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Dma-Driven Peripheral Device Controller Attachment in a Non-Dma System Environment

IP.com Disclosure Number: IPCOM000046769D
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 36K

Publishing Venue

IBM

Related People

Krishnamurty, R: AUTHOR [+3]

Abstract

Frequently in small microprocessor systems the need arises to attach a peripheral device controller, such as a CRT controller or a floppy diskette controller, that uses DMA (Direct Memory Access) to transfer data to and/or from the main system memory. In many cases the attachment of such a device poses problems because of one or more of the following reasons: 1. The system in question does not have a DMA controller to perform the necessary control functions. 2. The system microprocessor is not set up to operate in a DMA environment, i.e., the microprocessor does not have the required control signals, such as HOLD and HOLD ACKNOWLEDGE, that would allow an external device, such as a DMA controller, to take control of the data and address buses. 3.

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Dma-Driven Peripheral Device Controller Attachment in a Non-Dma System Environment

Frequently in small microprocessor systems the need arises to attach a peripheral device controller, such as a CRT controller or a floppy diskette controller, that uses DMA (Direct Memory Access) to transfer data to and/or from the main system memory. In many cases the attachment of such a device poses problems because of one or more of the following reasons: 1. The system in question does not have a DMA controller to perform the necessary control

functions. 2. The system microprocessor is not set up to operate

in a DMA environment, i.e., the microprocessor

does not have the required control signals, such

as HOLD and HOLD ACKNOWLEDGE, that would allow an

external device, such as a DMA controller, to take

control of the data and address buses. 3. The microprocessor utilization is high enough, and there are critical response time requirements

elsewhere in the system that preclude a DMA-driven

device from stealing processor cycles to perform

DMA transfers. 4. Some peripheral device controllers may be put in a

non-DMA mode wherein data transfers occur via PIO

(programmed input/ output); however, even without

the DMA requirement, many microprocessor systems

do not have the required speed to operate in this

mode. The figure illustrates a technique for attaching a DMA-driven peripheral device controller to a system that may have one or more of the limitations set forth above. As shown in the figure, the system processor sends commands to the peripheral controller over buses A and B. Once a command has been sent, bus B is isolated fro...