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Browse Prior Art Database

Time-Of-Day Clock Comparator

IP.com Disclosure Number: IPCOM000047417D
Original Publication Date: 1983-Nov-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Curlee, TO: AUTHOR [+2]

Abstract

A comparison of maintenance and service support facility (MSSF) register time with time-of-day (TOD) time is implemented to include provision for the case where either operand had earlier been incremented to a resulting wrap-around value. The high-order 32 bits of the time-of-day clock, TOD (0:31), are periodically copied, incremented with a small value, W, and dispatched to a maintenance and service support facility register, MSSF (0:31). Incrementing is done wrap-around fashion; i.e., if the incremented value exceeds 32 bits, the overflow is ignored. The value W is guaranteed to contain two leading zeros when expressed as a 32-bit integer (0:31). The TOD clock is regularly advanced in wrap-around fashion.

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Time-Of-Day Clock Comparator

A comparison of maintenance and service support facility (MSSF) register time with time-of-day (TOD) time is implemented to include provision for the case where either operand had earlier been incremented to a resulting wrap-around value. The high-order 32 bits of the time-of-day clock, TOD (0:31), are periodically copied, incremented with a small value, W, and dispatched to a maintenance and service support facility register, MSSF (0:31). Incrementing is done wrap-around fashion; i.e., if the incremented value exceeds 32 bits, the overflow is ignored. The value W is guaranteed to contain two leading zeros when expressed as a 32-bit integer (0:31). The TOD clock is regularly advanced in wrap-around fashion. This is an architectural requirement, although wrap- around is not expected to occur during the practical life of the machine. Between successive periods of dispatching TOD (0:31) plus W to MSSF (0:31), the latter is frequently compared to the TOD (0:31) to determine if MSSF (0:31) > TOD (0:31) where either MSSF (0:31) or TOD (0:31) may represent wrap-around values.

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Without wrap-around, the comparison could be implemented according to the reference

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