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GICV_IAR, Virtual Machine Interrupt Acknowledge Register

The GICV_IAR characteristics are:

Purpose

Provides the INTID of the signaled Group 0 virtual interrupt. A read of this register by the PE acts as an acknowledge for the interrupt.

This register corresponds to the physical CPU interface register GICC_IAR.

Configuration

This register is available when the GIC implementation supports interrupt virtualization.

Attributes

GICV_IAR is a 32-bit register.

Field descriptions

The GICV_IAR bit assignments are:

313029282726252423222120191817161514131211109876543210
RES0INTID

Bits [31:25]

Reserved, RES0.

INTID, bits [24:0]

The INTID of the signaled interrupt.

Note

INTIDs 1020-1023 are reserved and convey additional information such as spurious interrupts.

When affinity routing is not enabled:

  • Bits [23:13] are RES0.
  • For SGIs, bits [12:10] identify the CPU interface corresponding to the source PE. For all other interrupts these bits are RES0.

When the virtual machine writes to this register, the virtual CPU interface acknowledges the highest priority pending virtual interrupt and sets the state in the corresponding List register to active. The appropriate bit in the active priorities register GICH_APR<n> is set to 1.

If GICH_LR<n>.HW == 0, indicating that the interrupt is software-triggered, then bits [12:10] of GICH_LR<n> are returned in bits [12:10] of GICV_IAR. Otherwise bits [12:10] are RES0.

A read of this register returns the spurious INTID 1023 if either of the following is true:

  • There are no pending interrupts of sufficiently high priority value to be signaled to the PE with the virtual CPU interface enabled and GICH_HCR.En == 1.
  • Interrupt signaling by the virtual CPU interface is disabled.

A read of this register returns the spurious INTID 1022 if the highest priority pending interrupt is Group 1 and GICV_CTLR.AckCtl == 0.

Accessing the GICV_IAR

This register is used only when System register access is not enabled. When System register access is enabled:

  • For AArch32 implementations, ICC_IAR0 provides equivalent functionality.
  • For AArch64 implementations, ICC_IAR0_EL1 provides equivalent functionality.

This register is used for Group 0 interrupts only. GICV_AIAR provides equivalent functionality for Group 1 interrupts.

When affinity routing is enabled, it is a programming error to use memory-mapped registers to access the GIC.

GICV_IAR can be accessed through the memory-mapped interfaces:

ComponentOffsetInstance
GIC Virtual CPU interface0x000CGICV_IAR

This interface is accessible as follows:

  • When GICD_CTLR.DS == 0b0 access to this register is RO.
  • When IsAccessSecure() access to this register is RO.
  • When !IsAccessSecure() access to this register is RO.


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