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# ICV_IAR0, Interrupt Controller Virtual Interrupt Acknowledge Register 0

The ICV_IAR0 characteristics are:

## Purpose

The PE reads this register to obtain the INTID of the signaled virtual Group 0 interrupt. This read acts as an acknowledge for the interrupt.

## Configuration

AArch32 System register ICV_IAR0 performs the same function as AArch64 System register ICV_IAR0_EL1.

This register is present only when EL1 is capable of using AArch32, GICv3 is implemented and EL2 is implemented. Otherwise, direct accesses to ICV_IAR0 are UNDEFINED.

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. For more information, see 'Observability of the effects of accesses to the GIC registers' in ARM® Generic Interrupt Controller Architecture Specification, GIC architecture version 3.0 and version 4.0 (ARM IHI 0069).

## Attributes

ICV_IAR0 is a 32-bit register.

## Field descriptions

31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0
RES0 | INTID

#### Bits [31:24]

Reserved, RES0.

#### INTID, bits [23:0]

The INTID of the signaled virtual interrupt.

This is the INTID of the highest priority pending virtual interrupt, if that interrupt is of sufficient priority for it to be signaled to the PE, and if it can be acknowledged.

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. For more information, see 'Special INTIDs' in ARM® Generic Interrupt Controller Architecture Specification, GIC architecture version 3.0 and version 4.0 (ARM IHI 0069).

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

## Accessing ICV_IAR0

Accesses to this register use the following encodings in the System register encoding space:

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

coproc | opc1 | CRn | CRm | opc2
--- | --- | --- | --- | ---
0b1111 | 0b000 | 0b1100 | 0b1000 | 0b000

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if HaveEL(EL3) && EL3SDDUndefPriority() && !ELUsingAArch32(EL3) && SCR_EL3.FIQ == '1' then UNDEFINED; elsif HaveEL(EL3) && EL3SDDUndefPriority() && ELUsingAArch32(EL3) && PSTATE.M != M32_Monitor && SCR.FIQ == '1' then UNDEFINED; elsif 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 R[t] = ICV_IAR0; elsif EL2Enabled() && ELUsingAArch32(EL2) && HCR.FMO == '1' then R[t] = ICV_IAR0; elsif HaveEL(EL3) && !ELUsingAArch32(EL3) && SCR_EL3.FIQ == '1' then if EL3SDDUndef() then UNDEFINED; else AArch64.AArch32SystemAccessTrap(EL3, 0x03); elsif HaveEL(EL3) && ELUsingAArch32(EL3) && PSTATE.M != M32_Monitor && SCR.FIQ == '1' then if EL3SDDUndef() then UNDEFINED; else AArch32.TakeMonitorTrapException(); else R[t] = ICC_IAR0; elsif PSTATE.EL == EL2 then if HaveEL(EL3) && EL3SDDUndefPriority() && !ELUsingAArch32(EL3) && SCR_EL3.FIQ == '1' then UNDEFINED; elsif HaveEL(EL3) && EL3SDDUndefPriority() && ELUsingAArch32(EL3) && SCR.FIQ == '1' then UNDEFINED; elsif ICC_HSRE.SRE == '0' then UNDEFINED; elsif HaveEL(EL3) && !ELUsingAArch32(EL3) && SCR_EL3.FIQ == '1' then if EL3SDDUndef() then UNDEFINED; else AArch64.AArch32SystemAccessTrap(EL3, 0x03); elsif HaveEL(EL3) && ELUsingAArch32(EL3) && SCR.FIQ == '1' then if EL3SDDUndef() then UNDEFINED; else AArch32.TakeMonitorTrapException(); else R[t] = ICC_IAR0; elsif PSTATE.EL == EL3 then if ICC_MSRE.SRE == '0' then UNDEFINED; else R[t] = ICC_IAR0;

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26/03/2024 09:49; 67c0ae5282a7629ba0ea0ba7267b43cd4f7939f6

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