doc/dataflow.rst

   1 Dataflow synthesis
   2 ##################
   3
   4 Many hardware acceleration problems can be expressed in the dataflow paradigm, that is, using a directed graph representing the flow of data between actors.
   5
   6 Actors communicate by exchanging tokens, whose flow is controlled using handshake signals (strobe and acknowledgement).
   7
   8 Actors
   9 ******
  10
  11 Overview
  12 ========
  13
  14 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.
  15
  16 Common scheduling models
  17 ========================
  18
  19 Combinatorial
  20 -------------
  21 The actor datapath is made entirely of combinatorial logic. The handshake signals pass through. A small integer adder would use this model.
  22
  23 N-sequential
  24 ------------
  25 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.
  26
  27 N-pipelined
  28 -----------
  29 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.
  30
  31 The Migen actor library
  32 ***********************
  33
  34 Plumbing actors
  35 ===============
  36
  37 Structuring actors
  38 ==================
  39
  40 Simulation actors
  41 =================
  42
  43 Arithmetic and logic actors
  44 ===========================
  45
  46 Bus actors
  47 ==========
  48
  49 Actor networks
  50 **************
  51
  52 Actor networks are managed using the NetworkX [networkx]_ library.
  53
  54 .. [networkx] http://networkx.lanl.gov/
  55
  56 Performance tools
  57 *****************
  58
  59
  60 High-level actor description
  61 ****************************
  62 .. WARNING::
  63    Not implemented yet, just an idea.
  64
  65 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]_
  66
  67 .. [cal] http://opendf.svn.sourceforge.net/viewvc/opendf/trunk/doc/GentleIntro/GentleIntro.pdf
  68 .. [orcc] http://orcc.sourceforge.net/
  69 .. [orcapps] http://orc-apps.sourceforge.net/
  70 .. [opendf] http://opendf.sourceforge.net/