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ISR, Interrupt Status Register

The ISR characteristics are:

Purpose

Shows the pending status of the IRQ, FIQ, or SError.

When executing at EL2, EL3, or Secure EL1, when SCR_EL3.EEL2 == 0b0, this shows the pending status of the physical interrupts.

When executing at Non-secure EL1, or at Secure EL1, when SCR_EL3.EEL2 == 0b01:

  • If the HCR.{IMO,FMO,AMO} bit has a value of 1, the corresponding ISR.{I,F,A} bit shows the pending status of the virtual IRQ, FIQ, or SError.
  • If the HCR.{IMO,FMO,AMO} bit has a value of 0, the corresponding ISR.{I,F,A} bit shows the pending status of the physical IRQ, FIQ, or SError.

Configuration

AArch32 System register ISR bits [31:0] are architecturally mapped to AArch64 System register ISR_EL1[31:0] .

Attributes

ISR is a 32-bit register.

Field descriptions

The ISR bit assignments are:

313029282726252423222120191817161514131211109876543210
RES0AIFRES0

Bits [31:9]

Reserved, RES0.

A, bit [8]

SError interrupt pending bit:

AMeaning
0b0

No pending SError interrupt.

0b1

An SError interrupt is pending.

If the SError interrupt is edge-triggered, this field is cleared to zero when the physical SError interrupt is taken.

I, bit [7]

IRQ pending bit. Indicates whether an IRQ interrupt is pending:

IMeaning
0b0

No pending IRQ.

0b1

An IRQ interrupt is pending.

F, bit [6]

FIQ pending bit. Indicates whether an FIQ interrupt is pending.

FMeaning
0b0

No pending FIQ.

0b1

An FIQ interrupt is pending.

Bits [5:0]

Reserved, RES0.

Accessing the ISR

Accesses to this register use the following encodings:

MRC{<c>}{<q>} <coproc>, {#}<opc1>, <Rt>, <CRn>, <CRm>{, {#}<opc2>}

coprocopc1CRnCRmopc2
0b11110b0000b11000b00010b000
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T12 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T12 == '1' then
        AArch32.TakeHypTrapException(0x03);
    else
        return ISR;
elsif PSTATE.EL == EL2 then
    return ISR;
elsif PSTATE.EL == EL3 then
    return ISR;
              


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