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CNTV_CVAL, Counter-timer Virtual Timer CompareValue

The CNTV_CVAL characteristics are:

Purpose

Holds the 64-bit compare value for the virtual timer.

Configuration

The power domain of CNTV_CVAL is IMPLEMENTATION DEFINED.

On a reset of the reset domain in which an RW instance of this register is implemented, RW fields in the register reset to UNKNOWN values. The register is not affected by a reset of any other reset domain. For more information see 'Power and reset domains for the system level implementation of the Generic Timer' in Chapter I1 of the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile.

Attributes

CNTV_CVAL is a 64-bit register.

Field descriptions

The CNTV_CVAL bit assignments are:

6362616059585756555453525150494847464544434241403938373635343332
CompareValue
CompareValue
313029282726252423222120191817161514131211109876543210

CompareValue, bits [63:0]

Holds the virtual timer CompareValue.

When CNTV_CTL.ENABLE is 1, the timer condition is met when (CNTVCT - CompareValue) is greater than or equal to zero. This means that CompareValue acts like a 64-bit upcounter timer. When the timer condition is met:

  • CNTV_CTL.ISTATUS is set to 1.
  • An interrupt is generated if CNTV_CTL.IMASK is 0.

When CNTV_CTL.ENABLE is 0, the timer condition is not met, but CNTVCT continues to count.

This field resets to an architecturally UNKNOWN value.

Accessing the CNTV_CVAL

CNTV_CVAL can be implemented in any implemented CNTBaseN frame that has virtual timer capability, and in the corresponding CNTEL0BaseN frame.

'CNTCTLBase status and control fields for the CNTBaseN and CNTEL0BaseN frames' in Chapter I1 of the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile describes the status fields that identify whether a CNTBaseN frame is implemented, and for an implemented frame:

  • Whether the CNTBaseN frame has virtual timer capability.
  • Whether the corresponding CNTEL0BaseN frame is implemented.
  • For an implementation that recognizes two Security states, whether the CNTBaseN frame, and any corresponding CNTEL0BaseN frame, is accessible by Non-secure accesses.

For an implemented CNTBaseN frame that has virtual timer capability:

  • CNTV_CVAL is accessible in that frame if the value of CNTACR<n>.RWVT is 1.
  • Otherwise, the CNTV_CVAL address in that frame is RAZ/WI.

For an implemented CNTEL0BaseN frame:

  • CNTV_CVAL is accessible in that frame if both:
    • CNTV_CVAL is accessible in the corresponding CNTBaseN frame:
    • The value of CNTEL0ACR.EL0VTEN is 1.
  • Otherwise, the CNTV_CVAL address in that frame is RAZ/WI.

If the implementation supports 64-bit atomic accesses, then the CNTV_CVAL register must be accessible as an atomic 64-bit value.

CNTV_CVAL can be accessed through the memory-mapped interfaces:

ComponentFrameOffsetInstanceRange
TimerCNTBaseN0x030CNTV_CVAL31:0

Access on this interface is RW.

ComponentFrameOffsetInstanceRange
TimerCNTBaseN0x034CNTV_CVAL63:32

Access on this interface is RW.

ComponentFrameOffsetInstanceRange
TimerCNTEL0BaseN0x030CNTV_CVAL31:0

Access on this interface is RW.

ComponentFrameOffsetInstanceRange
TimerCNTEL0BaseN0x034CNTV_CVAL63:32

Access on this interface is RW.



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