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Concurrent Maintenance Functions for the Channel Adapters in a Communication Controller

IP.com Disclosure Number: IPCOM000034521D
Original Publication Date: 1989-Mar-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 6 page(s) / 51K

Publishing Venue

IBM

Related People

Austruy, P: AUTHOR [+4]

Abstract

In a communication controller such as shown in the drawing, several types of adapters are connected to a central control unit (CCU) through an input/output (I/O) bus to insure the exchange of information between devices connected to the line adapters (LAs) and host systems (not shown) through channel adapters (CAs). The channel adapters are interconnected in daisy chain configurations for selection purposes. This article describes how the channel adapters may be disconnected from the daisy chains while the communication controller continues to operate. The channel adapters are not only connected to the I/O bus but are also connected together in a daisy chain arrangement for two reasons: cycle steal and auto-selection.

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Concurrent Maintenance Functions for the Channel Adapters in a Communication Controller

In a communication controller such as shown in the drawing, several types of adapters are connected to a central control unit (CCU) through an input/output (I/O) bus to insure the exchange of information between devices connected to the line adapters (LAs) and host systems (not shown) through channel adapters (CAs). The channel adapters are interconnected in daisy chain configurations for selection purposes. This article describes how the channel adapters may be disconnected from the daisy chains while the communication controller continues to operate. The channel adapters are not only connected to the I/O bus but are also connected together in a daisy chain arrangement for two reasons: cycle steal and auto-selection. 1- Cycle steal daisy chain description: Each channel adapter transfers data from/to the central control unit through cycle steal operations. To initiate a cycle steal transfer, the channel adapter raises an I/O bus tag called "cycle steal request". This tag is common to all channel adapters attached to an I/O bus. When the central control unit accepts the cycle steal request, it raises another I/O tag, called "cycle steal grant" (CSG), on a line of the I/O bus. This tag is also common to all channel adapters. The CSG line enters the first channel adapter attached to the I/O bus and is propagated from one channel adapter to the next one on the I/O bus in order to reach any channel adapter which has issued the cycle steal request. The first channel adapter in the daisy chain which has requested the cycle steal traps the cycle steal grant signal and starts the data transfer with the central control unit. 2- Auto-selection daisy chain description: Interrupts at a given program level report to the central control unit requests for service. To report interrupts, the channel adapter raises a data bus line to the central control unit. This line is common to all channel adapters on an I/O bus, and any channel adapter can raise this line at any time. A channel adapter can report two types of interrupts to the central control unit: - high priority interrupt when the data transfer to the host has been initiated by the control program (CP) with high priority, and - low priority interrupt in all other cases. When an interrupt is detected by the control unit, control is given to the central control program run in the central control unit, which issues a command to all channel adapters on the bus to start the auto- selection. Auto-selection is a hardware mechanism which executes a circular poll of all channel adapters on the I/O bus to select the channel adapter which has the highest priority interrupt pending to become the adapter selected for service by the central control unit. The auto- selection starts from the previously last selected channel adapter. To implement this mechanism, all the channel adapters are also interconnected in the auto-...