Expanding Direct Memory Access Capabilities to All Input/Output Devices
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
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.