Browse Prior Art Database

Bus Request Cancellation

IP.com Disclosure Number: IPCOM000120285D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 1 page(s) / 39K

Publishing Venue

IBM

Related People

Zenhari, GR: AUTHOR

Abstract

Disclosed is a method of cancelling a connect or disconnect request when a request from a remote Port Adapter (PA) is received.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 100% of the total text.

Bus Request Cancellation

      Disclosed is a method of cancelling a connect or disconnect
request when a request from a remote Port Adapter (PA) is received.

      There are 16 PA chips in the fiber optic switch.  They all
communicate with the switch processor over a common bus called CP
bus.  Each PA arbitrates for the bus by asserting its request on
specific bus cycles and removes it when granted.  Due to the
asynchronous nature of the fiber optic link, it is sometimes possible
that a port receives a connect/disconnect command from another port
or detects an arbitration error while waiting for a grant to its
request. In this case, this port should cancel its request and honor
the command received from the remote port.

      When this situation arises, the port receiving the remote
command resets its request, and all other control latches, and
prevents this port to be bus master, and honors the command received.
This is timing critical and it has to be done at the right cycle
without affecting the normal operation.

      As shown in the figure, although PA-0 has received a grant to
its request, it will not be a bus master in the next bus cycle since
it has received a PA-1 CMD and it is connected to PA-1.  Therefore,
PA-0 has to prevent issuing a command to PA-0.

      Disclosed anonymously.