CNTVCT

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CNTVCT_EL0, Counter-timer Virtual Count Register

Purpose

Reads of CNTVCT_EL0 return the 64-bit physical count value minus a virtual offset.

Configuration

AArch64 System register CNTVCT_EL0 bits [63:0] are architecturally mapped to AArch32 System register CNTVCT[63:0].

This register is present only when FEAT_AA64 is implemented. Otherwise, direct accesses to CNTVCT_EL0 are UNDEFINED.

All reads to the CNTVCT_EL0 occur in program order relative to reads to CNTVCTSS_EL0 or CNTVCT_EL0.

Attributes

Field descriptions

VirtualCount, bits [63:0]

Virtual count value.

When EL2 is implemented, if the access is not trapped, and any of the following are true, then reads of CNTVCT_EL0 from EL0 and EL1 return (PhysicalCountInt<63:0> - CNTVOFF_EL2<63:0>):

All of the following are true:
- The Effective value of HCR_EL2.{E2H, TGE} is not {1, 1}.
- CNTVCT_EL0 is read from EL0.
All of the following are true:
- The Effective value of HCR_EL2.E2H is 0.
- CNTVCT_EL0 is read from EL2.
CNTVCT_EL0 is read from EL1 or EL3.

Otherwise reads of CNTVCT_EL0 return PhysicalCountInt<63:0>.

PhysicalCountInt is defined by 'The Physical Counter'.

The reset behavior of this field is:

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

Accessing CNTVCT_EL0

Accesses to this register use the following encodings in the System register encoding space:

MRS <Xt>, CNTVCT_EL0

op0	op1	CRn	CRm	op2
0b11	0b011	0b1110	0b0000	0b010

if !IsFeatureImplemented(FEAT_AA64) then Undefined(); elsif PSTATE.EL == EL0 then if !ELIsInHost(EL0) && CNTKCTL_EL1().EL0VCTEN == '0' then if EL2Enabled() && HCR_EL2().TGE == '1' then AArch64_SystemAccessTrap(EL2, 0x18); else AArch64_SystemAccessTrap(EL1, 0x18); end; elsif ELIsInHost(EL0) && CNTHCTL_EL2().EL0VCTEN == '0' then AArch64_SystemAccessTrap(EL2, 0x18); elsif EL2Enabled() && !ELIsInHost(EL0) && CNTHCTL_EL2().EL1TVCT == '1' then AArch64_SystemAccessTrap(EL2, 0x18); else if HaveEL(EL2) && (!EL2Enabled() || !ELIsInHost(EL0)) then X{64}(t) = PhysicalCountInt() - CNTVOFF_EL2(); elsif HaveEL(EL2) && IsFeatureImplemented(FEAT_AA32EL2) && !ELUsingAArch32(EL2) && (!EL2Enabled() || !ELIsInHost(EL0)) then X{64}(t) = PhysicalCountInt() - CNTVOFF(); else X{64}(t) = PhysicalCountInt(); end; end; elsif PSTATE.EL == EL1 then if EL2Enabled() && CNTHCTL_EL2().EL1TVCT == '1' then AArch64_SystemAccessTrap(EL2, 0x18); else if HaveEL(EL2) then X{64}(t) = PhysicalCountInt() - CNTVOFF_EL2(); else X{64}(t) = PhysicalCountInt(); end; end; elsif PSTATE.EL == EL2 then if HaveEL(EL2) && !ELIsInHost(EL2) then X{64}(t) = PhysicalCountInt() - CNTVOFF_EL2(); else X{64}(t) = PhysicalCountInt(); end; elsif PSTATE.EL == EL3 then if HaveEL(EL2) && IsFeatureImplemented(FEAT_AA64EL2) && !ELUsingAArch32(EL2) then X{64}(t) = PhysicalCountInt() - CNTVOFF_EL2(); elsif HaveEL(EL2) && IsFeatureImplemented(FEAT_AA32EL2) then X{64}(t) = PhysicalCountInt() - CNTVOFF(); else X{64}(t) = PhysicalCountInt(); end; end;

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VirtualCount
VirtualCount