即时加速非对齐数据传输的dma设计方法

针对软件处理字节非对齐数据传输时效率低的问题，提出了一种资源占用少、低功耗的即时拼接直接存储器存取(DMA)设计方案。用户按照字节传输方式配置DMA进行非对齐数据传输，DMA控制器自动进行适当的字节拼合，从而以字传输方式完成数据传输。该方案不仅能够应对32位系统所有字节不对齐和递增递减方向的组合，而且完全由硬件电路处理、软件编程没有额外的开销，仿真验证表明，该设计方法能够显著加快32位低功耗SOC系统字节非对齐数据的传输速度。目前已经应用于一种用电采集MCU芯片，用于协助软件高速处理加解密数据、通信协议帧等，结果表明，该芯片的DMA模块传输速率高、操作简便，可以满足设计要求。

Method and implementation for DMA on the fly expediting transfer of unaligned data

We propose the design of DMA controller for 32 bits low power SOC system, which expedites transfer of unaligned data through on the fly reassembling bytes by hardware circuit, requiring fewer resources, power and no extra software overhead. Although user configures the transfer of unaligned data in byte format, the DMA controller can automatically reorganize bytes in proper way, so as to transfer data in word format correctly and faster. Verification shows the design can evidently improve transfer efficiency of unaligned data. The design method has been applied to a MCU chip for electricity information acquisition system, and assists software to deal with encryption and decryption, to form communication frames, etc. The results show that the DMA controller works with high efficiency while easy to use, so the design meets the requirements.