ARM® Generic Interrupt Controller Architecture Specification: 4.4.3. Binary Point Register (ICCBPR)

4.4.3. Binary Point Register (ICCBPR)

The ICCBPR characteristics are:

Purpose

The register defines the point at which the priority value fields split into two parts, the group priority field and the subpriority field. The group priority field is used to determine interrupt preemption. For more information see Preemption and Priority grouping.

Usage constraints

The minimum binary point value is implementation defined in the range 0-3. An attempt to program the binary point field to a value less than the minimum value sets the field to the minimum value. On a reset, the binary point field is set to the minimum supported value.

Configurations

This register is available in all configurations of the GIC. If the GIC implements the Security Extensions:

This register is banked to provide Secure and Non-secure copies, see Register banking.
The Non-secure copy of the ICCBPR is aliased as the ICCABPR, see Aliased Binary Point Register (ICCABPR), so that a processor can use Secure accesses to access the Non-secure ICCBR.
The ICCICR.SBPR bit controls whether the Secure or Non-secure copy of the ICCBPR is used to determine the preemption of Non-secure interrupts, see CPU Interface Control Register (ICCICR).

Attributes

See the register summary in Table 4.2.

Figure 4.22 shows the ICCBPR bit assignments.

Figure 4.22. ICCBPR bit assignments

Table 4.28 shows the ICCBPR bit assignments.

Table 4.28. ICCBPR bit assignments

Bits	Name	Function
[31:3]	-	Reserved.
[2:0]	Binarypoint	The value of this field controls how the 8-bit interrupt priority field is split into a group priority field, used to determine interrupt preemption, and a subpriority field. For how this field determines the interrupt priority bits assigned to the group priority field see: Table 3.2, for a GIC that does not implement the Security Extensions, and for a GIC that implements the Security Extensions when processing a Secure interrupt Table 3.4, for a GIC that implements the Security Extensions when processing a Non-secure interrupt. See Priority grouping for more information.

Bits

Name

Function

[31:3]

Reserved.

[2:0]

Binarypoint

The value of this field controls how the 8-bit interrupt priority field is split into a group priority field, used to determine interrupt preemption, and a subpriority field. For how this field determines the interrupt priority bits assigned to the group priority field see:

Table 3.2, for a GIC that does not implement the Security Extensions, and for a GIC that implements the Security Extensions when processing a Secure interrupt
Table 3.4, for a GIC that implements the Security Extensions when processing a Non-secure interrupt.

See Priority grouping for more information.

Note

Aliasing the Non-secure ICCBPR as the ICCABPR means that, in a multiprocessor system, a processor that can make only Secure accesses to the GIC can access the Non-secure ICCBPR, to configure the preemption setting for Non-secure interrupts.

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