International Business Machines Corporation

Ian A Concilio

Richard Gerard Hofmann

Chester A Heath

Nader Amini

Bechara F Boury

Terence J Lohman

Sherwood Brannon

Long D Ngyuen

Jorge F Lenta

Jeffrey A Hawthorne

A DMA controller is provided for transferring data between source and destination devices over an I/O bus. The DMA control circuit includes a bus interface unit for providing a bus size information at the beginning of each consecutive bus cycle and a look ahead responsive to the bus size information for providing a bus size control signal. A DMA control circuit responsive to the bus size control signal controls the bus width during contiguous transfer cycles. By dynamically adjusting the DMA control circuit, back to back data reads and writes may occur with no wait states inserted for generating the terminal count information.

Dynamic bus sizing of DMA transfers

In a computer system having both peripherals having their own DMA channel arbiter and peripherals having no arbiter, a separate arbitration unit, controlled directly by the CPU, is provided to arbitrate on behalf of peripherals having no arbiter. The CPU can thus freely assign different arbitration levels to such peripherals, and can instruct the arbitration unit to simultaneously arbitrate on different arbitration levels or for two or more DMA channels.

DMA access arbitration device in which CPU can arbitrate on behalf of

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Ian A Concilio