71 lines
2.5 KiB
ReStructuredText
71 lines
2.5 KiB
ReStructuredText
Dataflow synthesis
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##################
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Many hardware acceleration problems can be expressed in the dataflow paradigm. It models a program as a directed graph of the data flowing between functions. The nodes of the graph are functional units called actors, and the edges represent the connections (transporting data) between them.
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Actors communicate by exchanging data units called tokens. A token contains arbitrary (user-defined) data, which is a record containing one or many fields, a field being a bit vector or another record. Token exchanges are atomic (i.e. all fields are transferred at once from the transmitting actor to the receiving actor). The flow of tokens is controlled using handshake signals (strobe and acknowledgement).
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Actors
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******
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Overview
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========
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Actors in Migen are written directly in FHDL. This maximizes the flexibility: for example, an actor can implement a DMA master to read data from system memory.
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Common scheduling models
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========================
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Combinatorial
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-------------
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The actor datapath is made entirely of combinatorial logic. The handshake signals pass through. A small integer adder would use this model.
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N-sequential
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------------
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The actor consumes one token at its input, and it produces one output token after N cycles. It cannot accept new input tokens until it has produced its output. A multicycle integer divider would use this model.
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N-pipelined
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-----------
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This is similar to the sequential model, but the actor can always accept new input tokens. It produces an output token N cycles of latency after accepting an input token. A pipelined multiplier would use this model.
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The Migen actor library
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***********************
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Plumbing actors
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===============
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Structuring actors
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==================
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Simulation actors
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=================
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Arithmetic and logic actors
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===========================
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Bus actors
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==========
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Actor networks
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**************
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Actor networks are managed using the NetworkX [networkx]_ library.
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.. [networkx] http://networkx.lanl.gov/
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Performance tools
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*****************
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High-level actor description
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****************************
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.. WARNING::
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Not implemented yet, just an idea.
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It is conceivable that a CAL [cal]_ to FHDL compiler be implemented at some point, to support higher level descriptions of some actors and reuse of third-party RVC-CAL applications. [orcc]_ [orcapps]_ [opendf]_
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.. [cal] http://opendf.svn.sourceforge.net/viewvc/opendf/trunk/doc/GentleIntro/GentleIntro.pdf
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.. [orcc] http://orcc.sourceforge.net/
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.. [orcapps] http://orc-apps.sourceforge.net/
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.. [opendf] http://opendf.sourceforge.net/
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