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PMVIDSR, VMID Sample Register

The PMVIDSR characteristics are:


Contains the sampled VMID value that is captured on reading PMPCSR[31:0].


PMVIDSR is in the Core power domain.

This register is present only when FEAT_PCSRv8p2 is implemented and EL2 is implemented. Otherwise, direct accesses to PMVIDSR are RES0.


Before Armv8.2, the PC Sample-based Profiling Extension can be implemented in the external debug register space, as indicated by the value of EDDEVID.PCSample.


PMVIDSR is a 32-bit register.

Field descriptions

The PMVIDSR bit assignments are:


Bits [31:16]

Reserved, RES0.

VMID[15:8], bits [15:8]

When FEAT_VMID16 is implemented:

Extension to VMID[7:0]. See VMID[7:0] for more details.

On a Cold reset, this field resets to an architecturally UNKNOWN value.


Reserved, RES0.

VMID, bits [7:0]

VMID sample. The VMID associated with the most recent PMPCSR sample. When the most recent PMPCSR sample was generated:

  • This field is set to an UNKNOWN value if any of the following apply:
    • EL2 is disabled in the current Security state.
    • The PE is executing at EL2.
    • EL2 is enabled in the current Security state, the PE is executing at EL0, EL2 is using AArch64, HCR_EL2.E2H == 1, and HCR_EL2.TGE == 1.
  • Otherwise:
    • If EL2 is using AArch64 and either FEAT_VMID16 is not implemented or VTCR_EL2.VS is 1, this field is set to VTTBR_EL2.VMID.
    • If EL2 is using AArch64, FEAT_VMID16 is implemented, and VTCR_EL2.VS is 0, PMVIDSR.VMID[7:0] is set to VTTBR_EL2.VMID[7:0] and PMVIDSR.VMID[15:8] is RES0.
    • If EL2 is using AArch32, this field is set to VTTBR.VMID.

Because the value written to PMVIDR is an indirect read of the VMID value, it is CONSTRAINED UNPREDICTABLE whether PMVIDSR is set to the original or new value if PMPCSR samples:

  • An instruction that writes to the VMID value.
  • The next Context synchronization event.
  • Any instruction executed between these two instructions.

On a Cold reset, this field resets to an architecturally UNKNOWN value.

Accessing the PMVIDSR

IMPLEMENTATION DEFINED extensions to external debug might make the value of this register UNKNOWN, see 'Permitted behavior that might make the PC Sample-based profiling registers UNKNOWN'.

PMVIDSR can be accessed through the external debug interface:


This interface is accessible as follows:

  • When IsCorePowered(), !DoubleLockStatus() and !OSLockStatus() accesses to this register are RO.
  • Otherwise accesses to this register generate an error response.