CNTV_CTL_EL0, Counter-timer Virtual Timer Control register

The CNTV_CTL_EL0 characteristics are:

Purpose

Control register for the virtual timer.

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

Configuration

AArch64 System register CNTV_CTL_EL0 is architecturally mapped to AArch32 System register CNTV_CTL.

RW fields in this register reset to architecturally UNKNOWN values.

Attributes

CNTV_CTL_EL0 is a 32-bit register.

Field descriptions

The CNTV_CTL_EL0 bit assignments are:

313029282726252423222120191817161514131211109876543210
00000000000000000000000000000ISTATUSIMASKENABLE

Bits [31:3]

Reserved, RES0.

ISTATUS, bit [2]

The status of the timer. This bit indicates whether the timer condition is met:

ISTATUSMeaning
0

Timer condition is not met.

1

Timer condition is met.

When the value of the ENABLE bit is 1, ISTATUS indicates whether the timer condition is met. ISTATUS takes no account of the value of the IMASK bit. If the value of ISTATUS is 1 and the value of IMASK is 0 then the timer interrupt is asserted.

When the value of the ENABLE bit is 0, the ISTATUS field is UNKNOWN.

For more information see 'Operation of the CompareValue views of the timers' and 'Operation of the TimerValue views of the timers' in the ARM ARM, chapter D6.

This bit is read-only.

IMASK, bit [1]

Timer interrupt mask bit. Permitted values are:

IMASKMeaning
0

Timer interrupt is not masked by the IMASK bit.

1

Timer interrupt is masked by the IMASK bit.

For more information, see the description of the ISTATUS bit.

ENABLE, bit [0]

Enables the timer. Permitted values are:

ENABLEMeaning
0

Timer disabled.

1

Timer enabled.

Setting this bit to 0 disables the timer output signal, but the timer value accessible from CNTV_TVAL_EL0 continues to count down.

Note

Disabling the output signal might be a power-saving option.

Accessing the CNTV_CTL_EL0

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

MRS <Xt>, <systemreg>

This register can be written using MSR (register) with the following syntax:

MSR <systemreg>, <Xt>

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

<systemreg> op0op1CRnCRmop2
CNTV_CTL_EL01101111100011001
CNTV_CTL_EL021110111100011001

Accessibility

The register is accessible as follows:

<systemreg> Control Accessibility
E2HTGENSEL0EL1EL2EL3
CNTV_CTL_EL0xx0RWRW n/a RW
CNTV_CTL_EL0001RWRWRWRW
CNTV_CTL_EL0011RW n/a RWRW
CNTV_CTL_EL0101RWRW CNTHV_CTL_EL2 RW
CNTV_CTL_EL0111 CNTHV_CTL_EL2 n/a CNTHV_CTL_EL2 RW
CNTV_CTL_EL02xx0 - - n/a -
CNTV_CTL_EL02001 - - - -
CNTV_CTL_EL02011 - n/a - -
CNTV_CTL_EL02101 - - RWRW
CNTV_CTL_EL02111 - n/a RWRW

When HCR_EL2.E2H is 1, without explicit synchronization, access from EL3 using the mnemonic CNTV_CTL_EL0 or CNTV_CTL_EL02 are not guaranteed to be ordered with respect to accesses using the other mnemonic.

Traps and enables

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

When HCR_EL2.E2H==0 :

When EL2 is implemented and is using AArch64 and SCR_EL3.NS==1 && HCR_EL2.E2H==1 && HCR_EL2.TGE==0 :

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




02/05/2017 15:43

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