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Expanding Direct Memory Access Capabilities to All Input/Output Devices

IP.com Disclosure Number: IPCOM000043372D
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Doster, WA: AUTHOR [+3]

Abstract

A technique is described whereby Direct-Memory Access (DMA) capabilities in data processing systems may be expanded to include any Input/ Output (I/O) device which normally relies on Central Processing Unit (CPU) action to initiate and direct the I/O operations. In order to provide DMA capabilities to I/O attachments, a flag would be provided to indicate the state of the system memory. The flag indication would reside in either a dedicated memory location or in hardware in the DMA controller. The I/O attachment controls are adapted to test and selectively modify the indication, as required. When so adapted, an attachment controller finding the DMA flag in a not-busy condition could set it to a busy condition and initiate its own access. This may be done without processor intervention.

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Expanding Direct Memory Access Capabilities to All Input/Output Devices

A technique is described whereby Direct-Memory Access (DMA) capabilities in data processing systems may be expanded to include any Input/ Output (I/O) device which normally relies on Central Processing Unit (CPU) action to initiate and direct the I/O operations. In order to provide DMA capabilities to I/O attachments, a flag would be provided to indicate the state of the system memory. The flag indication would reside in either a dedicated memory location or in hardware in the DMA controller. The I/O attachment controls are adapted to test and selectively modify the indication, as required. When so adapted, an attachment controller finding the DMA flag in a not-busy condition could set it to a busy condition and initiate its own access. This may be done without processor intervention. If, however, the flag is found in a busy condition, the controller would exercise one of the following access options: 1. Retest the flag after a predetermined timeout, and

then use DMA access, if available. 2. Invoke conventional I/O, e.g., interrupt CPU for conventional I/O initiation. 3. Mix the first two options. Start the conventional I/O initiation but continue to test the flag status;

then use whichever method first becomes available. The use of this feature maximizes data throughput to any I/O device attachment capable of using DMA or programmed I/O, particularly in applications requiring shared direct-m...