CNTHV_TVAL, Counter-timer Virtual Timer TimerValue register (EL2)

The CNTHV_TVAL characteristics are:

Purpose

Provides AArch32 access to the timer value for the EL2 virtual timer.

Note

The EL2 virtual timer is implemented by ARMv8.1-VHE. It is only accessible from AArch32 state when EL0 is using AArch32, EL2 is using AArch64, and the value of HCR_EL2.{E2H, TGE} is {1, 1}.

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

Configuration

There is one instance of this register that is used in both Secure and Non-secure states.

AArch32 System register CNTHV_TVAL is architecturally mapped to AArch64 System register CNTHV_TVAL_EL2.

This register is introduced in ARMv8.1.

Attributes

CNTHV_TVAL is a 32-bit register.

Field descriptions

The CNTHV_TVAL bit assignments are:

313029282726252423222120191817161514131211109876543210
TimerValue

TimerValue, bits [31:0]

The TimerValue view of the EL2 virtual timer.

On a read of this register:

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

When CNTHV_CTL.ENABLE is 1, the timer condition is met when (CNTVCT - CNTHV_CVAL) 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 CNTV_CTL.ENABLE is 0, the timer condition is not met, but CNTVCT continues to count, so the TimerValue view appears to continue to count down.

Accessing the CNTHV_TVAL

This register can be read using MRC with the following syntax:

MRC <syntax>

This register can be written using MCR with the following syntax:

MCR <syntax>

This syntax uses the following encoding in the System instruction encoding space:

<syntax> opc1opc2CRncoprocCRm
p15, 0, <Rt>, c14, c3, 0000000111011110011

This register is accessed using the encoding for CNTV_TVAL.

Accessibility

The register is accessible as follows:

Control Accessibility
E2HTGENSEL0EL1EL2EL3
xx0 CNTV_TVAL CNTV_TVAL n/a CNTV_TVAL
001 CNTV_TVAL CNTV_TVAL CNTV_TVAL CNTV_TVAL
011 CNTV_TVAL n/a CNTV_TVAL CNTV_TVAL
101 CNTV_TVAL CNTV_TVAL n/a n/a
111RW n/a n/a n/a

This table applies to all instructions that can access this register.

Traps and enables

For a description of the prioritization of any generated exceptions, see section G1.11.2 (Exception priority order) in the ARM® Architecture Reference Manual, ARMv8, for ARMv8-A architecture profile for exceptions taken to AArch32 state, and section D1.13.2 (Synchronous exception prioritization) for exceptions taken to AArch64 state. Subject to the prioritization rules, the following traps and enables are applicable when accessing this register.

When EL2 is implemented and is using AArch64 and SCR_EL3.NS==1 && HCR_EL2.E2H==1 && HCR_EL2.TGE==1 :




28/09/2017 08:24

Copyright © 2010-2017 ARM Limited or its affiliates. All rights reserved. This document is Non-Confidential.