GICH_HCR, Hypervisor Control Register
The GICH_HCR characteristics are:
Purpose
Controls the virtual CPU interface.
Configuration
This register is available when the GIC implementation supports interrupt virtualization.
Attributes
GICH_HCR is a 32-bit register.
Field descriptions
The GICH_HCR bit assignments are:
| 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 |
| EOICount | RES0 | VGrp1DIE | VGrp1EIE | VGrp0DIE | VGrp0EIE | NPIE | LRENPIE | UIE | En | ||||||||||||||||||||||
EOICount, bits [31:27]
Counts the number of EOIs received that do not have a corresponding entry in the List registers. The virtual CPU interface increments this field automatically when a matching EOI is received. EOIs that do not clear a bit in GICH_APR<n> do not cause an increment. If an EOI occurs when the value of this field is 31, then the field wraps to 0.
The maintenance interrupt is asserted whenever this field is nonzero and GICH_HCR.LRENPIE == 1.
On a Warm reset, this field resets to an architecturally UNKNOWN value.
Bits [26:8]
Reserved, RES0.
VGrp1DIE, bit [7]
VM Group 1 Disabled Interrupt Enable.
Enables the signaling of a maintenance interrupt while signaling of Group 1 interrupts from the virtual CPU interface to the connected virtual machine is disabled:
| VGrp1DIE | Meaning |
|---|---|
| 0b0 |
Maintenance interrupt disabled. |
| 0b1 |
Maintenance interrupt signaled when GICV_CTLR.EnableGrp1 == 0. |
On a Warm reset, this field resets to an architecturally UNKNOWN value.
VGrp1EIE, bit [6]
VM Group 1 Enabled Interrupt Enable.
Enables the signaling of a maintenance interrupt while signaling of Group 1 interrupts from the virtual CPU interface to the connected virtual machine is enabled:
| VGrp1EIE | Meaning |
|---|---|
| 0b0 |
Maintenance interrupt disabled. |
| 0b1 |
Maintenance interrupt signaled when GICV_CTLR.EnableGrp1 == 1. |
On a Warm reset, this field resets to an architecturally UNKNOWN value.
VGrp0DIE, bit [5]
VM Group 0 Disabled Interrupt Enable.
Enables the signaling of a maintenance interrupt while signaling of Group 0 interrupts from the virtual CPU interface to the connected virtual machine is disabled:
| VGrp0DIE | Meaning |
|---|---|
| 0b0 |
Maintenance interrupt disabled. |
| 0b1 |
Maintenance interrupt signaled when GICV_CTLR.EnableGrp0 == 0. |
On a Warm reset, this field resets to an architecturally UNKNOWN value.
VGrp0EIE, bit [4]
VM Group 0 Enabled Interrupt Enable.
Enables the signaling of a maintenance interrupt while signaling of Group 0 interrupts from the virtual CPU interface to the connected virtual machine is enabled:
| VGrp0EIE | Meaning |
|---|---|
| 0b0 |
Maintenance interrupt disabled. |
| 0b1 |
Maintenance interrupt signaled when GICV_CTLR.EnableGrp0 == 1. |
On a Warm reset, this field resets to an architecturally UNKNOWN value.
NPIE, bit [3]
No Pending Interrupt Enable.
Enables the signaling of a maintenance interrupt while no pending interrupts are present in the List registers:
| NPIE | Meaning |
|---|---|
| 0b0 |
Maintenance interrupt disabled. |
| 0b1 |
Maintenance interrupt signaled while the List registers contain no interrupts in the pending state. |
On a Warm reset, this field resets to an architecturally UNKNOWN value.
LRENPIE, bit [2]
List Register Entry Not Present Interrupt Enable.
Enables the signaling of a maintenance interrupt while the virtual CPU interface does not have a corresponding valid List register for an EOI request:
| LRENPIE | Meaning |
|---|---|
| 0b0 |
Maintenance interrupt disabled. |
| 0b1 |
Maintenance interrupt signaled while GICH_HCR.EOICount is not 0. |
On a Warm reset, this field resets to an architecturally UNKNOWN value.
UIE, bit [1]
Underflow Interrupt Enable.
Enables the signaling of a maintenance interrupt when the List registers are either empty or hold only one valid entry.
| UIE | Meaning |
|---|---|
| 0b0 |
Maintenance interrupt disabled. |
| 0b1 |
A maintenance interrupt is signaled if zero or one of the List register entries are marked as a valid interrupt. |
On a Warm reset, this field resets to an architecturally UNKNOWN value.
En, bit [0]
Enable.
Global enable bit for the virtual CPU interface.
| En | Meaning |
|---|---|
| 0b0 |
Virtual CPU interface operation is disabled. |
| 0b1 |
Virtual CPU interface operation is enabled. |
When this field is 0:
- The virtual CPU interface does not signal any maintenance interrupts.
- The virtual CPU interface does not signal any virtual interrupts.
- A read of GICV_IAR or GICV_AIAR returns a spurious interrupt ID.
On a Warm reset, this field resets to an architecturally UNKNOWN value.
The VGrp1DIE, VGrp1EIE, VGrp0DIE, and VGrp0EIE fields permit the hypervisor to track the virtual CPU interfaces that are enabled. The hypervisor can then route interrupts that have multiple targets correctly and efficiently, without having to read the virtual CPU interface status.
See 'Maintenance interrupts' in ARM® Generic Interrupt Controller Architecture Specification, GIC architecture version 3.0 and version 4.0 (ARM IHI 0069) and GICH_MISR for more information.
Accessing the GICH_HCR
This register is used only when System register access is not enabled. When System register access is enabled:
- For AArch32 implementations, ICH_HCR provides equivalent functionality.
- For AArch64 implementations, ICH_HCR_EL2 provides equivalent functionality.
GICH_HCR.En must be set to 1 for any virtual or maintenance interrupt to be asserted.
GICH_HCR can be accessed through the memory-mapped interfaces:
| Component | Offset | Instance |
|---|---|---|
| GIC Virtual interface control | 0x0000 | GICH_HCR |
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.