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Resetting the Micro Channel Architecture Arbitration Time Dynamically using Lookahead

IP.com Disclosure Number: IPCOM000112243D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 87K

Publishing Venue

IBM

Related People

Durham, CL: AUTHOR [+5]

Abstract

As Micro Channel* Architecture systems grow in complexity and size, the length of time required for arbitration increases and varies (based on the number of participants, driver and backplane characteristics, and the arbitration levels contending for bus ownership). If the arbitration time is set too long, performance suffers. If the arbitration time is set too short, bus disruption and driver contention are more likely. In order to dynamically optimize the arbitration time, an invention is described whereby the centralized arbiter verifies a stable winner by use of a look-ahead feature.

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This is the abbreviated version, containing approximately 52% of the total text.

Resetting the Micro Channel Architecture Arbitration Time Dynamically
using Lookahead

      As Micro Channel* Architecture systems grow in complexity and
size, the length of time required for arbitration increases and
varies (based on the number of participants, driver and backplane
characteristics, and the arbitration levels contending for bus
ownership).  If the arbitration time is set too long, performance
suffers.  If the arbitration time is set too short, bus disruption
and driver contention are more likely.  In order to dynamically
optimize the arbitration time, an invention is described whereby the
centralized arbiter verifies a stable winner by use of a look-ahead
feature.

      In order to prevent driver contention, described is a method
whereby the Central Arbitration Control Point, or CACP, would
implement a look-ahead feature, validating the stability of the
arbitration bus prior to GRANT.  In its simplest form, a single
capture of the arbitration level prior to GRANT would be compared to
the resultant value at GRANT time.  If the two values were different,
the CACP would drive an asynchronous channel check until the Micro
Channel bus was released.  At that time, the CACP could internally
adjust the arbitration window and optionally report the new
arbitration time to the System Master.

      In a more complex form, the look-ahead function could repeat
until the two test values were identical.   The CACP in this case
could hold GRANT high until a winner could be established.  A timeout
counter may be necessary for severe cases when the bus never
stabilizes.  Then the system could revert to GRANTing the bus
followed by an asynchronous channel check, which could also be
designed to cause a system reset.

      This invention works particularly well with multiple
arbitration buses separated by an eXtended ARBitration controller
(Figure).  In this system, the XARB controller would implement the
look-ahead function by sampling the arbitration levels...