GICC_EOIR, CPU Interface End Of Interrupt Register
The GICC_EOIR characteristics are:
- This register is Common.
- GICC_AEOIR is an alias of the Non-secure view of this register.
For Non-secure writes when GICD_CTLR.DS==1, the register provides functionality for Group 1 interrupts.
GICC_EOIR is a 32-bit register.
The GICC_EOIR bit assignments are:
INTID, bits [23:0]
The INTID of the signaled interrupt.
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.
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.
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, see 'Interrupt lifecycle' in ARM® Generic Interrupt Controller Architecture Specification, GIC architecture version 3.0 and version 4.0 (ARM IHI 0069).
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:
- For AArch32 implementations, ICC_EOIR0 and ICC_EOIR1 provide equivalent functionality.
- For AArch64 implementations, ICC_EOIR0_EL1 and ICC_EOIR1_EL1 provide equivalent functionality.
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:
|GIC CPU interface||0x0010||GICC_EOIR|
This interface is accessible as follows:
- When GICD_CTLR.DS == 0b0 accesses to this register are WO.
- When IsAccessSecure() accesses to this register are WO.
- When !IsAccessSecure() accesses to this register are WO.