Browse Prior Art Database

Hardware Notification of a Disconnected SCSI Device

IP.com Disclosure Number: IPCOM000035255D
Original Publication Date: 1989-Jun-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Movall, PE: AUTHOR [+2]

Abstract

A hardware method is provided by which an adapter card can notify host system device driver code when a device disconnects from a Small Computer System Interface (SCSI) bus and the bus becomes free to be used for other devices.

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Hardware Notification of a Disconnected SCSI Device

A hardware method is provided by which an adapter card can notify host system device driver code when a device disconnects from a Small Computer System Interface (SCSI) bus and the bus becomes free to be used for other devices.

The SCSI standard is a local I/O bus developed to provide host systems with a device independent within a class of devices. The SCSI standard, ANSI X3.131-1986, provides mechanical, electrical, and functional specifications. It contains provisions for the connection of multiple initiators (SCSI devices capable of initiating an operation) and multiple targets (SCSI devices capable of responding to a request to perform an operation).

In a typical system with a local SCSI I/O bus (see Fig. 1), the host (initiator) will issue commands to the various SCSI devices (targets) via the SCSI adapter card. The SCSI devices may include optical disk drives, tapes drives, and hard disk drives. These commands may include reads, writes, seeks, and various status and selection commands.

Within the SCSI standard, there is a provision to allow a target device to disconnect from the bus during a long operation in which it does not use the bus. As an example, the tape drive can be commanded to perform a retention operation to the tape. This operation takes several minutes to complete, during which the bus is not required. The drive may therefore disconnect from the bus and thereby freeing the bus.

During this time, the bus is free to be used by another device. This disconnect status can and should be passed from adapter to the host system.

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This method requires both hardware and software. The key pieces of this hardware notification mechanism include: 1. Hardware interrupt from the adapter card to the device driver. 2. Hardware registers accessible to both the adapter card and the device driver. 3. Code which can recognize the disconnected status.

Item 1 is provided by both the adapter card, to generate th...