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Checking Scheme for Compares in a Queuing System

IP.com Disclosure Number: IPCOM000086099D
Original Publication Date: 1976-Jul-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 52K

Publishing Venue

IBM

Related People

Jones, JD: AUTHOR [+2]

Abstract

Many systems employ hardware queues which are dynamic shift registers that are dynamically compared at various positions with one or more other registers. This eliminates the necessity to duplicate all compares used in the dynamic queuing system in order to check the functionality of the compares.

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Checking Scheme for Compares in a Queuing System

Many systems employ hardware queues which are dynamic shift registers that are dynamically compared at various positions with one or more other registers. This eliminates the necessity to duplicate all compares used in the dynamic queuing system in order to check the functionality of the compares.

The buffer update address register (BUAR) holds the broadcasted address of a backing storage store operation done by another CPU. The broadcasted address is compared, at various positions, with the address of various pending stores. The address of any pending store will be in storage address register STAR 1 and/or STAR 2. If any of the compares malfunction, then a data integrity problem may exist between the `cache' and backing storage. Sophisticated diagnostics are being written to detect any malfunctions that may exist in the compares but when a nondiagnostic program is running, a dynamic check of the operability of the compares is needed.

When the broadcasted address is shifted thru the queue, the address (es) that it is being compared with may remain in STAR 1 and/or STAR 2 for some minimum time. When either storage address register (STAR) is loaded, a valid bit for that register is turned on. When the valid bit is reset, that particular storage address register will not be loaded with a new address for a minimum of two machine cycles. If use is made of the above facts, the following may be ascertained: 1. If STAR 1 and/or STAR 2 are valid and a valid address (address
X) enters the BUAR (at position one), the address in STAR 1 and/or STAR 2 will not change until after the address (address X) is shifted out of the BUAR. Therefore, if the BUAR at position one compares with STAR 1 and/or STAR 2, it should compare with STAR 1 and/or STAR 2 at position 3. 2. If STAR 1 and/or STAR 2 is valid when a valid BU address shifts into position 2, the address in STAR 1 and STAR 2 will not change until after the BU address is shifted out of the BUAR. Therefore, if the BUAR at position 2 compares with STAR 1 and/or STAR 2, it should compare with STAR 1 and/or STAR 2 at position 3. If any of the above is not true, i.e., if a valid BU request compares with a valid pending store address at one position but not at another, then the compare circuitry is malfunctioning. If one extends the aforementioned idea he may check the compare circuitry without requiring all 21 address bits to be the same. If 7 groups of 3 compares per group are implemented (1 group = 1 exclusive OR entity = 3 compares) advantage can be taken of the 7 subcompares. By generating even or odd parity for...