Architectural clock gating modes
When the Cortex®‑A77 core is in standby mode, it is architecturally clock gated at the top of the clock tree.
Wait for Interrupt (WFI) and Wait for Event (WFE) are features of Arm®v8‑A architecture that put the core in a low-power standby mode by architecturally disabling the clock at the top of the clock tree. The core is fully powered and retains all the state in standby mode.
There is a small dynamic power overhead from the logic that is required to wake up the core from WFI low-power state. Other than this, the power that is drawn is reduced to static leakage current only.