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

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:

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:

• 'Secure ICC_BPR1_EL1 Binary Point when CBPR == 0' in ARM® Generic Interrupt Controller Architecture Specification, GIC architecture version 3.0 and version 4.0 (ARM IHI 0069), for the processing of Group 1 interrupts in a GIC implementation that supports interrupt grouping, when GICC_CTLR.CBPR == 0.
• 'Non-secure ICC_BPR1_EL1 Binary Point when CBPR == 0' in ARM® Generic Interrupt Controller Architecture Specification, GIC architecture version 3.0 and version 4.0 (ARM IHI 0069), for all other cases.

This field resets to an architecturally UNKNOWN value.

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:

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.