Real time clock (RTC) having several highly desira

专利名称：Real time clock (RTC) having several highly

desirable timekeeping dependability andsecurity attributes, and methods foraccessing a register thereof

发明人：James J. Walsh申请号：US09613008申请日：20000710公开号：US06772361B1公开日：20040803

专利附图：

摘要：A real time clock (RTC) is described several timekeeping dependability and

timekeeping security attributes. The RTC may have several registers for storing values, atleast one of which stores a value which is safeguarded. For example, a

“TrustQualityState” register stores a “TrustQualityState” value which is dependentupon a timekeeping accuracy of the RTC. The “TrustQualityState” value may also bedependent upon timekeeping stability, reliability, and/or security of the RTC (e.g., atamper resistance of the RTC). The RTC includes an access unit coupled between the“TrustQualityState” register and a bus used to access the “TrustQualityState”register. The access unit controls access to the “TrustQualityState” register in order tosafeguard the “TrustQualityState” value. The access unit receives read and writecommands directed to “TrustQualityState” register via the bus. The access unitdetermines if a source of a received read or write command directed to the register isauthorized to access the register, and provides access to the register only if the source isauthorized to access the register. The “TrustQualityState” value may expire a

predetermined period of time after issue. In this case, the access unit may also include acounter configured to issue a signal after the predetermined period of time. When theaccess unit receives the signal from the counter, the access unit may store a default valueof “0” in the “TrustQualityState” register.

申请人：ADVANCED MICRO DEVICES, INC.

代理机构：Meyertons Hood Kivlin Kowert & Goetzel, P.C.

代理人：B. Noël Kivlin

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