This read-only INTEGER reports the platform's current JTAG clock frequency in Hz, but is only measurable on a rev-3 control board; on rev-1 or rev-2 control boards it always returns 0 Hz. An administrator uses a nonzero reading to confirm the platform has a rev-3 control board capable of reporting this value at all. For example, seeing 0 Hz here on an otherwise healthy platform is expected and simply indicates an older control board revision, not a fault.