Interrupt Controller Virtual Interrupt Acknowledge Register 0
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.
AArch32 System register ICV_IAR0 bits [31:0] performs the same function as AArch64 System register ICV_IAR0_EL1[31:0].
This register is present only when FEAT_AA32EL1 is implemented, GICv3 is implemented, and EL2 is implemented. Otherwise, direct accesses to ICV_IAR0 are UNDEFINED.
When virtual FIQs are masked by the PE, the side-effects of direct reads of ICV_IAR0 that updates the Running priority and affect signaling of an interrupt exception are guaranteed to be visible to later instructions in the Execution stream. For information on PE interrupt masking see Arm® Architecture Reference Manual for A-profile architecture. 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).
ICV_IAR0 is a 32-bit register.
| 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 | ||||||||||||||||||||||||||||||
Reserved, RES0.
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.
Accesses to this register use the following encodings in the System register encoding space:
MRC{<c>}{<q>} <coproc>, {#}<opc1>, <Rt>, <CRn>, <CRm>{, {#}<opc2>}
(coproc = 0b1111, opc1 = 0b000, CRn = 0b1100, CRm = 0b1000, opc2 = 0b000)
if !(IsFeatureImplemented(FEAT_AA32EL1) && IsFeatureImplemented(FEAT_GICv3)) then Undefined(); elsif HaveEL(EL3) && PSTATE.EL IN {EL1, EL2} && EL3SDDUndefPriority() && IsFeatureImplemented(FEAT_AA64EL3) && !ELUsingAArch32(EL3) && SCR_EL3().FIQ == '1' then Undefined(); elsif HaveEL(EL3) && PSTATE.EL IN {EL1, EL2} && EL3SDDUndefPriority() && IsFeatureImplemented(FEAT_AA32EL3) && ELUsingAArch32(EL3) && SCR().FIQ == '1' then Undefined(); elsif PSTATE.EL == EL0 then Undefined(); elsif PSTATE.EL == EL1 then if EL2Enabled() && IsFeatureImplemented(FEAT_AA64EL2) && !ELUsingAArch32(EL2) && HSTR_EL2().T12 == '1' then AArch64_AArch32SystemAccessTrap(EL2, 0x03); elsif EL2Enabled() && IsFeatureImplemented(FEAT_AA32EL2) && ELUsingAArch32(EL2) && HSTR().T12 == '1' then AArch32_TakeHypTrapException(0x03); elsif ICC_SRE().SRE == '0' then Undefined(); elsif EL2Enabled() && IsFeatureImplemented(FEAT_AA64EL2) && !ELUsingAArch32(EL2) && ICH_HCR_EL2().TALL0 == '1' then AArch64_AArch32SystemAccessTrap(EL2, 0x03); elsif EL2Enabled() && IsFeatureImplemented(FEAT_AA32EL2) && ELUsingAArch32(EL2) && ICH_HCR().TALL0 == '1' then AArch32_TakeHypTrapException(0x03); elsif EL2Enabled() && IsFeatureImplemented(FEAT_AA64EL2) && !ELUsingAArch32(EL2) && HCR_EL2().FMO == '1' then R(t) = ICV_IAR0(); elsif EL2Enabled() && IsFeatureImplemented(FEAT_AA32EL2) && ELUsingAArch32(EL2) && HCR().FMO == '1' then R(t) = ICV_IAR0(); elsif HaveEL(EL3) && IsFeatureImplemented(FEAT_AA64EL3) && !ELUsingAArch32(EL3) && SCR_EL3().FIQ == '1' then if EL3SDDUndef() then Undefined(); else AArch64_AArch32SystemAccessTrap(EL3, 0x03); end; elsif HaveEL(EL3) && IsFeatureImplemented(FEAT_AA32EL3) && ELUsingAArch32(EL3) && SCR().FIQ == '1' then Undefined(); else R(t) = ICC_IAR0(); end; elsif PSTATE.EL == EL2 then if ICC_HSRE().SRE == '0' then Undefined(); elsif HaveEL(EL3) && IsFeatureImplemented(FEAT_AA64EL3) && !ELUsingAArch32(EL3) && SCR_EL3().FIQ == '1' then if EL3SDDUndef() then Undefined(); else AArch64_AArch32SystemAccessTrap(EL3, 0x03); end; elsif HaveEL(EL3) && IsFeatureImplemented(FEAT_AA32EL3) && ELUsingAArch32(EL3) && SCR().FIQ == '1' then Undefined(); else R(t) = ICC_IAR0(); end; elsif PSTATE.EL == EL3 then if ICC_MSRE().SRE == '0' then Undefined(); elsif SCR().FIQ == '1' && PSTATE.M != M32_Monitor then Undefined(); else R(t) = ICC_IAR0(); end; end;
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