CNTFRQ, Counter-timer Frequency

The CNTFRQ characteristics are:

Purpose

This register is provided so that software can discover the frequency of the system counter. The instance of the register in the CNTCTLBase frame must be programmed with this value as part of system initialization. The value of the register is not interpreted by hardware.

Configuration

The power domain of CNTFRQ is IMPLEMENTATION DEFINED.

For more information see 'Power and reset domains for the system level implementation of the Generic Timer'.

Attributes

CNTFRQ is a 32-bit register.

Field descriptions

The CNTFRQ bit assignments are:

Bits [31:0]

Clock frequency. Indicates the system counter clock frequency, in Hz.

This field resets to an architecturally UNKNOWN value.

Accessing the CNTFRQ

CNTFRQ must be implemented as an RW register in the CNTCTLBase frame.

In a system that recognizes two Security states, the instance of the register in the CNTCTLBase frame is only accessible by Secure accesses.

CNTFRQ can be implemented as a RO register in any implemented CNTBaseN frame, and in the corresponding CNTEL0BaseN frame.

'CNTCTLBase status and control fields for the CNTBaseN and CNTEL0BaseN frames' describes the status fields that identify whether a CNTBaseN frame is implemented, and for an implemented frame:

• Whether the CNTBaseN frame has virtual timer capability.
• Whether the corresponding CNTEL0BaseN frame is implemented.
• For an implementation that recognizes two Security states, whether the CNTBaseN frame, and any corresponding CNTEL0BaseN frame, is accessible by Non-secure accesses.

For an implemented CNTBaseN frame:

• CNTFRQ is accessible in that frame, as a RO register, if the value of CNTACR<n>.RFRQ is 1.
• Otherwise, the CNTFRQ address in that frame is RAZ/WI.

For an implemented CNTEL0BaseN frame:

• CNTFRQ is accessible as a RO register in that frame if both:
  • CNTFRQ is accessible in the corresponding CNTBaseN frame.
  • Either the value of CNTEL0ACR.EL0VCTEN is 1 or the value of CNTEL0ACR.EL0PCTEN is 1.
• Otherwise, the CNTFRQ address in that frame is RAZ/WI.

CNTFRQ can be accessed through the memory-mapped interfaces:

Accesses on this interface are RO.

Accesses on this interface are RO.

Accesses on this interface are RO.