Synchronization and Recalculation of Timed Power On timestamps in an LPAR system with a virtualized clock
Original Publication Date: 2002-Nov-20
Included in the Prior Art Database: 2002-Nov-20
Described is a method to synchronize the RTC (Real Time Clock) and WDT ( Watch Dog Timer) on a Logical Partitioned (LPAR) system with a virtual Time Of Day (TOD) subsystem, that supports Timed Power On (TPO) functionality. If the limitations of this system are one physical battery-backed RTC and one WDT present, it is required that the WDT and RTC are synchronized to obtain the expected results. This is to power on the system at a specific TPO Time/Date set by the user. The LPAR implementation of virtual TOD allows each LPAR partition to maintain its own private time and to assume that it is in full control of the RTC and WDT. It is required that the RTC and WDT are synchronized specially on situations when the partition issuing a TPO command is in a different TOD state than the master clock partition that controls the RTC state. It is also required to maintain this value synchronized and valid at all times until the TPO value expires by recalculating the existing TPO value on the WDT. This is desired because the RTC may change before the WDT TPO value expires compromising the expected result.