71 lines
2.1 KiB
ReStructuredText
71 lines
2.1 KiB
ReStructuredText
|
Dataflow synthesis
|
||
|
|
##################
|
||
|
|
|
||
|
|
Many hardware acceleration problems can be expressed in the dataflow paradigm, that is, using a directed graph representing the flow of data between actors.
|
||
|
|
|
||
|
|
Actors communicate by exchanging tokens, whose flow is controlled using handshake signals (strobe and acknowledgement).
|
||
|
|
|
||
|
|
Actors
|
||
|
|
******
|
||
|
|
|
||
|
|
Overview
|
||
|
|
========
|
||
|
|
|
||
|
|
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.
|
||
|
|
|
||
|
|
Common scheduling models
|
||
|
|
========================
|
||
|
|
|
||
|
|
Combinatorial
|
||
|
|
-------------
|
||
|
|
The actor datapath is made entirely of combinatorial logic. The handshake signals pass through. A small integer adder would use this model.
|
||
|
|
|
||
|
|
N-sequential
|
||
|
|
------------
|
||
|
|
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.
|
||
|
|
|
||
|
|
N-pipelined
|
||
|
|
-----------
|
||
|
|
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.
|
||
|
|
|
||
|
|
The Migen actor library
|
||
|
|
***********************
|
||
|
|
|
||
|
|
Plumbing actors
|
||
|
|
===============
|
||
|
|
|
||
|
|
Structuring actors
|
||
|
|
==================
|
||
|
|
|
||
|
|
Simulation actors
|
||
|
|
=================
|
||
|
|
|
||
|
|
Arithmetic and logic actors
|
||
|
|
===========================
|
||
|
|
|
||
|
|
Bus actors
|
||
|
|
==========
|
||
|
|
|
||
|
|
Actor networks
|
||
|
|
**************
|
||
|
|
|
||
|
|
Actor networks are managed using the NetworkX [networkx]_ library.
|
||
|
|
|
||
|
|
.. [networkx] http://networkx.lanl.gov/
|
||
|
|
|
||
|
|
Performance tools
|
||
|
|
*****************
|
||
|
|
|
||
|
|
|
||
|
|
High-level actor description
|
||
|
|
****************************
|
||
|
|
.. WARNING::
|
||
|
|
Not implemented yet, just an idea.
|
||
|
|
|
||
|
|
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]_
|
||
|
|
|
||
|
|
.. [cal] http://opendf.svn.sourceforge.net/viewvc/opendf/trunk/doc/GentleIntro/GentleIntro.pdf
|
||
|
|
.. [orcc] http://orcc.sourceforge.net/
|
||
|
|
.. [orcapps] http://orc-apps.sourceforge.net/
|
||
|
|
.. [opendf] http://opendf.sourceforge.net/
|