Browse Prior Art Database

Limited Tolerance to Poll Response Delays

IP.com Disclosure Number: IPCOM000108021D
Original Publication Date: 1992-Jan-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 84K

Publishing Venue

IBM

Related People

Dancker, GA: AUTHOR [+3]

Abstract

A Work Station Controller (WSC) provides attachment of multiple work stations to a computer system via some type of communication protocol. WSCs typically poll attached work stations and wait for a poll response. A no response (time out) communication protocol error is retried some number of times. If a retry is successful, a temporary time out error is logged. This article describes how a WSC can adjust allowable poll response times (for individual work stations) and control the number of temporary time out errors, to fit the particular environment. (Image Omitted)

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Limited Tolerance to Poll Response Delays

       A Work Station Controller (WSC) provides attachment of
multiple work stations to a computer system via some type of
communication protocol.  WSCs typically poll attached work stations
and wait for a poll response.  A no response (time out) communication
protocol error is retried some number of times.  If a retry is
successful, a temporary time out error is logged.  This article
describes how a WSC can adjust allowable poll response times (for
individual work stations) and control the number of temporary time
out errors, to fit the particular environment.

                            (Image Omitted)

      Work stations can include dependent displays, programmable work
stations, printers, or other devices.  In some protocols, work
stations are allowed to cable-through, where multiple work stations
can attach to the same communication cable.  A typical local WSC with
attached work stations is shown in the figure.  This article also
applies to remote WSCs which attach to the host processor via a
communication line instead of system bus.

      WSCs poll attached work stations, checking for new status (for
example, a keystroke) or checking for completion of a previously sent
command.  The work station communication protocol defines valid poll
response timings. For example, when a work station receives a poll,
the work station should respond within 30 to 60 usec.

      The WSC microcode may be able to set the maximum poll response
delay time allowed by the WSC hardware.  When WSC hardware detects a
no-response to a poll causing an error, the WSC microcode will
typically be interrupted.  The WSC microcode will retry the poll some
number of times (for example, 16) and after 16 consecutive
no-response errors the work station is considered powered down (no
error is logged because this is the normal work station power-down
situation).  If a retry is successful, a temporary time out error is
be logged.

      A counter of the number of temporary time out errors which have
been detected and logged is maintained for each work station.  When
the counter reaches a threshold, the maximum allowable poll response
delay time is increased slightly.  Periodically, the counter is reset
and the allow...