Browse Prior Art Database

Docking Station Communication Link

IP.com Disclosure Number: IPCOM000111133D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 186K

Publishing Venue

IBM

Related People

Northard, RE: AUTHOR

Abstract

A method is provided for very efficient, reliable and rapid communications between inexpensive processors running at different speeds in a hostile environment, such as in a docking station in a vehicle, e.g., a truck.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 31% of the total text.

Docking Station Communication Link

      A method is provided for very efficient, reliable and rapid
communications between inexpensive processors running at different
speeds in a hostile environment, such as in a docking station in a
vehicle, e.g., a truck.

      A hand held tablet computer is used by a mobile work force
which must interface to various other processors in the vehicle.
This interface is accomplished by a permanently mounted holding
device located in the vehicle which is referred to as a docking
station, or holster.  The holster requirements may vary from user to
user, but it includes a mix of inexpensive processors which must
perform while the computerized tablet is removed from the holster.

      This method achieves the maximum transfer rate permitted by the
slower of two processors involved, which adjusts accordingly if this
rate varies, with assured error-free transmission.

      These objectives are met by using a standard half duplex
communication link to connect all processors.  Capitalizing on the
fact that a single byte of data can be communicated by serial
communications hardware, without intervention by the processor, this
method provides a signal that the processor has received the byte and
echoes the byte for verification that it arrived as sent.

      Synchronization between processors is accomplished by
alternating the direction of transmission between bytes.  For
example, during data transfer the sending unit transmits a byte and
then the receiving unit echoes the same byte back.  The echoed byte
facilitates comparison to ensure the correct byte was received and
signals that the receiving unit is ready for another byte.  It is the
duty of each processor to monitor activity while it is engaged in a
session on the serial link and to declare a timeout if activity
ceases.  If a timeout occurs the processor is set to the same status
as existed prior to the current session.  If the current session is
aborted while receiving, the received data is discarded, and if
aborted while transmitting, the entire message is held for later
transmission.  For example, if a comparison of the echoed byte
indicates that an error has occurred, the processor simply stops
sending and re-queues the message for transmission.  The processor
receiving the message will then timeout and discard whatever it has
received.  This provides both error free recovery and time for the
cause of the error, such as electrical noise, to have abated.  Since
the monitoring of activity on the serial bus requires a timer and
posting of a bit on serial interrupts, this approach provides a
method which is both low cost and easy to implement, yet provides a
degree of error handling with minimal amount of software.

      The docking station includes, e.g., eight processors attached
to sockets, with one processor, called the master processor, always
being present.  The master processor communicates to the hand held
tablet...