
        ICC_BPR1_NS = R[t];
    else
        ICC_BPR1 = R[t];
elsif PSTATE.EL == EL3 then
    if ICC_MSRE.SRE == '0' then
        UNDEFINED;
    else
        if SCR.NS == '0' then
            ICC_BPR1_S = R[t];
        else
            ICC_BPR1_NS = R[t];
              


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