40 lines
1.6 KiB
ReStructuredText
40 lines
1.6 KiB
ReStructuredText
.. _dma-devices:
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Adding a DMA Device
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===================
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DMA devices are Tilelink widgets which act as masters. In other words,
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DMA devices can send their own read and write requests to the chip's memory
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system.
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For IO devices or accelerators (like a disk or network driver), instead of
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having the CPU poll data from the device, we may want to have the device write
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directly to the coherent memory system instead. For example, here is a device
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that writes zeros to the memory at a configured address.
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.. literalinclude:: ../../generators/chipyard/src/main/scala/example/InitZero.scala
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:language: scala
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.. literalinclude:: ../../generators/chipyard/src/main/scala/DigitalTop.scala
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:language: scala
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:start-after: DOC include start: DigitalTop
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:end-before: DOC include end: DigitalTop
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We use ``TLHelper.makeClientNode`` to create a TileLink client node for us.
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We then connect the client node to the memory system through the front bus (fbus).
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For more info on creating TileLink client nodes, take a look at :ref:`TileLink-Diplomacy-Reference/NodeTypes:Client Node`.
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Once we've created our top-level module including the DMA widget, we can create a configuration for it as we did before.
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.. literalinclude:: ../../generators/chipyard/src/main/scala/example/InitZero.scala
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:language: scala
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:start-after: DOC include start: WithInitZero
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:end-before: DOC include end: WithInitZero
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.. literalinclude:: ../../generators/chipyard/src/main/scala/config/RocketConfigs.scala
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:language: scala
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:start-after: DOC include start: InitZeroRocketConfig
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:end-before: DOC include end: InitZeroRocketConfig
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