Virtual Counters

Versal ACAP Technical Reference Manual (AM011)

Document ID
AM011
Release Date
2022-04-26
Revision
1.4 English

Each APU core includes a virtual counter that indicates virtual time. The virtual counter contains the value of the physical counter minus a 64-bit virtual offset. When executing in a non-secure EL1 or EL0 mode, the virtual offset value relates to the current virtual machine. The CNTVOFF register contains the virtual offset. CNTVOFF is only accessible from EL2 or EL3 when SCR.NS is set to 1. The CNTVCT register holds the current virtual counter value.

Accessing the Virtual Counter

Software with sufficient privilege can read CNTVCT using a 64-bit system register read.

The virtual counter is accessible from secure and non-secure EL1 modes and from hypervisor mode. CNTKCTL.EL0VTEN determines whether the registers are accessible from EL0 modes. If an access is not permitted because CNTKCTL.EL0VTEN is set to 0, an attempted access from an EL0 is UNDEFINED.