11.4.3 ACT Update Disable
When Active Clock Tuning is enabled, the OSCTUNE register is
                                    continuously updated every ACT clock cycle. The ACT Update
                                    Disable (ACTUD) bit can be used to
                                    suspend updates to the OSCTUNE register. When ACTUD is set
                                    (ACTUD = 1), updates to OSCTUNE are suspended,
                                    although the module continues to operate. The last value written
                                    to OSCTUNE is used for tuning, and the ACTLOCK bit is continually
                                    updated for each ACT cycle. When ACTUD is clear (ACTUD =
                                                0), the module updates OSCTUNE
                                    register every ACT cycle.
