Apparatus and method for transferring multi-byte words in a fly-by dma operation

Abstract

An apparatus and method for transferring multi-byte words having arbitrary start and end byte addresses are described. Data transfers between a memory and a PCI-bus pass through a PCI-side aligner unit, PCI FIFO, Endian swap logic, and PCI-bus interface unit under the control of a PCI FIFO controller. The PCI-side aligner unit properly aligns the data while communicating data with the memory's bus on a word-at-a-time basis, and communicating data with the PCI FIFO managed on a byte-at-a-time basis synchronous with a clock signal provided by the memory's bus. The Endian swap logic properly orients the data in big or little Endian orientation. The PCI-bus interface unit communicates data with the PCI-bus on a word-at-a-time basis, and communicates data with the PCI FIFO managed on a byte-at-a-time basis synchronous with a clock signal provided by the PCI-bus. To keep track of unread stored data in the PCI FIFO, the PCI FIFO controller includes a #Bytes logic unit that automatically accounts for wrap-around of write and read pointers for the PCI FIFO.