Method and apparatus to reduce serial communications path connection overhead

Abstract

Control of a loop of a fiber-channel arbitrated-loop serial communications channel is maintained (i.e., the loop connection is held open) as long as a minimum amount of data, which optionally is determined by programming (called a “programmable amount of data”), is available for transmission, in order to reduce the overall amount of time spent arbitrating for control of the loop. The improved communications channel system includes a channel node having one or more ports, each port supporting a fiber-channel arbitrated-loop serial communications channel loop, wherein each port arbitrates for control of that port's attached channel loop. The system also includes an arbitration-and-control apparatus to reduce arbitrated-loop overhead, wherein control of the channel loop, once control is achieved by arbitration, is maintained by the arbitration-and-control apparatus as long as a predetermined amount of data is available within control of the node. In addition, a method to reduce arbitrated-loop overhead is described.Control of a serial communications path is maintained (i.e., the connection is held open) as long as a minimum amount of data, which optionally is determined by programming (called a “programmable amount of data”), is available for transmission, in order to reduce the overall amount of time spent opening the connection to the serial communications path. The system includes a serial device having n ports (where n equals one or more), each port supporting a serial communications path. Each port arbitrates for control of that port's attached serial communications path. The system also includes an arbitration-and-control apparatus, wherein control of the serial communications path, once control is achieved, is maintained by the arbitration-and-control apparatus as long as a predetermined amount of data is available within control of the serial device. In addition, a method to reduce connection overhead is described.<?insert-end id="INS-S-00001" ?>

Description

RELATED APPLICATIONS[0001]This application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application Ser. No. 60 / 065,920 filed Nov. 17, 1997, U.S. Provisional Application Ser. No. 60 / 065,926 filed Nov. 17, 1997, U.S. Provisional Application Ser. No. 60 / 065,919 filed Nov. 17, 1997, and U.S. Provisional Application Ser. No. 60 / 067,211 filed Dec. 1, 1997.[0002]This application is related to the following applications filed on even data herewith, each of which is incorporated by reference:“Method and Dedicated Frame Buffer for Loop Initialization and Responses” by Judy Lynn Westby, “Method and Dedicated Frame Buffers for Receiving Frames” by Judy Lynn Westby, and “Method and Apparatus for Using CRC for Data Integrity in On-Chip Memory” by Judy Lynn Westby.FIELD OF THE INVENTION[0003]The present invention relates to the field of mass-storage devices. More particularly, this invention relates to an improved fiber-channel arbitrated-loop (“FC-AL”) apparatus and method to re...

AI Technical Summary

Benefits of technology

"The present invention provides a method and apparatus to reduce arbitrated-loop overhead in a fiber-channel system. By maintaining control of the loop as long as a predetermined amount of data is available, the overall amount of time spent on arbitration is reduced. This is achieved by arbitrating for control of the loop and then maintaining control as long as a minimum amount of data is available within the control node. The system includes a channel-node circuit chip and an off-chip memory for storing data. The method can be implemented in a communications channel system with a first and second channel node, and a magnetic-disc-storage drive and computer system can be coupled through the fiber-channel arbitrated-loop serial-communications channel. The technical effect of the invention is to reduce the time and resources required for arbitration and control of the fiber-channel system."

Problems solved by technology

This meant that if one port was receiving or transmitting a frame, the alternate port was effectively busy (since it could not simultaneously use the frame-validation and frame-generation logic), and the alternate port was thus forced to deny its host-bus adapter permission to send frames.

Also, the drive was only able to transmit on one port at a time.

Hence, incoming data cannot be received on the other ports and the other ports are limited to the function of data transmission.

However, if a loop-interface module connected to the loop is already receiving data through a port connected to another loop, that loop-interface module might not be able to receive the loop-initialization data.

Moreover, if the loop-interface modules can receive only on one loop at a time, the modules cannot receive data through another port while loop initialization is occurring on one channel.

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