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OSLAR_EL1

OSLAR_EL1, OS Lock Access Register

The OSLAR_EL1 characteristics are:

Purpose

Used to lock or unlock the OS Lock.

Configuration

External register OSLAR_EL1 bits [31:0] are architecturally mapped to AArch64 System register OSLAR_EL1[31:0].

OSLAR_EL1 is in the Core power domain.

The OS Lock can also be locked or unlocked using DBGOSLAR.

If FEAT_Debugv8p2 is not implemented, it is IMPLEMENTATION DEFINED whether external debug accesses to OSLAR_EL1 are ignored and return an error when AllowExternalDebugAccess() returns FALSE for the access.

If FEAT_Debugv8p2 is implemented, external debug accesses to OSLAR_EL1 are ignored and return an error when AllowExternalDebugAccess() returns FALSE for the access.

Attributes

OSLAR_EL1 is a 32-bit register.

Field descriptions

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																															OSLK

Bits [31:1]

Reserved, RES0.

OSLK, bit [0]

On writes to OSLAR_EL1, bit[0] is copied to the OS Lock.

Use EDPRSR.OSLK to check the current status of the lock.

Accessing OSLAR_EL1

Note

SoftwareLockStatus() depends on the type of access attempted and AllowExternalDebugAccess() has a new definition from Armv8.4. Refer to the Pseudocode definitions for more information.

OSLAR_EL1 can be accessed through the external debug interface:

Component	Offset	Instance
Debug	0x300	OSLAR_EL1

Accessible as follows:

When DoubleLockStatus(), or !IsCorePowered(), or (!AllowExternalDebugAccess(addrdesc) and FEAT_Debugv8p2 is implemented), accesses to this register generate an error response.
When AllowExternalDebugAccess(addrdesc) and SoftwareLockStatus(), accesses to this register are WI.
When AllowExternalDebugAccess(addrdesc) and !SoftwareLockStatus(), accesses to this register are WO.
Otherwise, accesses to this register are IMPDEF.

2026-03-12 12:23:09, 2025-09_rel_asl1