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.
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.
CNTFRQ is a 32-bit register.
| 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 | |||||||||||||||||||||||||||||||
Clock frequency. Indicates the system counter clock frequency, in Hz.
The reset behavior of this field is:
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;