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Synchronization and Recalculation of Timed Power On timestamps in an LPAR system with a virtualized clock

IP.com Disclosure Number: IPCOM000010321D
Original Publication Date: 2002-Nov-20
Included in the Prior Art Database: 2002-Nov-20
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Abstract

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.

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Synchronization and Recalculation of Timed Power On timestamps in an LPAR

system with a virtualized clock

On a system that supports Logical Partitioning (LPAR) and Timed Power On (TPO) functionality. If the system has a virtualized clock subsystem with the limitations of operating with only one physical battery-backed Real-Time Clock (RTC), and one Watchdog Timer (WDT). Because the implementation of virtual Time Of Day (TOD) subsystem allows each partition to maintain its own private time and assume that it is in full control of the RTC and WDT, a method to synchronize the RTC and the WDT is required for TPO to occur accurately.

The system makes utilization of the WDT timer to store a user defined TPO value, the TPO value is a TOD stamp representing a future state of when the system is to be powered on. Once the RTC reaches the WDT state the system is powered on. If a partition issuing a TPO command is in a different TOD state than the master clock's TOD, master clock partition (MP) has direct control over the RTC, might result on unwanted behavior. To accomplish the desired behavior a TOD value synchronized with the RTC is needed. Also it is important to maintain this value synchronized and valid at all times until the TPO value expires. If the RTC changes given that the TOD of the clock master partition changes, the TPO values for the non clock master partitions become invalid. To maintain the TPO value synchronized it is necessary to recalculate the WDT TPO value.

The goal of synchronizing the TPO date/time value with the RTC is accomplished by calculating a delta between the MP TOD and the TOD of the partition issuing the TPO. The delta then is added to the TPO timestamp value, note Diagram 1. To maintain the TPO values of the non master clock partitions valid, it is necessary to recalculate the values if the MP ch...