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GICC_EOIR, CPU Interface End Of Interrupt Register

The GICC_EOIR characteristics are:

Purpose

A write to this register performs priority drop for the specified interrupt and, if the appropriate GICC_CTLR.EOImodeS or GICC_CTLR.EOImodeNS field == 0, also deactivates the interrupt.

Configuration

If GICD_CTLR.DS==0:

  • This register is Common.
  • GICC_AEOIR is an alias of the Non-secure view of this register.

For Secure writes when GICD_CTLR.DS==0, or for Secure and Non-secure writes when GICD_CTLR.DS==1, the register provides functionality for Group 0 interrupts.

For Non-secure writes when GICD_CTLR.DS==1, the register provides functionality for Group 1 interrupts.

Attributes

GICC_EOIR is a 32-bit register.

Field descriptions

The GICC_EOIR bit assignments are:

313029282726252423222120191817161514131211109876543210
RES0INTID

Bits [31:24]

Reserved, RES0.

INTID, bits [23:0]

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.

For every read of a valid INTID from GICC_IAR, the connected PE must perform a matching write to GICC_EOIR. The value written to GICC_EOIR must be the INTID from GICC_IAR. Reads of INTIDs 1020-1023 do not require matching writes.

Note

Arm recommends that software preserves the entire register value read from GICC_IAR, and writes that value back to GICC_EOIR on completion of interrupt processing.

For nested interrupts, the order of writes to this register must be the reverse of the order of interrupt acknowledgement. Behavior is UNPREDICTABLE if:

  • This ordering constraint is not maintained.
  • The value written to this register does not match an active interrupt, or the ID of a spurious interrupt.
  • The value written to this register does not match the last valid interrupt value read from GICC_IAR.

See Interrupt lifecycle for general information about the effect of writes to end of interrupt registers, and about the possible separation of the priority drop and interrupt deactivate operations.

If GICD_CTLR.DS==0:

Accessing the GICC_EOIR

The following writes must be ignored:

  • Writes of INTIDs 1020-1023.
  • Secure writes corresponding to Group 1 interrupts. In systems that support system error generation, an implementation might generate a system error. In this case, GIC behavior is predictable, and the highest Secure active priority (in the Secure copy of GICC_APR<n>) will be reset if the highest active priority is Secure. System behavior is UNPREDICTABLE.
  • Non-secure writes corresponding to Group 0 interrupts when GICC_CTLR.EOImodeS == 1. In systems that support system error generation, an implementation might generate a system error. In this case, GIC behavior is predictable, and the highest Non-secure active priority (in the Non-secure copy of GICC_APR<n>) will be reset if the highest active priority is Non-secure. System behavior is UNPREDICTABLE.

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

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

GICC_EOIR can be accessed through the memory-mapped interfaces:

ComponentOffsetInstance
GIC CPU interface0x0010GICC_EOIR

This interface is accessible as follows:

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


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