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<div class=" wh_topic_content body "><main role="main"><article class="- topic/topic concept/concept topic concept" role="article" aria-labelledby="ariaid-title1"><span class="edit-link" style="font-size:12px; opacity:0.6; text-align:right; vertical-align:middle"><a target="_blank" href="http://172.16.35.88/tasks/jdssno1uvvbf2mltu9kb9v3if05d5gopuakboe8hlud18rma/edit/F:/aicdita/aicdita-cn/topics/sdk/dma/dma-user-guide.dita">Edit online</a></span><h1 class="- topic/title title topictitle1" id="ariaid-title1">DMA 使用指南</h1><div class="date inPage">25 Nov 2024</div><div style="color: gray;">
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Read time: 1 minute(s)
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</div><div class="- topic/body concept/conbody body conbody"><div class="- topic/p p" data-ofbid="d353582e22__20250121172131">Direction memory access (DMA) 模块提供一种高效的数据传输技术，能够在不受 CPU 干预的情况下进行设备间的数据传输，从而减少 CPU 负荷。CPU
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使能 DMA 之后，就退出操作，由 DMA 独立自主控制数据传输。此外，DMA 提供的数据交换具有高带宽和低延迟的优点。<div class="- topic/note note note note_note" id="concept_or5_kn3_pzb__note_j3d_ywx_bdc" data-ofbid="concept_or5_kn3_pzb__note_j3d_ywx_bdc"><span class="note__title">注：</span> 关于 DMA 可以连接的设备列表，可查看具体产品型号对应的数据手册。关于 DMA 存储单元的详细说明，可查看具体产品型号用户手册的功能框图。</div></div><div class="- topic/note note note note_note" id="concept_or5_kn3_pzb__note_ddj_kwj_bdc" data-ofbid="concept_or5_kn3_pzb__note_ddj_kwj_bdc"><span class="note__title">注：</span> USB、GMAC、eMMC 等模块具有内置的 DMA。为了方便区分，本模块可视作通用 DMA 模块，不适用于具有内置 DMA
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的硬件模块。</div><div class="table-container"><table class="- topic/table table frame-all" id="concept_or5_kn3_pzb__table_bdk_xwd_hzb" data-ofbid="concept_or5_kn3_pzb__table_bdk_xwd_hzb" data-cols="3"><caption class="- topic/title title tablecap" data-caption-side="top" data-is-repeated="true"><span class="table--title-label">表<span class="table--title-label-number"> 1</span><span class="table--title-label-punctuation">. </span></span><span class="table--title">术语定义</span></caption><colgroup><col style="width:25%"/><col style="width:37.5%"/><col style="width:37.5%"/></colgroup><thead class="- topic/thead thead"><tr class="- topic/row"><th class="- topic/entry entry colsep-0 rowsep-0" id="concept_or5_kn3_pzb__table_bdk_xwd_hzb__entry__1">术语</th><th class="- topic/entry entry colsep-0 rowsep-0" id="concept_or5_kn3_pzb__table_bdk_xwd_hzb__entry__2">定义</th><th class="- topic/entry entry colsep-0 rowsep-0" id="concept_or5_kn3_pzb__table_bdk_xwd_hzb__entry__3">注释说明</th></tr></thead><tbody class="- topic/tbody tbody"><tr class="- topic/row"><td class="- topic/entry entry colsep-0 rowsep-0" headers="concept_or5_kn3_pzb__table_bdk_xwd_hzb__entry__1">DMA</td><td class="- topic/entry entry colsep-0 rowsep-0" headers="concept_or5_kn3_pzb__table_bdk_xwd_hzb__entry__2">Direct Memory Access</td><td class="- topic/entry entry colsep-0 rowsep-0" headers="concept_or5_kn3_pzb__table_bdk_xwd_hzb__entry__3">直接存储器访问</td></tr><tr class="- topic/row"><td class="- topic/entry entry colsep-0 rowsep-0" headers="concept_or5_kn3_pzb__table_bdk_xwd_hzb__entry__1">DRQ</td><td class="- topic/entry entry colsep-0 rowsep-0" headers="concept_or5_kn3_pzb__table_bdk_xwd_hzb__entry__2">DMA Request</td><td class="- topic/entry entry colsep-0 rowsep-0" headers="concept_or5_kn3_pzb__table_bdk_xwd_hzb__entry__3">指 DMA 请求的端口号</td></tr></tbody></table></div><div class="- topic/p p" data-ofbid="d353582e58__20250121172131">DMA 模块特性：<ul class="- topic/ul ul" id="concept_or5_kn3_pzb__ul_ddk_xwd_hzb" data-ofbid="concept_or5_kn3_pzb__ul_ddk_xwd_hzb"><li class="- topic/li li" data-ofbid="d353582e61__20250121172131">
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<p class="- topic/p p" data-ofbid="d353582e63__20250121172131">支持八个 DMA 通道，每通道有 32 个源端和 32 个终端可选</p>
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</li><li class="- topic/li li" data-ofbid="d353582e66__20250121172131">
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<p class="- topic/p p" data-ofbid="d353582e68__20250121172131">采用链表配置方式，寄存器描述通道状态</p>
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</li><li class="- topic/li li" data-ofbid="d353582e71__20250121172131">
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<p class="- topic/p p" data-ofbid="d353582e73__20250121172131">设备位宽支持 8/ 16/ 32/ 64 位，Burst 长度支持 1/ 4/ 8/ 16 个</p>
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</li><li class="- topic/li li" data-ofbid="d353582e76__20250121172131">
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<p class="- topic/p p" data-ofbid="d353582e78__20250121172131">DMA 源端、终端地址 8Byte 对齐</p>
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</li></ul></div><figure class="- topic/fig fig fignone" id="concept_or5_kn3_pzb__fig_qvh_1ks_c1c" data-ofbid="concept_or5_kn3_pzb__fig_qvh_1ks_c1c"><div class="- topic/p p" data-ofbid="d353582e84__20250121172131">
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<br/><div class="imagecenter"><img class="- topic/image image imagecenter" id="concept_or5_kn3_pzb__image_ucv_yjs_c1c" src="../../../images/dma/hw_system1.png" width="384" alt="dma_hw_system"/></div><br/>
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</div><figcaption data-caption-side="bottom" class="- topic/title title figcap"><span class="figtitleprefix fig--title-label">图<span class="fig--title-label-number"> 1</span><span class="fig--title-label-punctuation">. </span></span><span class="fig--title">DMA 硬件的原理框图</span></figcaption></figure><p class="- topic/p p" data-ofbid="d353582e91__20250121172131">根据数据的源和目的，DMA
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操作分为以下几种情况：</p><div class="table-container"><table class="- topic/table table frame-all" id="concept_or5_kn3_pzb__table_ncz_23d_bdc" data-ofbid="concept_or5_kn3_pzb__table_ncz_23d_bdc" data-cols="4"><caption class="- topic/title title tablecap" data-caption-side="top" data-is-repeated="true"><span class="table--title-label">表<span class="table--title-label-number"> 2</span><span class="table--title-label-punctuation">. </span></span><span class="table--title">DMA 操作定义</span></caption><colgroup><col style="width:4%"/><col style="width:16%"/><col style="width:40%"/><col style="width:40%"/></colgroup><thead class="- topic/thead thead"><tr class="- topic/row"><th class="- topic/entry entry colsep-1 rowsep-1" id="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__1">-</th><th class="- topic/entry entry colsep-1 rowsep-1" id="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__2">内核中类型定义</th><th class="- topic/entry entry colsep-1 rowsep-1" id="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__3">含义</th><th class="- topic/entry entry colsep-0 rowsep-1" id="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__4">特点</th></tr></thead><tbody class="- topic/tbody tbody"><tr class="- topic/row"><td class="- topic/entry entry colsep-1 rowsep-1" headers="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__1">1</td><td class="- topic/entry entry colsep-1 rowsep-1" headers="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__2">DMA_MEM_TO_MEM</td><td class="- topic/entry entry colsep-1 rowsep-1" headers="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__3"><p class="- topic/p p" data-ofbid="d353582e123__20250121172131">从内存到内存</p>将数据从一个内存区域复制到另一个内存区域（包括 DRAM、SRAM），可以看作是 memcpy()
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的硬件加速版本，用于高效地在内存中移动大量数据。</td><td class="- topic/entry entry colsep-0 rowsep-1" headers="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__4">由于只涉及内存操作，不涉及设备，因此操作相对简单，不需要握手信号或 FIFO。</td></tr><tr class="- topic/row"><td class="- topic/entry entry colsep-1 rowsep-1" headers="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__1">2</td><td class="- topic/entry entry colsep-1 rowsep-1" headers="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__2">DMA_MEM_TO_DEV</td><td class="- topic/entry entry colsep-1 rowsep-1" headers="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__3"><p class="- topic/p p" data-ofbid="d353582e134__20250121172131">从内存到设备</p>将数据从内存传输到设备，数据源是内存，而数据目的地是设备。这要求设备能够接收来自内存的数据，并可能需要一些控制逻辑来处理数据传输过程。</td><td class="- topic/entry entry colsep-0 rowsep-1" headers="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__4">支持 DMA 操作的设备一般需要提供握手信号或 FIFO 来确保数据传输的正确性和同步性。</td></tr><tr class="- topic/row"><td class="- topic/entry entry colsep-1 rowsep-1" headers="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__1">3</td><td class="- topic/entry entry colsep-1 rowsep-1" headers="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__2">DMA_DEV_TO_MEM</td><td class="- topic/entry entry colsep-1 rowsep-1" headers="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__3"><p class="- topic/p p" data-ofbid="d353582e145__20250121172131">从设备到内存</p>数据从设备传输到内存，是 DMA_MEM_TO_DEV
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的逆操作，允许设备将其数据处理结果或其他信息直接写入内存。</td><td class="- topic/entry entry colsep-0 rowsep-1" headers="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__4">需要设备提供相应的握手信号或 FIFO 以确保数据传输的稳定性和正确性。</td></tr><tr class="- topic/row"><td class="- topic/entry entry colsep-1 rowsep-0" headers="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__1">4</td><td class="- topic/entry entry colsep-1 rowsep-0" headers="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__2">DMA_DEV_TO_DEV</td><td class="- topic/entry entry colsep-1 rowsep-0" headers="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__3"><p class="- topic/p p" data-ofbid="d353582e156__20250121172131">从设备到设备</p>将数据直接从一个设备传输到另一个设备，而不经过 CPU 或内存。</td><td class="- topic/entry entry colsep-0 rowsep-0" headers="concept_or5_kn3_pzb__table_ncz_23d_bdc__entry__4">要求两个设备之间有直接的数据通路，使用场景较少。</td></tr></tbody></table></div></div></article></main></div>
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