CNTP_TVAL, Counter-timer Physical Timer TimerValue

The CNTP_TVAL characteristics are:

Purpose

Holds the timer value for the EL1 physical timer.

This register is part of the Generic Timer registers functional group.

Usage constraints

This register is accessible as follows:

Default
RW

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 ARMv8 ARM describes the status fields that identify whether a CNTBaseN frame is implemented, and for an implemented frame:

For an implemented CNTBaseN frame:

For an implemented CNTEL0BaseN frame:

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 ARMv8 ARM.

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:

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:

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.

Accessing the CNTP_TVAL

CNTP_TVAL can be accessed through its memory-mapped interface:

ComponentFrameOffset
TimerCNTBaseN 0x028
TimerCNTEL0BaseN 0x028



28/09/2017 08:24

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