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CNTP_TVAL, Counter-timer Physical Timer TimerValue

The CNTP_TVAL characteristics are:

Purpose

Holds the timer value for the EL1 physical timer.

Configuration

The power domain of CNTP_TVAL 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

CNTP_TVAL is a 32-bit register.

Field descriptions

The CNTP_TVAL bit assignments are:

313029282726252423222120191817161514131211109876543210
TimerValue

TimerValue, bits [31:0]

The TimerValue view of the EL1 physical timer.

On a read of this register:

  • If CNTP_CTL.ENABLE is 0, the value returned is UNKNOWN.
  • If CNTP_CTL.ENABLE is 1, the value returned is (CompareValue - CNTPCT).

On a write of this register, CompareValue is set to (CNTPCT + TimerValue), where TimerValue is treated as a signed 32-bit integer.

When CNTP_CTL.ENABLE is 1, the timer condition is met when (CNTPCT - CompareValue) is greater than or equal to zero. This means that TimerValue acts like a 32-bit downcounter timer. When the timer condition is met:

  • CNTP_CTL.ISTATUS is set to 1.
  • If CNTP_CTL.IMASK is 0, an interrupt is generated.

When CNTP_CTL.ENABLE is 0, the timer condition is not met, but CNTPCT continues to count, so the TimerValue view appears to continue to count down.

This field resets to an architecturally UNKNOWN value.

Accessing the CNTP_TVAL

CNTP_TVAL can be implemented in any implemented CNTBaseN frame, 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:

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

For an implemented CNTEL0BaseN frame:

  • CNTP_TVAL is accessible in that frame if both:
    • CNTP_TVAL is accessible in the corresponding CNTBaseN frame:
    • The value of CNTEL0ACR.EL0PTEN is 1.
  • Otherwise, the CNTP_TVAL address in that frame is RAZ/WI.

CNTP_TVAL can be accessed through the memory-mapped interfaces:

ComponentFrameOffsetInstance
TimerCNTBaseN0x028CNTP_TVAL

Access on this interface is RW.

ComponentFrameOffsetInstance
TimerCNTEL0BaseN0x028CNTP_TVAL

Access on this interface is RW.



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