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32 lines
1.3 KiB
ReStructuredText
32 lines
1.3 KiB
ReStructuredText
Control and data flow
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=====================
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.. todo:: less academic
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The data- and control-flow of a typical synthesis tool is very similar to the
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data- and control-flow of a typical compiler: different subsystems are called in
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a predetermined order, each consuming the data generated by the last subsystem
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and generating the data for the next subsystem (see :numref:`Fig. %s
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<fig:approach_flow>`).
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.. figure:: /_images/approach_flow.*
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:class: width-helper
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:name: fig:approach_flow
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General data- and control-flow of a synthesis tool
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The first subsystem to be called is usually called a frontend. It does not
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process the data generated by another subsystem but instead reads the user
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input—in the case of a HDL synthesis tool, the behavioural HDL code.
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The subsystems that consume data from previous subsystems and produce data for
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the next subsystems (usually in the same or a similar format) are called passes.
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The last subsystem that is executed transforms the data generated by the last
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pass into a suitable output format and writes it to a disk file. This subsystem
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is usually called the backend.
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In Yosys all frontends, passes and backends are directly available as commands
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in the synthesis script. Thus the user can easily create a custom synthesis flow
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just by calling passes in the right order in a synthesis script.
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