ICC_IAR1_EL1, Interrupt Controller Interrupt Acknowledge Register 1

The ICC_IAR1_EL1 characteristics are:

Purpose

The PE reads this register to obtain the INTID of the signaled Group 1 interrupt. This read acts as an acknowledge for the interrupt.

This register is part of:

Configuration

AArch64 System register ICC_IAR1_EL1 performs the same function as AArch32 System register ICC_IAR1.

To allow software to ensure appropriate observability of actions initiated by GIC register accesses, the PE and CPU interface logic must ensure that reads of this register are self-synchronising when interrupts are masked by the PE (that is when PSTATE.{I,F} == {0,0}). This ensures that the effect of activating an interrupt on the signaling of interrupt exceptions is observed when a read of this register is architecturally executed so that no spurious interrupt exception occurs if interrupts are unmasked by an instruction immediately following the read. See Observability of the effects of accesses to the GIC registers, for more information.

Attributes

ICC_IAR1_EL1 is a 32-bit register.

Field descriptions

The ICC_IAR1_EL1 bit assignments are:

313029282726252423222120191817161514131211109876543210
00000000INTID

Bits [31:24]

Reserved, RES0.

INTID, bits [23:0]

The INTID of the signaled interrupt.

This is the INTID of the highest priority pending interrupt, if that interrupt is of sufficient priority for it to be signaled to the PE, and if it can be acknowledged at the current Security state and Exception level.

If the highest priority pending interrupt is not observable, this field contains a special INTID to indicate the reason. These special INTIDs can be one of: 1020, 1021, or 1023. See Special INTIDs, for more information.

This field has either 16 or 24 bits implemented. The number of implemented bits can be found in ICC_CTLR_EL1.IDbits and ICC_CTLR_EL3.IDbits. If only 16 bits are implemented, bits [23:16] of this register are RES0.

Accessing the ICC_IAR1_EL1

This register can be read using MRS with the following syntax:

MRS <Xt>, <systemreg>

This syntax uses the following encoding in the System instruction encoding space:

<systemreg> op0op1CRnCRmop2
ICC_IAR1_EL11100011001100000

When HCR_EL2.IMO is set to 1, execution of this encoding at Non-secure EL1 results in an access to ICV_IAR1_EL1.

Accessibility

The register is accessible as follows:

Control Accessibility
FMOIMOTGENSEL0EL1EL2EL3
xxx0 - RO n/a RO
xx11 - n/a RORO
x001 - RORORO
x101 - ICV_IAR1_EL1 RORO

This table applies to all instructions that can access this register.

ICC_IAR1_EL1 is only accessible at Non-secure EL1 when HCR_EL2.IMO is set to 0.

Note

When HCR_EL2.IMO is set to 1, at Non-secure EL1, the instruction encoding used to access ICC_IAR1_EL1 results in an access to ICV_IAR1_EL1.

Traps and enables

For a description of the prioritization of any generated exceptions, see section D1.13.2 (Synchronous exception prioritization) in the ARM® Architecture Reference Manual, ARMv8, for ARMv8-A architecture profile. Subject to the prioritization rules, the following traps and enables are applicable when accessing this register.

In both Security states, and not dependent on other configuration bits:

When SCR_EL3.NS==1 :

When EL3 is implemented and is using AArch64 and SCR_EL3.NS==0 :

When EL3 is implemented and is using AArch64 :

When EL3 is implemented and is using AArch64 and SCR_EL3.NS==1 :




28/09/2017 08:24

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