``` yosys -- Yosys Open SYnthesis Suite Copyright (C) 2012 - 2018 Clifford Wolf Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies. THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. ``` 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: - https://symbiyosys.readthedocs.io/en/latest/ - https://github.com/YosysHQ/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 Similarily, on Mac OS X MacPorts or Homebrew can be used to install dependencies: $ brew tap Homebrew/bundle && brew bundle $ sudo port install bison flex readline gawk libffi \ git graphviz pkgconfig python36 On FreeBSD use the following command to install all prerequisites: # pkg install bison flex readline gawk libffi\ git graphviz pkgconfig python3 python36 tcl-wrapper 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 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 `` to print details on the specified command: yosys> help help reading the design using the Verilog frontend: yosys> read_verilog tests/simple/fiedler-cooley.v writing the design to the console in Yosys's internal format: yosys> write_ilang elaborate design hierarchy: yosys> hierarchy 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 a similar synthesis can be performed using yosys command line options only: $ ./yosys -o synth.v -p hierarchy -p proc -p opt \ -p techmap -p opt tests/simple/fiedler-cooley.v or using a simple synthesis script: $ cat synth.ys read_verilog tests/simple/fiedler-cooley.v hierarchy; proc; opt; techmap; opt write_verilog synth.v $ ./yosys synth.ys It is also possible to only have the synthesis commands but not the read/write commands in the synthesis script: $ cat synth.ys hierarchy; proc; opt; techmap; opt $ ./yosys -o synth.v tests/simple/fiedler-cooley.v synth.ys The following very basic synthesis script should work well with all designs: # check design hierarchy hierarchy # translate processes (always blocks) proc; opt # detect and optimize FSM encodings fsm; opt # implement memories (arrays) memory; opt # convert to gate logic techmap; opt 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: # the high-level stuff hierarchy; 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. Liberty file downloads for and information about free and open ASIC standard cell libraries can be found here: - http://www.vlsitechnology.org/html/libraries.html - http://www.vlsitechnology.org/synopsys/vsclib013.lib The command ``synth`` provides a good default synthesis script (see ``help synth``). If possible a synthesis script should borrow from ``synth``. For example: # the high-level stuff hierarchy synth -run coarse # mapping to internal cells techmap; opt -fast dfflibmap -liberty mycells.lib abc -liberty mycells.lib clean Yosys is under construction. A more detailed documentation will follow. 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``, ``trior``, ``wand`` and ``wor`` net types - The ``config`` keyword and library map files - The ``disable``, ``primitive`` and ``specify`` statements - Latched logic (is synthesized as logic with feedback loops) 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. - 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 ``:`` 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. - 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 tipple 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 ``:`` 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 ``'s?[bodh]``) support constant expressions as . If the expression is not a simple identifier, it must be put in parentheses. Examples: ``WIDTH'd42``, ``(4+2)'b101010`` - The system tasks ``$finish`` and ``$display`` are supported in initial blocks in an unconditional context (only if/case statements on parameters and constant values). The intended use for this is synthesis-time DRC. 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 )`` or ``@(negedge )`` when ```` 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 ();`` and within an always block: ``assert();``. It is transformed to a $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. - 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`.