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] .
RW fields in this register reset to architecturally UNKNOWN values.
Attributes
CNTFRQ is a 32-bit register.
Field descriptions
The CNTFRQ bit assignments are:
| 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 | |||||||||||||||||||||||||||||||
Bits [31:0]
Clock frequency. Indicates the system counter clock frequency, in Hz.
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>}
| coproc | opc1 | CRn | CRm | opc2 |
|---|---|---|---|---|
| 0b1111 | 0b000 | 0b1110 | 0b0000 | 0b000 |
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>}
| coproc | opc1 | CRn | CRm | opc2 |
|---|---|---|---|---|
| 0b1111 | 0b000 | 0b1110 | 0b0000 | 0b000 |
if IsHighestEL(PSTATE.EL) then
CNTFRQ = R[t];
else
UNDEFINED;