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CNTV_CTL_EL0, Counter-timer Virtual Timer Control register

The CNTV_CTL_EL0 characteristics are:

Purpose

Control register for the virtual timer.

Configuration

AArch64 System register CNTV_CTL_EL0 bits [31:0] are architecturally mapped to AArch32 System register CNTV_CTL[31:0] .

RW fields in this register reset to architecturally UNKNOWN values.

Attributes

CNTV_CTL_EL0 is a 64-bit register.

Field descriptions

The CNTV_CTL_EL0 bit assignments are:

63	62	61	60	59	58	57	56	55	54	53	52	51	50	49	48	47	46	45	44	43	42	41	40	39	38	37	36	35	34	33	32
RES0
RES0																													ISTATUS	IMASK	ENABLE
31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0

Bits [63:3]

Reserved, RES0.

ISTATUS, bit [2]

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

ISTATUS	Meaning
0b0	Timer condition is not met.
0b1	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® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, chapter D6.

This bit is read-only.

IMASK, bit [1]

Timer interrupt mask bit. Permitted values are:

IMASK	Meaning
0b0	Timer interrupt is not masked by the IMASK bit.
0b1	Timer interrupt is masked by the IMASK bit.

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

This field resets to an architecturally UNKNOWN value.

ENABLE, bit [0]

Enables the timer. Permitted values are:

ENABLE	Meaning
0b0	Timer disabled.
0b1	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.

This field resets to an architecturally UNKNOWN value.

Accessing the CNTV_CTL_EL0

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.

Accesses to this register use the following encodings:

MRS <Xt>, CNTV_CTL_EL0

op0	op1	CRn	CRm	op2
0b11	0b011	0b1110	0b0011	0b001

if PSTATE.EL == EL0 then
    if !ELUsingAArch32(EL1) && !(EL2Enabled() && HCR_EL2.<E2H,TGE> == '11') && CNTKCTL_EL1.EL0VTEN == '0' then
        if EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TGE == '1' then
            AArch64.SystemAccessTrap(EL2, 0x18);
        else
            AArch64.SystemAccessTrap(EL1, 0x18);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.<E2H,TGE> == '11' && CNTHCTL_EL2.EL0VTEN == '0' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif !ELUsingAArch32(EL1) && !(EL2Enabled() && HCR_EL2.<E2H,TGE> == '11') && CNTHCTL_EL2.EL1TVT == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.<E2H,TGE> == '11' && SCR_EL3.NS == '0' then
        return CNTHVS_CTL_EL2;
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.<E2H,TGE> == '11' && SCR_EL3.NS == '1' then
        return CNTHV_CTL_EL2;
    else
        return CNTV_CTL_EL0;
elsif PSTATE.EL == EL1 then
    if !ELUsingAArch32(EL1) && !(EL2Enabled() && HCR_EL2.<E2H,TGE> == '11') && CNTHCTL_EL2.EL1TVT == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.<NV2,NV1,NV> == '111' then
        return NVMem[0x170];
    else
        return CNTV_CTL_EL0;
elsif PSTATE.EL == EL2 then
    if HCR_EL2.E2H == '1' && SCR_EL3.NS == '0' then
        return CNTHVS_CTL_EL2;
    elsif HCR_EL2.E2H == '1' && SCR_EL3.NS == '1' then
        return CNTHV_CTL_EL2;
    else
        return CNTV_CTL_EL0;
elsif PSTATE.EL == EL3 then
    return CNTV_CTL_EL0;

MSR CNTV_CTL_EL0, <Xt>

op0	op1	CRn	CRm	op2
0b11	0b011	0b1110	0b0011	0b001

if PSTATE.EL == EL0 then
    if !ELUsingAArch32(EL1) && !(EL2Enabled() && HCR_EL2.<E2H,TGE> == '11') && CNTKCTL_EL1.EL0VTEN == '0' then
        if EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TGE == '1' then
            AArch64.SystemAccessTrap(EL2, 0x18);
        else
            AArch64.SystemAccessTrap(EL1, 0x18);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.<E2H,TGE> == '11' && CNTHCTL_EL2.EL0VTEN == '0' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif !ELUsingAArch32(EL1) && !(EL2Enabled() && HCR_EL2.<E2H,TGE> == '11') && CNTHCTL_EL2.EL1TVT == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.<E2H,TGE> == '11' && SCR_EL3.NS == '0' then
        CNTHVS_CTL_EL2 = X[t];
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.<E2H,TGE> == '11' && SCR_EL3.NS == '1' then
        CNTHV_CTL_EL2 = X[t];
    else
        CNTV_CTL_EL0 = X[t];
elsif PSTATE.EL == EL1 then
    if !ELUsingAArch32(EL1) && !(EL2Enabled() && HCR_EL2.<E2H,TGE> == '11') && CNTHCTL_EL2.EL1TVT == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.<NV2,NV1,NV> == '111' then
        NVMem[0x170] = X[t];
    else
        CNTV_CTL_EL0 = X[t];
elsif PSTATE.EL == EL2 then
    if HCR_EL2.E2H == '1' && SCR_EL3.NS == '0' then
        CNTHVS_CTL_EL2 = X[t];
    elsif HCR_EL2.E2H == '1' && SCR_EL3.NS == '1' then
        CNTHV_CTL_EL2 = X[t];
    else
        CNTV_CTL_EL0 = X[t];
elsif PSTATE.EL == EL3 then
    CNTV_CTL_EL0 = X[t];

MRS <Xt>, CNTV_CTL_EL02

op0	op1	CRn	CRm	op2
0b11	0b101	0b1110	0b0011	0b001

if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && HCR_EL2.<NV2,NV1,NV> == '101' then
        if EL2Enabled() && HCR_EL2.<E2H,TGE> != '11' && CNTHCTL_EL2.EL1NVVCT == '1' then
            AArch64.SystemAccessTrap(EL2, 0x18);
        else
            return NVMem[0x170];
    elsif EL2Enabled() && HCR_EL2.NV == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    else
        UNDEFINED;
elsif PSTATE.EL == EL2 then
    if EL2Enabled() && HCR_EL2.E2H == '1' then
        return CNTV_CTL_EL0;
    else
        UNDEFINED;
elsif PSTATE.EL == EL3 then
    if EL2Enabled() && HCR_EL2.E2H == '1' then
        return CNTV_CTL_EL0;
    else
        UNDEFINED;

MSR CNTV_CTL_EL02, <Xt>

op0	op1	CRn	CRm	op2
0b11	0b101	0b1110	0b0011	0b001

if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && HCR_EL2.<NV2,NV1,NV> == '101' then
        if EL2Enabled() && HCR_EL2.<E2H,TGE> != '11' && CNTHCTL_EL2.EL1NVVCT == '1' then
            AArch64.SystemAccessTrap(EL2, 0x18);
        else
            NVMem[0x170] = X[t];
    elsif EL2Enabled() && HCR_EL2.NV == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    else
        UNDEFINED;
elsif PSTATE.EL == EL2 then
    if EL2Enabled() && HCR_EL2.E2H == '1' then
        CNTV_CTL_EL0 = X[t];
    else
        UNDEFINED;
elsif PSTATE.EL == EL3 then
    if EL2Enabled() && HCR_EL2.E2H == '1' then
        CNTV_CTL_EL0 = X[t];
    else
        UNDEFINED;

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