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OSLSR_EL1, OS Lock Status Register

The OSLSR_EL1 characteristics are:

Purpose

Provides the status of the OS Lock.

Configuration

AArch64 System register OSLSR_EL1 bits [31:0] are architecturally mapped to AArch32 System register DBGOSLSR[31:0] .

Attributes

OSLSR_EL1 is a 64-bit register.

Field descriptions

The OSLSR_EL1 bit assignments are:

6362616059585756555453525150494847464544434241403938373635343332
RES0
RES0OSLM[1]nTTOSLKOSLM[0]
313029282726252423222120191817161514131211109876543210

Bits [63:4]

Reserved, RES0.

OSLM, bits [3, 0]

OS lock model implemented. Identifies the form of OS save and restore mechanism implemented.

OSLMMeaning
0b00

OS Lock not implemented.

0b10

OS Lock implemented.

All other values are reserved. In an Armv8 implementation the value 0b00 is not permitted.

The OSLM field is split as follows:

  • OSLM[1] is OSLSR_EL1[3].
  • OSLM[0] is OSLSR_EL1[0].

nTT, bit [2]

Not 32-bit access. This bit is always RAZ. It indicates that a 32-bit access is needed to write the key to the OS Lock Access Register.

OSLK, bit [1]

OS Lock Status.

OSLKMeaning
0b0

OS Lock unlocked.

0b1

OS Lock locked.

The OS Lock is locked and unlocked by writing to the OS Lock Access Register.

On a Cold reset, this field resets to 1.

Accessing the OSLSR_EL1

Accesses to this register use the following encodings:

MRS <Xt>, OSLSR_EL1

op0op1CRnCRmop2
0b100b0000b00010b00010b100
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if Halted() && HaveEL(EL3) && EDSCR.SDD == '1' && boolean IMPLEMENTATION_DEFINED "EL3 trap priority when SDD == '1'" && MDCR_EL3.TDOSA == '1' then
        UNDEFINED;
    elsif EL2Enabled() && (!HaveEL(EL3) || SCR_EL3.FGTEn == '1') && HDFGRTR_EL2.OSLSR_EL1 == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif EL2Enabled() && MDCR_EL2.<TDE,TDOSA> != '00' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif HaveEL(EL3) && MDCR_EL3.TDOSA == '1' then
        if Halted() && EDSCR.SDD == '1' then
            UNDEFINED;
        else
            AArch64.SystemAccessTrap(EL3, 0x18);
    else
        return OSLSR_EL1;
elsif PSTATE.EL == EL2 then
    if Halted() && HaveEL(EL3) && EDSCR.SDD == '1' && boolean IMPLEMENTATION_DEFINED "EL3 trap priority when SDD == '1'" && MDCR_EL3.TDOSA == '1' then
        UNDEFINED;
    elsif HaveEL(EL3) && MDCR_EL3.TDOSA == '1' then
        if Halted() && EDSCR.SDD == '1' then
            UNDEFINED;
        else
            AArch64.SystemAccessTrap(EL3, 0x18);
    else
        return OSLSR_EL1;
elsif PSTATE.EL == EL3 then
    return OSLSR_EL1;