ICC_IAR1, Interrupt Controller Interrupt Acknowledge Register 1

The ICC_IAR1 characteristics are:

Purpose

The PE reads this register to obtain the INTID of the signaled Group 1 interrupt. This read acts as an acknowledge for the interrupt.

Configuration

AArch32 System register ICC_IAR1 performs the same function as AArch64 System register ICC_IAR1_EL1.

To allow software to ensure appropriate observability of actions initiated by GIC register accesses, the PE and CPU interface logic must ensure that reads of this register are self-synchronising when interrupts are masked by the PE (that is when PSTATE.{I,F} == {0,0}). This ensures that the effect of activating an interrupt on the signaling of interrupt exceptions is observed when a read of this register is architecturally executed so that no spurious interrupt exception occurs if interrupts are unmasked by an instruction immediately following the read. See Observability of the effects of accesses to the GIC registers, for more information.

Attributes

ICC_IAR1 is a 32-bit register.

Field descriptions

The ICC_IAR1 bit assignments are:

Bits [31:24]

Reserved, RES0.

INTID, bits [23:0]

The INTID of the signaled interrupt.

This is the INTID of the highest priority pending interrupt, if that interrupt is of sufficient priority for it to be signaled to the PE, and if it can be acknowledged at the current Security state and Exception level.

If the highest priority pending interrupt is not observable, this field contains a special INTID to indicate the reason. This special INTID can take the value 1023 only. See Special INTIDs, for more information.

This field has either 16 or 24 bits implemented. The number of implemented bits can be found in ICC_CTLR.IDbits and ICC_MCTLR.IDbits. If only 16 bits are implemented, bits [23:16] of this register are RES0.

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_IAR1;
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR.IMO == '1' then
        return ICV_IAR1;
    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();
    else
        return ICC_IAR1;
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();
    else
        return ICC_IAR1;
elsif PSTATE.EL == EL3 then
    if ICC_MSRE.SRE == '0' then
        UNDEFINED;
    else
        return ICC_IAR1;