yosys -- Yosys Open SYnthesis Suite

Copyright (C) 2012 - 2019  Clifford Wolf <clifford@clifford.at>

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yosys – Yosys Open SYnthesis Suite

This is a framework for RTL synthesis tools. It currently has
extensive Verilog-2005 support and provides a basic set of
synthesis algorithms for various application domains.

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).

Web Site and Other Resources

More information and documentation can be found on the Yosys web site:

http://www.clifford.at/yosys/

The "Documentation" page on the web site contains links to more resources,
including a manual that even describes some of the Yosys internals:

http://www.clifford.at/yosys/documentation.html

The file CodingReadme in this directory contains additional information
for people interested in using the Yosys C++ APIs.

Users interested in formal verification might want to use the formal verification
front-end for Yosys, SymbiYosys:

Setup

You need a C++ compiler with C++11 support (up-to-date CLANG or GCC is
recommended) and some standard tools such as GNU Flex, GNU Bison, and GNU Make.
TCL, readline and libffi are optional (see ENABLE_* settings in Makefile).
Xdot (graphviz) is used by the show command in yosys to display schematics.

For example on Ubuntu Linux 16.04 LTS the following commands will install all
prerequisites for building yosys:

$ sudo apt-get install build-essential clang bison flex \
	libreadline-dev gawk tcl-dev libffi-dev git \
	graphviz xdot pkg-config python3 libboost-system-dev \
	libboost-python-dev libboost-filesystem-dev zlib1g-dev

Similarily, on Mac OS X Homebrew can be used to install dependencies (from within cloned yosys repository):

$ brew tap Homebrew/bundle && brew bundle

or MacPorts:

$ sudo port install bison flex readline gawk libffi \
	git graphviz pkgconfig python36 boost zlib tcl

On FreeBSD use the following command to install all prerequisites:

# pkg install bison flex readline gawk libffi\
	git graphviz pkgconf python3 python36 tcl-wrapper boost-libs

On FreeBSD system use gmake instead of make. To run tests use:
% MAKE=gmake CC=cc gmake test

For Cygwin use the following command to install all prerequisites, or select these additional packages:

setup-x86_64.exe -q --packages=bison,flex,gcc-core,gcc-g++,git,libffi-devel,libreadline-devel,make,pkg-config,python3,tcl-devel,boost-build,zlib-devel

There are also pre-compiled Yosys binary packages for Ubuntu and Win32 as well
as a source distribution for Visual Studio. Visit the Yosys download page for
more information: http://www.clifford.at/yosys/download.html

To configure the build system to use a specific compiler, use one of

$ make config-clang
$ make config-gcc

For other compilers and build configurations it might be
necessary to make some changes to the config section of the
Makefile.

$ vi Makefile            # ..or..
$ vi Makefile.conf

To build Yosys simply type 'make' in this directory.

$ make
$ sudo make install

Note that this also downloads, builds and installs ABC (using yosys-abc
as executable name).

Tests are located in the tests subdirectory and can be executed using the test target. Note that you need gawk as well as a recent version of iverilog (i.e. build from git). Then, execute tests via:

$ make test

Getting Started

Yosys can be used with the interactive command shell, with
synthesis scripts or with command line arguments. Let's perform
a simple synthesis job using the interactive command shell:

$ ./yosys
yosys>

the command help can be used to print a list of all available
commands and help <command> to print details on the specified command:

yosys> help help

reading and elaborating the design using the Verilog frontend:

yosys> read -sv tests/simple/fiedler-cooley.v
yosys> hierarchy -top up3down5

writing the design to the console in Yosys's internal format:

yosys> write_ilang

convert processes (always blocks) to netlist elements and perform
some simple optimizations:

yosys> proc; opt

display design netlist using xdot:

yosys> show

the same thing using gv as postscript viewer:

yosys> show -format ps -viewer gv

translating netlist to gate logic and perform some simple optimizations:

yosys> techmap; opt

write design netlist to a new Verilog file:

yosys> write_verilog synth.v

or using a simple synthesis script:

$ cat synth.ys
read -sv tests/simple/fiedler-cooley.v
hierarchy -top up3down5
proc; opt; techmap; opt
write_verilog synth.v

$ ./yosys synth.ys

If ABC is enabled in the Yosys build configuration and a cell library is given
in the liberty file mycells.lib, the following synthesis script will
synthesize for the given cell library:

# read design
read -sv tests/simple/fiedler-cooley.v
hierarchy -top up3down5

# the high-level stuff
proc; 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

If you do not have a liberty file but want to test this synthesis script,
you can use the file examples/cmos/cmos_cells.lib from the yosys sources
as simple example.

Liberty file downloads for and information about free and open ASIC standard
cell libraries can be found here:

The command synth provides a good default synthesis script (see
help synth):

read -sv tests/simple/fiedler-cooley.v
synth -top up3down5

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

The command prep provides a good default word-level synthesis script, as
used in SMT-based formal verification.

Unsupported Verilog-2005 Features

The following Verilog-2005 features are not supported by
Yosys and there are currently no plans to add support
for them:

Non-synthesizable language features as defined in
IEC 62142(E):2005 / IEEE Std. 1364.1(E):2002
The tri, triand and trior net types
The config and disable keywords and library map files

Verilog Attributes and non-standard features

The full_case attribute on case statements is supported
(also the non-standard // synopsys full_case directive)
The parallel_case attribute on case statements is supported
(also the non-standard // synopsys parallel_case directive)
The // synopsys translate_off and // synopsys translate_on
directives are also supported (but the use of `ifdef .. `endif
is strongly recommended instead).
The nomem2reg attribute on modules or arrays prohibits the
automatic early conversion of arrays to separate registers. This
is potentially dangerous. Usually the front-end has good reasons
for converting an array to a list of registers. Prohibiting this
step will likely result in incorrect synthesis results.
The mem2reg attribute on modules or arrays forces the early
conversion of arrays to separate registers.
The nomeminit attribute on modules or arrays prohibits the
creation of initialized memories. This effectively puts mem2reg
on all memories that are written to in an initial block and
are not ROMs.
The nolatches attribute on modules or always-blocks
prohibits the generation of logic-loops for latches. Instead
all not explicitly assigned values default to x-bits. This does
not affect clocked storage elements such as flip-flops.
The nosync attribute on registers prohibits the generation of a
storage element. The register itself will always have all bits set
to 'x' (undefined). The variable may only be used as blocking assigned
temporary variable within an always block. This is mostly used internally
by Yosys to synthesize Verilog functions and access arrays.
The onehot attribute on wires mark them as one-hot state register. This
is used for example for memory port sharing and set by the fsm_map pass.
The blackbox attribute on modules is used to mark empty stub modules
that have the same ports as the real thing but do not contain information
on the internal configuration. This modules are only used by the synthesis
passes to identify input and output ports of cells. The Verilog backend
also does not output blackbox modules on default. read_verilog, unless
called with -noblackbox will automatically set the blackbox attribute
on any empty module it reads.
The noblackbox attribute set on an empty module prevents read_verilog
from automatically setting the blackbox attribute on the module.
The whitebox attribute on modules triggers the same behavior as
blackbox, but is for whitebox modules, i.e. library modules that
contain a behavioral model of the cell type.
The lib_whitebox attribute overwrites whitebox when read_verilog
is run in -lib mode. Otherwise it's automatically removed.
The dynports attribute is used by the Verilog front-end to mark modules
that have ports with a width that depends on a parameter.
The hdlname attribute is used by some passes to document the original
(HDL) name of a module when renaming a module.
The keep attribute on cells and wires is used to mark objects that should
never be removed by the optimizer. This is used for example for cells that
have hidden connections that are not part of the netlist, such as IO pads.
Setting the keep attribute on a module has the same effect as setting it
on all instances of the module.
The keep_hierarchy attribute on cells and modules keeps the flatten
command from flattening the indicated cells and modules.
The init attribute on wires is set by the frontend when a register is
initialized "FPGA-style" with reg foo = val. It can be used during
synthesis to add the necessary reset logic.
The top attribute on a module marks this module as the top of the
design hierarchy. The hierarchy command sets this attribute when called
with -top. Other commands, such as flatten and various backends
use this attribute to determine the top module.
The src attribute is set on cells and wires created by to the string
<hdl-file-name>:<line-number> by the HDL front-end and is then carried
through the synthesis. When entities are combined, a new, -separated
string is created that contains all the string from the original entities.
The defaultvalue attribute is used to store default values for
module inputs. The attribute is attached to the input wire by the HDL
front-end when the input is declared with a default value.
The parameter and localparam attributes are used to mark wires
that represent module parameters or localparams (when the HDL front-end
is run in -pwires mode).
Wires marked with the hierconn attribute are connected to wires with the
same name (format cell_name.identifier) when they are imported from
sub-modules by flatten.
The clkbuf_driver attribute can be set on an output port of a blackbox
module to mark it as a clock buffer output, and thus prevent clkbufmap
from inserting another clock buffer on a net driven by such output.
The clkbuf_sink attribute can be set on an input port of a module to
request clock buffer insertion by the clkbufmap pass.
The clkbuf_inv attribute can be set on an output port of a module
with the value set to the name of an input port of that module. When
the clkbufmap would otherwise insert a clock buffer on this output,
it will instead try inserting the clock buffer on the input port (this
is used to implement clock inverter cells that clock buffer insertion
will "see through").
The clkbuf_inhibit is the default attribute to set on a wire to prevent
automatic clock buffer insertion by clkbufmap. This behaviour can be
overridden by providing a custom selection to clkbufmap.
The invertible_pin attribute can be set on a port to mark it as
invertible via a cell parameter. The name of the inversion parameter
is specified as the value of this attribute. The value of the inversion
parameter must be of the same width as the port, with 1 indicating
an inverted bit and 0 indicating a non-inverted bit.
The iopad_external_pin attribute on a blackbox module's port marks
it as the external-facing pin of an I/O pad, and prevents iopadmap
from inserting another pad cell on it.
The module attribute abc9_box_id specifies a positive integer linking a
blackbox or whitebox definition to a corresponding entry in a abc9
box-file.
The port attribute abc9_carry marks the carry-in (if an input port) and
carry-out (if output port) ports of a box. This information is necessary for
abc9 to preserve the integrity of carry-chains. Specifying this attribute
onto a bus port will affect only its most significant bit.
The output port attribute abc9_arrival specifies an integer, or a string
of space-separated integers to be used as the arrival time of this blackbox
port. It can be used, for example, to specify the clk-to-Q delay of a flip-
flop output for consideration during abc9 techmapping.
The input port attribute abc9_required specifies an integer, or a string
of space-separated integers to be used as the required time of this blackbox
port. It can be used, for example, to specify the setup-time of a flip-flop
input for consideration during abc9 techmapping.
The module attribute abc9_flop is a boolean marking the module as a
flip-flop. This allows abc9 to analyse its contents in order to perform
sequential synthesis.
The frontend sets attributes always_comb, always_latch and
always_ff on processes derived from SystemVerilog style always blocks
according to the type of the always. These are checked for correctness in
proc_dlatch.
The cell attribute wildcard_port_conns represents wildcard port
connections (SystemVerilog .*). These are resolved to concrete
connections to matching wires in hierarchy.
In addition to the (* ... *) attribute syntax, Yosys supports
the non-standard {* ... *} attribute syntax to set default attributes
for everything that comes after the {* ... *} statement. (Reset
by adding an empty {* *} statement.)
In module parameter and port declarations, and cell port and parameter
lists, a trailing comma is ignored. This simplifies writing Verilog code
generators a bit in some cases.
Modules can be declared with module mod_name(...); (with three dots
instead of a list of module ports). With this syntax it is sufficient
to simply declare a module port as 'input' or 'output' in the module
body.
When defining a macro with `define, all text between triple double quotes
is interpreted as macro body, even if it contains unescaped newlines. The
triple double quotes are removed from the macro body. For example:
```
`define MY_MACRO(a, b) """
   assign a = 23;
   assign b = 42;
"""
```
The attribute via_celltype can be used to implement a Verilog task or
function by instantiating the specified cell type. The value is the name
of the cell type to use. For functions the name of the output port can
be specified by appending it to the cell type separated by a whitespace.
The body of the task or function is unused in this case and can be used
to specify a behavioral model of the cell type for simulation. For example:
```
module my_add3(A, B, C, Y);
  parameter WIDTH = 8;
  input [WIDTH-1:0] A, B, C;
  output [WIDTH-1:0] Y;
  ...
endmodule

module top;
  ...
  (* via_celltype = "my_add3 Y" *)
  (* via_celltype_defparam_WIDTH = 32 *)
  function [31:0] add3;
    input [31:0] A, B, C;
    begin
      add3 = A + B + C;
    end
  endfunction
  ...
endmodule
```
A limited subset of DPI-C functions is supported. The plugin mechanism
(see help plugin) can be used to load .so files with implementations
of DPI-C routines. As a non-standard extension it is possible to specify
a plugin alias using the <alias>: syntax. For example:
```
module dpitest;
  import "DPI-C" function foo:round = real my_round (real);
  parameter real r = my_round(12.345);
endmodule

$ yosys -p 'plugin -a foo -i /lib/libm.so; read_verilog dpitest.v'
```
Sized constants (the syntax <size>'s?[bodh]<value>) support constant
expressions as <size>. If the expression is not a simple identifier, it
must be put in parentheses. Examples: WIDTH'd42, (4+2)'b101010
The system tasks $finish, $stop and $display are supported in
initial blocks in an unconditional context (only if/case statements on
expressions over parameters and constant values are allowed). The intended
use for this is synthesis-time DRC.
There is limited support for converting specify .. endspecify
statements to special $specify2, $specify3, and $specrule cells,
for use in blackboxes and whiteboxes. Use read_verilog -specify to
enable this functionality. (By default these blocks are ignored.)

Non-standard or SystemVerilog features for formal verification

Support for assert, assume, restrict, and cover is enabled
when read_verilog is called with -formal.
The system task $initstate evaluates to 1 in the initial state and
to 0 otherwise.
The system function $anyconst evaluates to any constant value. This is
equivalent to declaring a reg as rand const, but also works outside
of checkers. (Yosys also supports rand const outside checkers.)
The system function $anyseq evaluates to any value, possibly a different
value in each cycle. This is equivalent to declaring a reg as rand,
but also works outside of checkers. (Yosys also supports rand
variables outside checkers.)
The system functions $allconst and $allseq can be used to construct
formal exist-forall problems. Assumptions only hold if the trace satisfies
the assumption for all $allconst/$allseq values. For assertions and cover
statements it is sufficient if just one $allconst/$allseq value triggers
the property (similar to $anyconst/$anyseq).
Wires/registers declared using the anyconst/anyseq/allconst/allseq attribute
(for example (* anyconst *) reg [7:0] foobar;) will behave as if driven
by a $anyconst/$anyseq/$allconst/$allseq function.
The SystemVerilog tasks $past, $stable, $rose and $fell are
supported in any clocked block.
The syntax @($global_clock) can be used to create FFs that have no
explicit clock input ($ff cells). The same can be achieved by using
@(posedge <netname>) or @(negedge <netname>) when <netname>
is marked with the (* gclk *) Verilog attribute.

Supported features from SystemVerilog

When read_verilog is called with -sv, it accepts some language features
from SystemVerilog:

The assert statement from SystemVerilog is supported in its most basic
form. In module context: assert property (<expression>); and within an
always block: assert(<expression>);. It is transformed to an $assert cell.
The assume, restrict, and cover statements from SystemVerilog are
also supported. The same limitations as with the assert statement apply.
The keywords always_comb, always_ff and always_latch, logic
and bit are supported.
Declaring free variables with rand and rand const is supported.
Checkers without a port list that do not need to be instantiated (but instead
behave like a named block) are supported.
SystemVerilog packages are supported. Once a SystemVerilog file is read
into a design with read_verilog, all its packages are available to
SystemVerilog files being read into the same design afterwards.
typedefs are supported (including inside packages)
SystemVerilog interfaces (SVIs) are supported. Modports for specifying whether
ports are inputs or outputs are supported.

Building the documentation

Note that there is no need to build the manual if you just want to read it.
Simply download the PDF from http://www.clifford.at/yosys/documentation.html
instead.

On Ubuntu, texlive needs these packages to be able to build the manual:

sudo apt-get install texlive-binaries
sudo apt-get install texlive-science      # install algorithm2e.sty
sudo apt-get install texlive-bibtex-extra # gets multibib.sty
sudo apt-get install texlive-fonts-extra  # gets skull.sty and dsfont.sty
sudo apt-get install texlive-publishers   # IEEEtran.cls

Also the non-free font luximono should be installed, there is unfortunately
no Ubuntu package for this so it should be installed separately using
getnonfreefonts:

wget https://tug.org/fonts/getnonfreefonts/install-getnonfreefonts
sudo texlua install-getnonfreefonts # will install to /usr/local by default, can be changed by editing BINDIR at MANDIR at the top of the script
getnonfreefonts luximono # installs to /home/user/texmf

Then execute, from the root of the repository:

make manual

Notes:

To run make manual you need to have installed Yosys with make install,
otherwise it will fail on finding kernel/yosys.h while building
PRESENTATION_Prog.

名称与所有者	YosysHQ/yosys
主编程语言	C++
编程语言	C++ (语言数: 20)
平台
许可证	ISC License

创建于	2013-01-05 18:10:48
推送于	2025-11-04 21:09:42
最后一次提交
发布数	59
最新版本名称	v0.58 (发布于 2025-10-08 13:52:03)
第一版名称	yosys-0.2.0 (发布于 )

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