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GICC_BPR, CPU Interface Binary Point Register

The GICC_BPR characteristics are:

Purpose

Defines the point at which the priority value fields split into two parts, the group priority field and the subpriority field.

Configuration

RW fields in this register reset to architecturally UNKNOWN values.

In systems that support two Security states:

  • This register is Banked.
  • The Secure instance of this register determines Group 0 interrupt preemption.
  • The Non-secure instance of this register determines Group 1 interrupt preemption.

In systems that support only one Security state, when GICC_CTLR.CBPR == 0, this register determines only Group 0 interrupt preemption.

When GICC_CTLR.CBPR == 1, this register determines interrupt preemption for both Group 0 and Group 1 interrupts.

Attributes

GICC_BPR is a 32-bit register.

Field descriptions

The GICC_BPR bit assignments are:

313029282726252423222120191817161514131211109876543210
RES0Binary_Point

Bits [31:3]

Reserved, RES0.

Binary_Point, bits [2:0]

Controls how the 8-bit interrupt priority field is split into a group priority field, that determines interrupt preemption, and a subpriority field. The following list describes how this field determines the interrupt priority bits assigned to the group priority field:

  • Priority grouping for Group 1 interrupts when CBPR==0, for the processing of Group 1 interrupts in a GIC implementation that supports interrupt grouping, when GICC_CTLR.CBPR == 0.
  • Priority grouping for Group 0 interrupts, or Group 1 interrupts when CBPR==1, for all other cases.

This field resets to an architecturally UNKNOWN value.

Note

Aliasing the Non-secure GICC_BPR as GICC_ABPR in a multiprocessor system permits a PE that can make only Secure accesses to configure the preemption setting for Group 1 interrupts by accessing GICC_ABPR.

Accessing the GICC_BPR

This register is used only when System register access is not enabled. When System register access is enabled this register is RAZ/WI, and the System registers ICC_BPR0_EL1 and ICC_BPR1_EL1 provide equivalent functionality.

GICC_BPR can be accessed through the memory-mapped interfaces:

ComponentOffsetInstance
GIC CPU interface0x0008GICC_BPR

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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