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US008533709B2 (12) United States Patent (10) Patent No.: US 8,533,709 B2 Nicholas et al. (45) Date of Patent: Sep. 10, 2013 (54) VIRTUALCHANGINGPROGRAMMABLE MACHINES FREQUENCY INTERRUPT T0 CONTROL OFAVIRTUAL TIMER IN 200336614073232006/0090092 A1 * 4/2006 Verhulstgakdiinentetlai‘if n e ......................a ' "" ~~~~~~~~~~~~ " ~~.. 713/400 VIRTUAL TIME OTHER PUBLICATIONS . Mock et a1. “Continuous clock s chroniZation in Wireless real-time (75) Inventors: Andrew Ernest Nicholas’ Beinevue’ WA applications”, Reliable Distributzid1 Systems, 2000, p. 125-132).* (Us); Rene Anton“) Vega’ Klrkland’ WA Cristian et a1. (“Clock Synchronization in the Presence of Omission (Us) and Performance Failures, and Processor Joins”, IBM Research, 16th IEEE Int. Symp. On Fault-tolerant Computing Systems, Vienna, Jul. (73) Assignee: Microsoft Cororation, Redmond, WA 19g6),* (US) Honeycutt, J., “Microsoft® Virtual PC”, Microsoft®, Nov. 2003, 1-27. ( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 * Cited by examiner U.S.C. 154(b) by 1649 days. Primary Examiner * Meng An (21) Appl. No.1 11/197,614 Assistant Examiner * Eric C Wai (74) Attorney, Agent, or Firm * Woodcock Washburn, LLP (22) Filed: Aug. 4, 2005 (57) ABSTRACT (65) Prior Publication Data . A catch-up mode that runs a v1rtua1 programmable rnterrupt US 2007/0033589 A1 Feb. 8, 2007 timer faster than a nominal rate to prevent time loss in a virtual machine can be implemented. If time loss is determined, a (51) Int- Cl- catch-up mode can be initiated to cause increased ?rings, G06F 9/45 5 (2006-01) beyond a nominal rate, of the programmable interrupt timer to (52) US Cl- adjust the clock of the virtual machine to the clock of the host USPC ...........................................................
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