Direct memory access unit for transferring data between processor

Abstract

There is provided a Direct Access Memory Unit (DAu) that is associated with a remote processor module in a multi-processing system. The DAU performs Direct Memory Access (DMA) operations independently of a Central Processing Unit (CPU) in the remote processor module. The CPU requests a DMA by writing information relevant to the DMA to the remote processor's memory. The address of each control block is written to a circular queue, also in the remote processor's memory. The DAU determines if there are any control blocks to process and if so, the DAU will perform the DMA operation (reading data from or writing data to the memory of the host processor), all without the intervention of the CPU of the remote processor module. The CPU adds a new control block by loading its address in a location in the circular queue that is ahead of the circular queue location that the DAU is processing. The CPU can abort a pending DMA request during DAU operations by setting a skip bit in the control block. Upon the completion of performing a DMA request, the DAU will set a complete bit in the control block in the remote processor's memory. An interrupt can also be sent to the CPU, wherein the CPU is advised that a DMA request has been completed. The data in a DMA operation is sent in bursts to a buffer located between two busses having different data transmission rates.