Direct memory access apparatus and methods for transferring data between

Abstract

Methods and apparatus are disclosed for transferring data to and from a first bus, to which a first set of high performance devices, including at least one central processing unit ('CPU') is attached, and a second bus, to which a second set of relatively lower performance devices is attached. More particularly the invention accomplishes the transfer function in a manner that facilitates communication between the first and second set of devices from the comparatively lower performance of the second set of devices. Direct memory access ('DMA') apparatus and methods are disclosed, including a set of direct memory access channels. The DMA channels may be used to transfer data between the high performance channel (hereinafter referred to as the 'Local Bus') coupled to the CPU in a reduced instruction set computer (RISC) system and a typically lower performance, peripheral bus (hereinafter referred to as a 'Remote Bus'). The resulting DMA interface between the Local Bus and a Remote Bus permits a wide performance range of standard peripheral devices to be attached to the RISC system in a manner that does not limit system performance. The noval DMA may also be used as part of a data transfer controller (DTC) having other components, such as I/O ports, or may be used independently for transferring data between unmatched buses in, for example, computer systems, data transmission systems and the like.