ICH_AP0R<n>

AArch64 System register ICH_AP0R<n>_EL2 bits [31:0] are architecturally mapped to AArch32 System register ICH_AP0R<n>[31:0].

This register is present only when GICv3 is implemented and (EL2 is implemented or EL3 is implemented). Otherwise, direct accesses to ICH_AP0R<n>_EL2 are UNDEFINED.

This register has no effect if EL2 is not enabled in the current Security state.

Attributes

Field descriptions

Bits [63:32]

P<x>, bit [x], for x = 31 to 0

Provides the access to the virtual active priorities for Group 0 interrupts. Possible values of each bit are:

P<x>	Meaning
0b0	There is no Group 0 interrupt active with this priority level, or all active Group 0 interrupts with this priority level have undergone priority-drop.
0b1	There is a Group 0 interrupt active with this priority level which has not undergone priority drop.

The correspondence between priority levels and bits depends on the number of bits of priority that are implemented.

If 5 bits of preemption are implemented (bits [7:3] of priority), then there are 32 preemption levels, and the active state of these preemption levels are held in ICH_AP0R0_EL2 in the bits corresponding to Priority[7:3].

If 6 bits of preemption are implemented (bits [7:2] of priority), then there are 64 preemption levels, and:

The active state of preemption levels 0 - 124 are held in ICH_AP0R0_EL2 in the bits corresponding to 0:Priority[6:2].
The active state of preemption levels 128 - 252 are held in ICH_AP0R1_EL2 in the bits corresponding to 1:Priority[6:2].

If 7 bits of preemption are implemented (bits [7:1] of priority), then there are 128 preemption levels, and:

The active state of preemption levels 0 - 62 are held in ICH_AP0R0_EL2 in the bits corresponding to 00:Priority[5:1].
The active state of preemption levels 64 - 126 are held in ICH_AP0R1_EL2 in the bits corresponding to 01:Priority[5:1].
The active state of preemption levels 128 - 190 are held in ICH_AP0R2_EL2 in the bits corresponding to 10:Priority[5:1].
The active state of preemption levels 192 - 254 are held in ICH_AP0R3_EL2 in the bits corresponding to 11:Priority[5:1].

Note

Having the bit corresponding to a priority set to 1 in both ICH_AP0R<n>_EL2 and ICH_AP1R<n>_EL2 might result in UNPREDICTABLE behavior of the interrupt prioritization system for virtual interrupts.

The reset behavior of this field is:

On a Warm reset, this field resets to 0.

Additional information

Software must ensure that ICH_AP0R<n>_EL2 is 0 for legacy VMs otherwise behavior is UNPREDICTABLE. For more information about support for legacy VMs, see 'Support for legacy operation of VMs' in ARM® Generic Interrupt Controller Architecture Specification, GIC architecture version 3.0 and version 4.0 (ARM IHI 0069).

The active priorities for Group 0 and Group 1 interrupts for legacy VMs are held in ICH_AP1R<n>_EL2 and reads and writes to GICV_APR access ICH_AP1R<n>_EL2. This means that ICH_AP0R<n>_EL2 is inaccessible to legacy VMs.

Accessing ICH_AP0R<n>_EL2

ICH_AP0R1_EL2 is implemented only in implementations that support 6 or more bits of preemption. ICH_AP0R2_EL2 and ICH_AP0R3_EL2 are implemented only in implementations that support 7 bits of preemption. Unimplemented registers are UNDEFINED.

Note

The number of bits of preemption is indicated by ICH_VTR_EL2.PREbits

Writing to these registers with any value other than the last read value of the register (or 0x00000000 for a newly set up virtual machine) can result in UNPREDICTABLE behavior of the virtual interrupt prioritization system allowing either:

Virtual interrupts that should preempt execution to not preempt execution.
Interrupts that should not preempt execution to preempt execution at EL1 or EL0.

Writing to the active priority registers in any order other than the following order will result in UNPREDICTABLE behavior:

ICH_AP0R<n>_EL2.
ICH_AP1R<n>_EL2.

Having the bit corresponding to a priority set in both ICH_AP0R<n>_EL2 and ICH_AP1R<n>_EL2 can result in UNPREDICTABLE behavior of the interrupt prioritization system for virtual interrupts.

Accesses to this register use the following encodings in the System register encoding space:

MRS <Xt>, ICH_AP0R<m>_EL2 ; Where m = 0-3

op0	op1	CRn	CRm	op2
0b11	0b100	0b1100	0b1000	0b0:m[1:0]

integer m = UInt(op2<1:0>); if m == 1 && NUM_GIC_PREEMPTION_BITS < 6 then UNDEFINED; elsif (m == 2 || m == 3) && NUM_GIC_PREEMPTION_BITS < 7 then UNDEFINED; elsif PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EffectiveHCR_EL2_NVx() IN {'1x1'} then X[t, 64] = NVMem[0x480 + (8 * m)]; elsif EffectiveHCR_EL2_NVx() IN {'xx1'} then AArch64.SystemAccessTrap(EL2, 0x18); else UNDEFINED; elsif PSTATE.EL == EL2 then if ICC_SRE_EL2.SRE == '0' then AArch64.SystemAccessTrap(EL2, 0x18); else X[t, 64] = ICH_AP0R_EL2[m]; elsif PSTATE.EL == EL3 then if ICC_SRE_EL3.SRE == '0' then AArch64.SystemAccessTrap(EL3, 0x18); else X[t, 64] = ICH_AP0R_EL2[m];

MSR ICH_AP0R<m>_EL2, <Xt> ; Where m = 0-3

op0	op1	CRn	CRm	op2
0b11	0b100	0b1100	0b1000	0b0:m[1:0]

integer m = UInt(op2<1:0>); if m == 1 && NUM_GIC_PREEMPTION_BITS < 6 then UNDEFINED; elsif (m == 2 || m == 3) && NUM_GIC_PREEMPTION_BITS < 7 then UNDEFINED; elsif PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EffectiveHCR_EL2_NVx() IN {'1x1'} then NVMem[0x480 + (8 * m)] = X[t, 64]; elsif EffectiveHCR_EL2_NVx() IN {'xx1'} then AArch64.SystemAccessTrap(EL2, 0x18); else UNDEFINED; elsif PSTATE.EL == EL2 then if ICC_SRE_EL2.SRE == '0' then AArch64.SystemAccessTrap(EL2, 0x18); else ICH_AP0R_EL2[m] = X[t, 64]; elsif PSTATE.EL == EL3 then if ICC_SRE_EL3.SRE == '0' then AArch64.SystemAccessTrap(EL3, 0x18); else ICH_AP0R_EL2[m] = X[t, 64];

63	62	61	60	59	58	57	56	55	54	53	52	51	50	49	48	47	46	45	44	43	42	41	40	39	38	37	36	35	34	33	32
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
P31	P30	P29	P28	P27	P26	P25	P24	P23	P22	P21	P20	P19	P18	P17	P16	P15	P14	P13	P12	P11	P10	P9	P8	P7	P6	P5	P4	P3	P2	P1	P0

ICH_AP0R<n>_EL2, Interrupt Controller Hyp Active Priorities Group 0 Registers, n = 0 - 3

Purpose

Configuration