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GICD_IROUTER<n>E, Interrupt Routing Registers (Extended SPI Range), n = 0 - 1023

The GICD_IROUTER<n>E characteristics are:


When affinity routing is enabled, provides routing information for the corresponding SPI in the extended SPI range.


This register is present only when FEAT_GICv3p1 is implemented. Otherwise, direct accesses to GICD_IROUTER<n>E are RES0.

RW fields in this register reset to architecturally UNKNOWN values.

When GICD_TYPER.ESPI==0, these registers are RES0.

When GICD_TYPER.ESPI==1, the number of implemented GICD_IROUTER<n>E registers is (((GICD_TYPER.ESPI_range+1)*32)-1). Registers are numbered from 0.


GICD_IROUTER<n>E is a 64-bit register.

Field descriptions

The GICD_IROUTER<n>E bit assignments are:


Bits [63:40]

Reserved, RES0.

Aff3, bits [39:32]

Affinity level 3, the least significant affinity level field.

Interrupt_Routing_Mode, bit [31]

Interrupt Routing Mode. Defines how SPIs are routed in an affinity hierarchy:


Interrupts routed to the PE specified by a.b.c.d. In this routing, a, b, c, and d are the values of fields Aff3, Aff2, Aff1, and Aff0 respectively.


Interrupts routed to any PE defined as a participating node.

If GICD_IROUTER<n>E.IRM == 0 and the affinity path does not correspond to an implemented PE, then if the corresponding interrupt becomes pending behavior is CONSTRAINED UNPREDICTABLE:

  • The interrupt is not forwarded to any PE, direct reads return the written value

  • The affinity path is treated as an UNKNOWN implemented PE, direct reads return the UNKNOWN implemented PE

  • The affinity path is treated as an UNKNOWN implemented PE, direct reads return the written value

In implementations that do not require 1 of N distribution of SPIs, this bit might be RAZ/WI.

When this bit is set to 1, GICD_IROUTER<n>E.{Aff3, Aff2, Aff1, Aff0} are UNKNOWN.


An implementation might choose to make the Aff<n> fields RO when this field is 1.

Bits [30:24]

Reserved, RES0.

Aff2, bits [23:16]

Affinity level 2, an intermediate affinity level field.

Aff1, bits [15:8]

Affinity level 1, an intermediate affinity level field.

Aff0, bits [7:0]

Affinity level 0, the most significant affinity level field.

For an SPI with INTID m:

  • The corresponding GICD_IROUTER<n>E register number, n, is given by n = m.
  • The offset of the GICD_IROUTER<n>E register is 0x6000 + 8n.

Accessing the GICD_IROUTER<n>E

When affinity routing is not enabled for the Security state of an interrupt in GICD_IROUTER<n>E, the register is RES0.

When GICD_CTLR.DS==0, a register that corresponds to a Group 0 or Secure Group 1 interrupt is RAZ/WI to Non-secure accesses.

Bits corresponding to unimplemented interrupts are RAZ/WI.

GICD_IROUTER<n>E can be accessed through the memory-mapped interfaces:

GIC Distributor0x8000 + (8 * n)GICD_IROUTER<n>E

This interface is accessible as follows:

  • When GICD_CTLR.DS == 0 accesses to this register are RW.
  • When an access is Secure accesses to this register are RW.
  • When an access is Non-secure accesses to this register are RW.