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专利名称：Method and apparatus for dynamic chaining
of DMA operations without incurring raceconditions
发明人：Martin Sodos申请号：US07/815802申请日：19911230公开号：US05367639A公开日：19941122
摘要：An apparatus and method for performing direct memory access (DMA) toinput/output (I/O) devices are described. In order to overcome storage limitations of aDMA controller, channel control blocks (CCBs) are stored in external memory. The DMAcontroller is programmed to reference a particular address of the external memorywhen a predetermined bit, referred to as a chain bit, in a current channel control block isset. The DMA controller will then perform a memory read operation on that area ofmemory and store a retrieved channel control block at a location previously utilized byan earlier channel control block. This process will continue until the chain bit is reset, atwhich time a DMA operation is complete. Dynamic chaining is easily accommodatedwhereby channel control blocks can be dynamically changed during the DMA access toprovide a flexible I/O system. The apparatus and method may be used to implementdynamic chaining without incurring race conditions. A wait bit is provided in each channelcontrol block and, when this bit is set, the DMA controller will suspend operationsthereby providing an opportunity for updating a chain of CCBs without incurring errorsdue to race conditions. Once the chain has been modified, the wait bit is reset and
processing safely continues.
申请人：SUN MICROSYSTEMS, INC.
代理机构：Blakely Sokoloff Taylor & Zafman
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