| 摘要 |
In conventional storage device system, data transfer from memory to IO bus has to go through an intermediate volatile memory (cache). Data transfer therefore is completed in two steps-data is transferred from memory to cache and then from cache to the IO bus. Memory-to-cache transfer is handled by one DMA engine and another DMA engine for cache-to-IO transfer. To start the transfer, processor prepares the DMA transfer from memory to cache. Upon completion of the memory-to-cache transfer, the processor is interrupted to prepare the transfer from cache to IO. In between transfers, the processor has to intervene to setup the next transfer utilizing the precious processor cycles. The present invention improves on the above process using two novel schemes; 1) The use of dependency table to facilitate the transfer from memory-to-IO with less intervention from the processor and 2) the use of Bus Snooping scheme to bypass the transfer to cache making the transfer directly from memory to IO bus. This makes the transfer from memory to IO completed in single transfer.
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