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CNTFRQ_EL0, Counter-timer Frequency register

The CNTFRQ_EL0 characteristics are:

Purpose

This register is provided so that software can discover the frequency of the system counter. It must be programmed with this value as part of system initialization. The value of the register is not interpreted by hardware.

Configuration

AArch64 System register CNTFRQ_EL0 bits [31:0] are architecturally mapped to AArch32 System register CNTFRQ[31:0] .

Attributes

CNTFRQ_EL0 is a 64-bit register.

Field descriptions

The CNTFRQ_EL0 bit assignments are:

6362616059585756555453525150494847464544434241403938373635343332
RES0
Clock frequency
313029282726252423222120191817161514131211109876543210

Bits [63:32]

Reserved, RES0.

Bits [31:0]

Clock frequency. Indicates the system counter clock frequency, in Hz.

On a Warm reset, this field resets to an architecturally UNKNOWN value.

Accessing the CNTFRQ_EL0

Accesses to this register use the following encodings:

MRS <Xt>, CNTFRQ_EL0

op0op1CRnCRmop2
0b110b0110b11100b00000b000
if PSTATE.EL == EL0 then
    if !(EL2Enabled() && HCR_EL2.<E2H,TGE> == '11') && CNTKCTL_EL1.<EL0PCTEN,EL0VCTEN> == '00' then
        if EL2Enabled() && HCR_EL2.TGE == '1' then
            AArch64.SystemAccessTrap(EL2, 0x18);
        else
            AArch64.SystemAccessTrap(EL1, 0x18);
    elsif EL2Enabled() && HCR_EL2.<E2H,TGE> == '11' && CNTHCTL_EL2.<EL0PCTEN,EL0VCTEN> == '00' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    else
        return CNTFRQ_EL0;
elsif PSTATE.EL == EL1 then
    return CNTFRQ_EL0;
elsif PSTATE.EL == EL2 then
    return CNTFRQ_EL0;
elsif PSTATE.EL == EL3 then
    return CNTFRQ_EL0;

MSR CNTFRQ_EL0, <Xt>

op0op1CRnCRmop2
0b110b0110b11100b00000b000
if IsHighestEL(PSTATE.EL) then
    CNTFRQ_EL0 = X[t];
else
    UNDEFINED;


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