CNTFRQ

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CNTFRQ, Counter-timer Frequency register

Purpose

This register is provided so that software can discover the effective 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

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

This register is present only when FEAT_AA32 is implemented. Otherwise, direct accesses to CNTFRQ are UNDEFINED.

Attributes

Field descriptions

ClockFreq, bits [31:0]

Accessing CNTFRQ

Accesses to this register use the following encodings in the System register encoding space:

MRC{<c>}{<q>} <coproc>, {#}<opc1>, <Rt>, <CRn>, <CRm>{, {#}<opc2>}

coproc	opc1	CRn	CRm	opc2
0b1111	0b000	0b1110	0b0000	0b000

if !IsFeatureImplemented(FEAT_AA32) then Undefined(); elsif PSTATE.EL == EL0 then if IsFeatureImplemented(FEAT_AA64EL1) && !ELUsingAArch32(EL1) && !ELIsInHost(EL0) && CNTKCTL_EL1().[EL0PCTEN,EL0VCTEN] == '00' then if EL2Enabled() && (IsFeatureImplemented(FEAT_AA64EL2) && !ELUsingAArch32(EL2)) && HCR_EL2().TGE == '1' then AArch64_AArch32SystemAccessTrap(EL2, 0x03); else AArch64_AArch32SystemAccessTrap(EL1, 0x03); end; elsif IsFeatureImplemented(FEAT_AA32EL1) && ELUsingAArch32(EL1) && CNTKCTL().PL0PCTEN == '0' && CNTKCTL().PL0VCTEN == '0' then if EL2Enabled() && (IsFeatureImplemented(FEAT_AA64EL2) && !ELUsingAArch32(EL2)) && HCR_EL2().TGE == '1' then AArch64_AArch32SystemAccessTrap(EL2, 0x03); elsif EL2Enabled() && (IsFeatureImplemented(FEAT_AA32EL2) && ELUsingAArch32(EL2)) && HCR().TGE == '1' then AArch32_TakeHypTrapException(0x00); else Undefined(); end; elsif ELIsInHost(EL0) && (IsFeatureImplemented(FEAT_AA64EL2) && !ELUsingAArch32(EL2)) && CNTHCTL_EL2().[EL0PCTEN,EL0VCTEN] == '00' then AArch64_AArch32SystemAccessTrap(EL2, 0x03); else R(t) = CNTFRQ(); end; elsif PSTATE.EL == EL1 then R(t) = CNTFRQ(); elsif PSTATE.EL == EL2 then R(t) = CNTFRQ(); elsif PSTATE.EL == EL3 then R(t) = CNTFRQ(); end;

MCR{<c>}{<q>} <coproc>, {#}<opc1>, <Rt>, <CRn>, <CRm>{, {#}<opc2>}

coproc	opc1	CRn	CRm	opc2
0b1111	0b000	0b1110	0b0000	0b000

if !IsFeatureImplemented(FEAT_AA32) then Undefined(); elsif IsHighestEL(PSTATE.EL) then CNTFRQ() = R(t); else Undefined(); end;

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ClockFreq