GICC_BPR: CPU Interface Binary Point Register

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

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.