Browse Prior Art Database

Overlapped Operations on Coupled Data Busses

IP.com Disclosure Number: IPCOM000112258D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Haess, J: AUTHOR [+3]

Abstract

In a system comprising a plurality of coupled busses, overlapped operations - especially of the outer busses - are advantageous in order to reduce the time a particular bus is busy for a single operation. Such a system is shown in the Figure, comprising an S-bus,V-bus, I-bus, a plurality of bus units BU, bus couplers BK1 and BK2, memory MEM, and processor PROC. A BU to MEM operation requires several system cycles on the S-bus, additional system cycles per bus coupler and for arbitration, totalling more than 20 cycles for which the I-bus is busy. Of those, 6 cycles can be recovered by overlapping the succeeding bus-operation.

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Overlapped Operations on Coupled Data Busses

      In a system comprising a plurality of coupled busses,
overlapped operations - especially of the outer busses - are
advantageous in order to reduce the time a particular bus is busy for
a single operation.  Such a system is shown in the Figure, comprising
an S-bus,V-bus, I-bus, a plurality of bus units BU, bus couplers BK1
and BK2, memory MEM, and processor PROC.  A BU to MEM operation
requires several system cycles on the S-bus, additional system cycles
per bus coupler and for arbitration, totalling more than 20 cycles
for which the I-bus is busy.  Of those, 6 cycles can be recovered by
overlapping the succeeding bus-operation.

      Operations on the S-bus may be classified according to their
maximum duration.  This allows BK1 to calculate the latest possible
operation end, based on command and address information.  Subtracting
the requested cycles of overlap, a signal 'coming end' is generated.
Getting the signal 'coming end', BK2 can already grant the next I-bus
operation, even the currently running operation is still using some
I-bus lines, thus implementing the operation-overlap.