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GICD_IROUTER<n>, Interrupt Routing Registers, n = 32 - 1019

The GICD_IROUTER<n> characteristics are:

Purpose

When affinity routing is enabled, provides routing information for the SPI with INTID n.

Configuration

RW fields in this register reset to architecturally UNKNOWN values.

These registers are available in all configurations of the GIC. If the GIC implementation supports two Security states, these registers are Common.

The maximum value of n is given by (32*(GICD_TYPER.ITLinesNumber+1) - 1). GICD_IROUTER<n> registers where n=0 to 31 are reserved.

Attributes

GICD_IROUTER<n> is a 64-bit register.

Field descriptions

The GICD_IROUTER<n> bit assignments are:

6362616059585756555453525150494847464544434241403938373635343332
RES0Aff3
Interrupt_Routing_ModeRES0Aff2Aff1Aff0
313029282726252423222120191817161514131211109876543210

Bits [63:40]

Reserved, RES0.

Aff3, bits [39:32]

Affinity level 3, the least significant affinity level field.

This field resets to an architecturally UNKNOWN value.

Interrupt_Routing_Mode, bit [31]

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

Interrupt_Routing_ModeMeaning
0b0

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.

0b1

Interrupts routed to any PE defined as a participating node.

If GICD_IROUTER<n>.IRM == 0 and the affinity path does not correspond to an implemented PE, then if the corresponding interrupt becomes pending it will not be forwarded to any PE and will remain pending.

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>.{Aff3, Aff2, Aff1, Aff0} are UNKNOWN.

Note

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

This field resets to an architecturally UNKNOWN value.

Bits [30:24]

Reserved, RES0.

Aff2, bits [23:16]

Affinity level 2, an intermediate affinity level field.

This field resets to an architecturally UNKNOWN value.

Aff1, bits [15:8]

Affinity level 1, an intermediate affinity level field.

This field resets to an architecturally UNKNOWN value.

Aff0, bits [7:0]

Affinity level 0, the most significant affinity level field.

This field resets to an architecturally UNKNOWN value.

For an SPI with INTID m:

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

Accessing the GICD_IROUTER<n>

These registers are used only when affinity routing is enabled. When affinity routing is not enabled:

  • These registers are RES0. An implementation is permitted to make the register RAZ/WI in this case.
  • The GICD_ITARGETSR<n> registers provide interrupt routing information.
Note

When affinity routing becomes enabled for a Security state (for example, following a reset or following a write to GICD_CTLR) the value of all writeable fields in this register is UNKNOWN for that Security state. When the group of an interrupt changes so the ARE setting for the interrupt changes to 1, the value of this register is UNKNOWN for that interrupt.

If GICD_CTLR.DS==0, unless the GICD_NSACR<n> registers permit Non-secure software to control Group 0 and Secure Group 1 interrupts, any GICD_IROUTER<n> registers that correspond to Group 0 or Secure Group 1 interrupts are accessible only by Secure accesses and are RAZ/WI to Non-secure accesses.

Note

For each interrupt, a GIC implementation might support fewer than 256 values for an affinity level. In this case, some bits of the corresponding affinity level field might be RO. Implementations must ensure that an interrupt that is pending at the time of the write uses either the old value or the new value and must ensure that the interrupt is neither lost nor handled more than one time. The effect of the change must be visible in finite time.

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

ComponentOffsetInstance
GIC Distributor0x6000 + 8nGICD_IROUTER<n>

This interface is accessible as follows:

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


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