CNTFRQ, Counter-timer Frequency register

The CNTFRQ 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

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

This register is present only when AArch32 is supported at any Exception level. Otherwise, direct accesses to CNTFRQ are UNDEFINED.

Attributes

CNTFRQ is a 32-bit register.

Field descriptions

The CNTFRQ bit assignments are:

313029282726252423222120191817161514131211109876543210
Clock frequency

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

Accesses to this register use the following encodings:

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

coprocopc1CRnCRmopc2
0b11110b0000b11100b00000b000

if PSTATE.EL == EL0 then if !ELUsingAArch32(EL1) && !(EL2Enabled() && HCR_EL2.<E2H,TGE> == '11') && CNTKCTL_EL1.<EL0PCTEN,EL0VCTEN> == '00' then if EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TGE == '1' then AArch64.AArch32SystemAccessTrap(EL2, 0x03); else AArch64.AArch32SystemAccessTrap(EL1, 0x03); elsif ELUsingAArch32(EL1) && CNTKCTL.PL0PCTEN == '0' && CNTKCTL.PL0VCTEN == '0' then if EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TGE == '1' then AArch64.AArch32SystemAccessTrap(EL2, 0x03); elsif EL2Enabled() && ELUsingAArch32(EL2) && HCR.TGE == '1' then AArch32.TakeHypTrapException(0x00); else UNDEFINED; elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.<E2H,TGE> == '11' && CNTHCTL_EL2.<EL0PCTEN,EL0VCTEN> == '00' then AArch64.AArch32SystemAccessTrap(EL2, 0x03); else return CNTFRQ; elsif PSTATE.EL == EL1 then return CNTFRQ; elsif PSTATE.EL == EL2 then return CNTFRQ; elsif PSTATE.EL == EL3 then return CNTFRQ;

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

coprocopc1CRnCRmopc2
0b11110b0000b11100b00000b000

if IsHighestEL(PSTATE.EL) then CNTFRQ = R[t]; else UNDEFINED;




30/09/2020 15:07; ccead0cb9f089f9ceec50268e82aec9e71047211

Copyright © 2010-2020 Arm Limited or its affiliates. All rights reserved. This document is Non-Confidential.