Continuous data transfer system

Abstract

Apparatus controls sequential direct memory access (DMA) transfers between a plurality of buffer memories and a data translation device. Each buffer memory has an overrun area associated with it. Prior to transfers from the buffer memories to the data translation device, the buffer memories are first 'threaded' together by loading the overrun area of a first buffer memory with data from the next buffer memory. During the DMA transfer, when the first buffer memory becomes empty a request is made to a computer to restart the DMA operation on the next sequential buffer, but while the request is being serviced, data is continually being transferred out of the first buffer's overrun area. Alternatively, for transfers from the data translation device to the buffer memories, after the first buffer memory is full, an interrupt is generated and incoming data is stored in the first buffer memory's overrun area while the interrupt is being serviced. After the interrupt is serviced, data is stored in the next sequential buffer memory in an area offset from the beginning thereof equal to the overrun area filled with data, the computer determining the exact point where the DMA process stopped depositing data in the overrun area by sequentially examining the entries in the overrun area. The computer then moves the data in the overrun area into the next buffer to complete the transfer.