CNTFRQ

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. Otherwise, direct accesses to CNTFRQ are UNDEFINED.

Attributes

Field descriptions

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 PSTATE.EL == EL0 then if !ELUsingAArch32(EL1) && !ELIsInHost(EL0) && 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 ELIsInHost(EL0) && CNTHCTL_EL2.<EL0PCTEN,EL0VCTEN> == '00' then AArch64.AArch32SystemAccessTrap(EL2, 0x03); else R[t] = CNTFRQ; elsif PSTATE.EL == EL1 then R[t] = CNTFRQ; elsif PSTATE.EL == EL2 then R[t] = CNTFRQ; elsif PSTATE.EL == EL3 then R[t] = CNTFRQ;

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

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

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

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
Clock frequency

CNTFRQ, Counter-timer Frequency register