Browse Prior Art Database

Bus Efficiency Improvement Via Timed PREEMPT

IP.com Disclosure Number: IPCOM000099975D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 1 page(s) / 54K

Publishing Venue

IBM

Related People

Keener, DS: AUTHOR [+2]

Abstract

This article describes a "PREEMPT to end of transfer (EOT)" hardware timer which is programmable to three time intervals of two, four or six microseconds.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 59% of the total text.

Bus Efficiency Improvement Via Timed PREEMPT

       This article describes a "PREEMPT to end of transfer
(EOT)" hardware timer which is programmable to three time intervals
of two, four or six microseconds.

      The MICRO CHANNEL* bus is a multi-master bus in a computer
system with mechanisms to share the bus with many attached devices.
The amount of continuous utilization that can be enjoyed by a single
adapter is limited by the PREEMPT mechanism and the inactive state.
If a bus master is the current bus owner and a PREEMPT signal is
activated, then the master must release the bus within 7.8
microseconds. This is to insure that memory refresh will continue
without interference.  Existing implementations of attachments
release the bus on the next transfer cycle.  This works, but when the
system becomes heavily loaded, the channel is reduced to an
arbitration, a single transfer, receipt of PREEMPT and bus release.
This series of events results in only one transfer per arbitration.
An arbitration cycle in a typical personal computer system requires
approximately 600 ns while a data transfer cycle requires 200 ns.
This results in 800 ns of time while only 200 ns of work is being
done.  It is very desirable that multiple transfers occur per
arbitration, since arbitrations are basically bus overhead and no
valid work occurs during this time.

      Recognizing that time is the critical factor for releasing the
bus after PREEMPT, a MICRO CHANNEL controller chip...