Reference-Page-For: Yosys is a framework for Verilog RTL synthesis

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About YoSys Open Synthesis Suite 

Yosys is a framework for Verilog RTL synthesis. It currently has extensive Verilog-2005 support and provides a basic set of synthesis algorithms for various application domains. Selected features and typical applications:

• Process almost any synthesizable Verilog-2005 design
• Converting Verilog to BLIF / EDIF/ BTOR / SMT-LIB / simple RTL Verilog / etc.
• Built-in formal methods for checking properties and equivalence
• Mapping to ASIC standard cell libraries (in Liberty File Format)
• Mapping to Xilinx 7-Series and Lattice iCE40 FPGAs
• Foundation and/or front-end for custom flows

Yosys can be adapted to perform any synthesis job by combining the existing passes (algorithms) using synthesis scripts and adding additional passes as needed by extending the Yosys C++ code base.
Yosys is free software licensed under the ISC license (a GPL compatible license that is similar in terms to the MIT license or the 2-clause BSD license).

Example Usage

Yosys is controlled using synthesis scripts. For example, the following Yosys synthesis script reads a design (with the top module mytop) from the verilog file mydesign.v, synthesizes it to a gate-level netlist using the cell library in the Liberty file mycells.lib and writes the synthesized results as Verilog netlist to synth.v:

# read design 
read_verilog mydesign.v

# elaborate design hierarchy
hierarchy -check -top mytop

# the high-level stuff
proc; opt; fsm; opt; memory; opt

# mapping to internal cell library
techmap; opt

# mapping flip-flops to mycells.lib
dfflibmap -liberty mycells.lib

# mapping logic to mycells.lib
abc -liberty mycells.lib

# cleanup
clean

# write synthesized design
write_verilog synth.v

The synth command provides a good default script that can be used as basis for simple synthesis scripts:

# read design 
read_verilog mydesign.v

# generic synthesis
synth -top mytop

# mapping to mycells.lib
dfflibmap -liberty mycells.lib
abc -liberty mycells.lib
clean

# write synthesized design
write_verilog synth.v

See help synth for details on the synth command.

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Links

First link below is the YoSysHQ GitHub Link:

YosysHQ/yosys 

All other links below-this-line are to other projects.

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Online Services

• EDA Playground -- Web Interface to many EDA tools, including Yosys
• Blinklight -- A visual FPGA dev tool for simple designs

Free Verilog Simulators

• Icarus Verilog
• Verilator

Free Software for High-Level Circuit Synthesis and/or Analysis

• Chisel -- Constructing Hardware in a Scala Embedded Language
• PandA -- high-level synthesis of C based descriptions
• CLaSH -- A compiler from Haskell to Verilog/VHDL
• MyHDL -- an open source Python package that lets you go from Python to silicon
• Migen -- a Python-based tool that aims at automating further the VLSI design process
• Cx -- A modern C-like language to create digital hardware

Free Software for Low-Level Circuit Synthesis and/or Analysis

• ABC -- extensive tools for synthesis and verification of binary sequential logic
• AIGER -- a format, library and set of utilities for And-Inverter Graphs
• MiniSAT -- the SAT solver library used in Yosys
• Torc -- infrastructure and tool set for mapping, placing, and routing
• RapidSmith -- a research-based, open source FPGA CAD tool for modern Xilinx FPGAs
• Open Circuit Design -- collection of open-source EDA tools, including Qflow
• Coriolis2 -- an ASIC place and route flow
• Workcraft -- a framework for interpreted graph models
• netlistsvg -- SVG schematic from a Yosys JSON netlist

Verilog Tutorials

• Learning Verilog with Yosys
• Numato Lab Verilog Tutorial
• ASIC-World Verilog Tutorial
• Nandland: Verilog Examples, Tutorials, and more 

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Documentation

This page has links to all the documentation resources available for Yosys.

Yosys Manual

A quick first-steps tutorial can be found in the README file.
The Yosys manual can be downloaded here (PDF).

Support

The best places to ask questions are the Yosys Subreddit, Stack Overflow and #yosys on freenode. The best place to report a bug is on GitHub.

Presentation Slides

This presentation slides cover a wide range of topics related to Yosys. (The LaTeX source is part of the Yosys source distribution. Fell free to adapt the slides as needed.)

Application Notes

• Yosys AppNote 010: Converting Verilog to BLIF
• Yosys AppNote 011: Interactive Design Investigation
• Yosys AppNote 012: Converting Verilog to BTOR

Papers and other Publications

This section is under construction.

• Clifford Wolf, Johann Glaser. Yosys - A Free Verilog Synthesis Suite. In Proceedings of Austrochip 2013. [download pdf]
• Johann Glaser and Clifford Wolf. Methodology and Example-Driven Interconnect Synthesis for Designing Heterogeneous Coarse-Grain Reconfigurable Architectures. In Jan Haase, editor, Models, Methods, and Tools for Complex Chip Design. Lecture Notes in Electrical Engineering. Volume 265, 2014, pp 201-221. Springer, 2013. [download pdf]

In papers and reports, please refer to Yosys as follows: Clifford Wolf. Yosys Open SYnthesis Suite. http://www.clifford.at/yosys/, e.g. using the following BibTeX code:

@MISC{Yosys,
 author = {Clifford Wolf},
 title = {Yosys Open SYnthesis Suite},
 howpublished = "\url{http://www.clifford.at/yosys/}"
}

Command Reference

• abc use ABC for technology mapping
• add add objects to the design
• aigmap map logic to and-inverter-graph circuit
• alumacc extract ALU and MACC cells
• assertpmux convert internal signals to module ports
• async2sync convert async FF inputs to sync circuits
• attrmap renaming attributes
• attrmvcp move or copy attributes from wires to driving cells
• blackbox change type of cells in the design
• cd a shortcut for 'select -module <name>'
• check check for obvious problems in the design
• chformal change formal constraints of the design
• chparam re-evaluate modules with new parameters
• chtype change type of cells in the design
• clean remove unused cells and wires
• clk2fflogic convert clocked FFs to generic $ff cells
• connect create or remove connections
• connwrappers match width of input-output port pairs
• coolrunner2_sop break $sop cells into ANDTERM/ORTERM cells
• copy copy modules in the design
• cover print code coverage counters
• delete delete objects in the design
• deminout demote inout ports to input or output
• design save, restore and reset current design
• dff2dffe transform $dff cells to $dffe cells
• dff2dffs process sync set/reset with SR over CE priority
• dffinit set INIT param on FF cells
• dfflibmap technology mapping of flip-flops
• dffsr2dff convert DFFSR cells to simpler FF cell types
• dump print parts of the design in ilang format
• echo turning echoing back of commands on and off
• edgetypes list all types of edges in selection
• equiv_add add a $equiv cell
• equiv_induct proving $equiv cells using temporal induction
• equiv_make prepare a circuit for equivalence checking
• equiv_mark mark equivalence checking regions
• equiv_miter extract miter from equiv circuit
• equiv_purge purge equivalence checking module
• equiv_remove remove $equiv cells
• equiv_simple try proving simple $equiv instances
• equiv_status print status of equivalent checking module
• equiv_struct structural equivalence checking
• eval evaluate the circuit given an input
• expose convert internal signals to module ports
• extract find subcircuits and replace them with cells
• extract_counter Extract GreenPak4 counter cells
• extract_fa find and extract full/half adders
• extract_reduce converts gate chains into $reduce_* cells
• flatten flatten design
• freduce perform functional reduction
• fsm extract and optimize finite state machines
• fsm_detect finding FSMs in design
• fsm_expand expand FSM cells by merging logic into it
• fsm_export exporting FSMs to KISS2 files
• fsm_extract extracting FSMs in design
• fsm_info print information on finite state machines
• fsm_map mapping FSMs to basic logic
• fsm_opt optimize finite state machines
• fsm_recode recoding finite state machines
• greenpak4_dffinv merge greenpak4 inverters and DFF/latches
• help display help messages
• hierarchy check, expand and clean up design hierarchy
• hilomap technology mapping of constant hi- and/or lo-drivers
• history show last interactive commands
• ice40_ffinit iCE40: handle FF init values
• ice40_ffssr iCE40: merge synchronous set/reset into FF cells
• ice40_opt iCE40: perform simple optimizations
• insbuf insert buffer cells for connected wires
• iopadmap technology mapping of i/o pads (or buffers)
• json write design in JSON format
• log print text and log files
• ls list modules or objects in modules
• ltp print longest topological path
• lut2mux convert $lut to $_MUX_
• maccmap mapping macc cells
• memory translate memories to basic cells
• memory_bram map memories to block rams
• memory_collect creating multi-port memory cells
• memory_dff merge input/output DFFs into memories
• memory_map translate multiport memories to basic cells
• memory_memx emulate vlog sim behavior for mem ports
• memory_nordff extract read port FFs from memories
• memory_share consolidate memory ports
• memory_unpack unpack multi-port memory cells
• miter automatically create a miter circuit
• muxcover cover trees of MUX cells with wider MUXes
• nlutmap map to LUTs of different sizes
• opt perform simple optimizations
• opt_clean remove unused cells and wires
• opt_demorgan Optimize reductions with DeMorgan equivalents
• opt_expr perform const folding and simple expression rewriting
• opt_merge consolidate identical cells
• opt_muxtree eliminate dead trees in multiplexer trees
• opt_reduce simplify large MUXes and AND/OR gates
• opt_rmdff remove DFFs with constant inputs
• plugin load and list loaded plugins
• pmuxtree transform $pmux cells to trees of $mux cells
• prep generic synthesis script
• proc translate processes to netlists
• proc_arst detect asynchronous resets
• proc_clean remove empty parts of processes
• proc_dff extract flip-flops from processes
• proc_dlatch extract latches from processes
• proc_init convert initial block to init attributes
• proc_mux convert decision trees to multiplexers
• proc_rmdead eliminate dead trees in decision trees
• qwp quadratic wirelength placer
• read load HDL designs
• read_blif read BLIF file
• read_ilang read modules from ilang file
• read_json read JSON file
• read_liberty read cells from liberty file
• read_verilog read modules from Verilog file
• rename rename object in the design
• rmports remove module ports with no connections
• sat solve a SAT problem in the circuit
• scatter add additional intermediate nets
• scc detect strongly connected components (logic loops)
• script execute commands from script file
• select modify and view the list of selected objects
• setattr set/unset attributes on objects
• setparam set/unset parameters on objects
• setundef replace undef values with defined constants
• share perform sat-based resource sharing
• shell enter interactive command mode
• show generate schematics using graphviz
• shregmap map shift registers
• sim simulate the circuit
• simplemap mapping simple coarse-grain cells
• splice create explicit splicing cells
• splitnets split up multi-bit nets
• stat print some statistics
• submod moving part of a module to a new submodule
• synth generic synthesis script
• synth_achronix synthesis for Acrhonix Speedster22i FPGAs.
• synth_coolrunner2 synthesis for Xilinx Coolrunner-II CPLDs
• synth_easic synthesis for eASIC platform
• synth_ecp5 synthesis for ECP5 FPGAs
• synth_gowin synthesis for Gowin FPGAs
• synth_greenpak4 synthesis for GreenPAK4 FPGAs
• synth_ice40 synthesis for iCE40 FPGAs
• synth_intel synthesis for Intel (Altera) FPGAs.
• synth_xilinx synthesis for Xilinx FPGAs
• tcl execute a TCL script file
• techmap generic technology mapper
• tee redirect command output to file
• test_abcloop automatically test handling of loops in abc command
• test_autotb generate simple test benches
• test_cell automatically test the implementation of a cell type
• torder print cells in topological order
• trace redirect command output to file
• tribuf infer tri-state buffers
• uniquify create unique copies of modules
• verific load Verilog and VHDL designs using Verific
• verilog_defaults set default options for read_verilog
• verilog_defines define and undefine verilog defines
• wreduce reduce the word size of operations if possible
• write_aiger write design to AIGER file
• write_blif write design to BLIF file
• write_btor write design to BTOR file
• write_edif write design to EDIF netlist file
• write_file write a text to a file
• write_firrtl write design to a FIRRTL file
• write_ilang write design to ilang file
• write_intersynth write design to InterSynth netlist file
• write_json write design to a JSON file
• write_simplec convert design to simple C code
• write_smt2 write design to SMT-LIBv2 file
• write_smv write design to SMV file
• write_spice write design to SPICE netlist file
• write_table write design as connectivity table
• write_verilog write design to Verilog file
• zinit add inverters so all FF are zero-initialized 

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Source:
Yosys HQ / Yosys Open SYnthesis Suite

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