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GICD_IPRIORITYR<n>, Interrupt Priority Registers, n = 0 - 254

The GICD_IPRIORITYR<n> characteristics are:

Purpose

Holds the priority of the corresponding interrupt.

Configuration

Some or all RW fields of this register have defined reset values.

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

The number of implemented GICD_IPRIORITYR<n> registers is 8*(GICD_TYPER.ITLinesNumber+1). Registers are numbered from 0.

GICD_IPRIORITYR0 to GICD_IPRIORITYR7 are Banked for each connected PE with GICR_TYPER.Processor_Number < 8.

Accessing GICD_IPRIORITYR0 to GICD_IPRIORITYR7 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_IPRIORITYR<n> is a 32-bit register.

Field descriptions

The GICD_IPRIORITYR<n> bit assignments are:

313029282726252423222120191817161514131211109876543210
Priority_offset_3BPriority_offset_2BPriority_offset_1BPriority_offset_0B

Priority_offset_3B, bits [31:24]

Interrupt priority value from an IMPLEMENTATION DEFINED range, at byte offset 3. Lower priority values correspond to greater priority of the interrupt.

This field resets to 0.

Priority_offset_2B, bits [23:16]

Interrupt priority value from an IMPLEMENTATION DEFINED range, at byte offset 2. Lower priority values correspond to greater priority of the interrupt.

This field resets to 0.

Priority_offset_1B, bits [15:8]

Interrupt priority value from an IMPLEMENTATION DEFINED range, at byte offset 1. Lower priority values correspond to greater priority of the interrupt.

This field resets to 0.

Priority_offset_0B, bits [7:0]

Interrupt priority value from an IMPLEMENTATION DEFINED range, at byte offset 0. Lower priority values correspond to greater priority of the interrupt.

This field resets to 0.

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

  • The corresponding GICD_IPRIORITYR<n> number, n, is given by n = m DIV 4.
  • The offset of the required GICD_IPRIORITYR<n> register is (0x400 + (4*n)).
  • The byte offset of the required Priority field in this register is m MOD 4, where:
    • Byte offset 0 refers to register bits [7:0].
    • Byte offset 1 refers to register bits [15:8].
    • Byte offset 2 refers to register bits [23:16].
    • Byte offset 3 refers to register bits [31:24].

Accessing the GICD_IPRIORITYR<n>

These registers are always used when affinity routing is not enabled. When affinity routing is enabled for the Security state of an interrupt:

  • GICR_IPRIORITYR<n> is used instead of GICD_IPRIORITYR<n> where n = 0 to 7 (that is, for SGIs and PPIs).
  • GICD_IPRIORITYR<n> is RAZ/WI where n = 0 to 7.

These registers are byte-accessible.

A register field corresponding to an unimplemented interrupt is RAZ/WI.

A GIC might implement fewer than eight priority bits, but must implement at least bits [7:4] of each field. In each field, unimplemented bits are RAZ/WI, see Interrupt prioritization.

When GICD_CTLR.DS==0:

  • A register bit that corresponds to a Group 0 or Secure Group 1 interrupt is RAZ/WI to Non-secure accesses.
  • A Non-secure access to a field that corresponds to a Non-secure Group 1 interrupt behaves as described in Software views of interrupt priority.

It is IMPLEMENTATION DEFINED whether changing the value of a priority field changes the priority of an active interrupt.

Note

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

ComponentOffsetInstance
GIC Distributor0x0400 + 4nGICD_IPRIORITYR<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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