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GICD_ISENABLER<n>, Interrupt Set-Enable Registers, n = 0 - 31

The GICD_ISENABLER<n> characteristics are:

Purpose

Enables forwarding of the corresponding interrupt to the CPU interfaces.

Configuration

These registers are available in all GIC configurations. If GICD_CTLR.DS==0, these registers are Common.

The number of implemented GICD_ISENABLER<n> registers is (GICD_TYPER.ITLinesNumber+1). Registers are numbered from 0.

GICD_ISENABLER0 is Banked for each connected PE with GICR_TYPER.Processor_Number < 8.

Accessing GICD_ISENABLER0 from a PE with GICR_TYPER.Processor_Number > 7 is CONSTRAINED UNPREDICTABLE:

  • Register is RAZ/WI.
  • An UNKNOWN banked copy of the register is accessed.

Attributes

GICD_ISENABLER<n> is a 32-bit register.

Field descriptions

The GICD_ISENABLER<n> bit assignments are:

313029282726252423222120191817161514131211109876543210
Set_enable_bit31Set_enable_bit30Set_enable_bit29Set_enable_bit28Set_enable_bit27Set_enable_bit26Set_enable_bit25Set_enable_bit24Set_enable_bit23Set_enable_bit22Set_enable_bit21Set_enable_bit20Set_enable_bit19Set_enable_bit18Set_enable_bit17Set_enable_bit16Set_enable_bit15Set_enable_bit14Set_enable_bit13Set_enable_bit12Set_enable_bit11Set_enable_bit10Set_enable_bit9Set_enable_bit8Set_enable_bit7Set_enable_bit6Set_enable_bit5Set_enable_bit4Set_enable_bit3Set_enable_bit2Set_enable_bit1Set_enable_bit0

Set_enable_bit<x>, bit [x], for x = 31 to 0

For SPIs and PPIs, controls the forwarding of interrupt number 32n + x to the CPU interfaces. Reads and writes have the following behavior:

Set_enable_bit<x>Meaning
0b0

If read, indicates that forwarding of the corresponding interrupt is disabled.

If written, has no effect.

0b1

If read, indicates that forwarding of the corresponding interrupt is enabled.

If written, enables forwarding of the corresponding interrupt.

After a write of 1 to this bit, a subsequent read of this bit returns 1.

For SGIs, the behavior of this bit is IMPLEMENTATION DEFINED.

On a Warm reset, this field resets to an architecturally UNKNOWN value.

For INTID m, when DIV and MOD are the integer division and modulo operations:

  • The corresponding GICD_ISENABLER<n> number, n, is given by n = m DIV 32.
  • The offset of the required GICD_ISENABLER is (0x100 + (4*n)).
  • The bit number of the required group modifier bit in this register is m MOD 32.

At start-up, and after a reset, a PE can use this register to discover which peripheral INTIDs the GIC supports. If GICD_CTLR.DS==0 in a system that supports EL3, the PE must do this for the Secure view of the available interrupts, and Non-secure software running on the PE must do this discovery after the Secure software has configured interrupts as Group 0/Secure Group 1 and Non-secure Group 1.

Accessing the GICD_ISENABLER<n>

For SGIs and PPIs:

  • When ARE is 1 for the Security state of an interrupt, the field for that interrupt is RES0 and an implementation is permitted to make the field RAZ/WI in this case.
  • Equivalent functionality is provided by GICR_ISENABLER0.

Bits corresponding to unimplemented interrupts are RAZ/WI.

When GICD_CTLR.DS==0, bits corresponding to Group 0 or Secure Group 1 interrupts are RAZ/WI to Non-secure accesses.

It is IMPLEMENTATION DEFINED whether implemented SGIs are permanently enabled, or can be enabled and disabled by writes to GICD_ISENABLER<n> and GICD_ICENABLER<n> where n=0.

For SPIs and PPIs, each bit controls the forwarding of the corresponding interrupt from the Distributor to the CPU interfaces.

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

ComponentOffsetInstance
GIC Distributor0x0100 + (4 * n)GICD_ISENABLER<n>

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.


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