Browse Prior Art Database

Input Output Channel Mechanism for Handling Control Unit Busy Status

IP.com Disclosure Number: IPCOM000087066D
Original Publication Date: 1976-Dec-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 45K

Publishing Venue

IBM

Related People

Boggs, JK: AUTHOR [+4]

Abstract

An input/output (I/O) channel mechanism is described which eliminates I/O interrupts caused by the occurrence of Control Unit Busy status and Control Unit End status. This mechanism enables the I/O channel to handle Control Unit Busy situations without reporting their occurrence to the operating system software. This reduces the I/O supervisor software overhead. The enqueuing of I/O requests is asynchronous. The I/O interface is not checked for busy conditions.

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Input Output Channel Mechanism for Handling Control Unit Busy Status

An input/output (I/O) channel mechanism is described which eliminates I/O interrupts caused by the occurrence of Control Unit Busy status and Control Unit End status. This mechanism enables the I/O channel to handle Control Unit Busy situations without reporting their occurrence to the operating system software. This reduces the I/O supervisor software overhead. The enqueuing of I/O requests is asynchronous. The I/O interface is not checked for busy conditions.

Fig. 1 shows the general environment and Fig. 2 shows the control block (CB) organization used to implement the improved channel mechanism in this Fig. 1 environment. The main storage shown in Fig. 1 includes a private or dedicated storage area which is set aside for exclusive use by the microcode which controls I/O operations. A control block is a parcel or chunk of storage space located in this private storage area.

As indicated in Fig. 2, each I/O control unit and each I/O device has its own separate control block. Each control block is used for storing various status information and control information for its corresponding control unit or I/O device. In particular, each control unit control block includes a control unit busy status bit which is turned on when the corresponding control unit is busy.

As part of this channel mechanism, each control unit control block also includes a control unit busy queue. Each such queue is a list of device control block (SB) addresses for those devices for which a processor originated I/O request has been received, while the control unit busy status bit in its control unit control block is on.

In effect, it is a list of those I/O devices which have processor-originated I/O requests which are being held up by the Control Unit Busy status.

Furthenmore, each device control block includes a field which contains the address of the control block for the control unit to which the device is connected....