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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

This register is present only when FEAT_GICv3_LEGACY is implemented. Otherwise, direct accesses to GICC_BPR are RES0.

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

31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0
RES0 | Binary_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:

- '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.

The reset behavior of this field is:

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

#### Additional information

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 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:

Component | Offset | Instance
--- | --- | ---
GIC CPU interface | 0x0008 | GICC_BPR

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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26/03/2024 09:49; 67c0ae5282a7629ba0ea0ba7267b43cd4f7939f6

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