From: Aleks-Daniel Jakimenko-Aleksejev Date: Sat, 19 Nov 2016 16:34:13 +0000 (+0200) Subject: Markdownify README even further X-Git-Tag: yosys-0.8~581^2~1 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=751ad3c6180ad5180a163e263dfcdebc38683a1b;p=yosys.git Markdownify README even further --- diff --git a/README.md b/README.md index 0517f9253..adb639b8d 100644 --- a/README.md +++ b/README.md @@ -47,7 +47,7 @@ Getting Started 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. +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: @@ -87,8 +87,8 @@ 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: +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 @@ -104,16 +104,16 @@ elaborate design hierarchy: yosys> hierarchy -convert processes ("always" blocks) to netlist elements and perform +convert processes (``always`` blocks) to netlist elements and perform some simple optimizations: yosys> proc; opt -display design netlist using xdot: +display design netlist using ``xdot``: yosys> show -the same thing using 'gv' as postscript viewer: +the same thing using ``gv`` as postscript viewer: yosys> show -format ps -viewer gv @@ -165,7 +165,7 @@ The following very basic synthesis script should work well with all designs: 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 +in the liberty file ``mycells.lib``, the following synthesis script will synthesize for the given cell library: # the high-level stuff @@ -184,7 +184,7 @@ for the given cell library: 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. +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: @@ -192,8 +192,8 @@ 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 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 @@ -218,11 +218,11 @@ 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 ``tri``, ``triand``, ``trior``, ``wand`` and ``wor`` net types -- The "config" keyword and library map files +- The ``config`` keyword and library map files -- The "disable", "primitive" and "specify" statements +- The ``disable``, ``primitive`` and ``specify`` statements - Latched logic (is synthesized as logic with feedback loops) @@ -230,70 +230,70 @@ for them: Verilog Attributes and non-standard features ============================================ -- The 'full_case' attribute on case statements is supported - (also the non-standard "// synopsys full_case" directive) +- 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 ``parallel_case`` attribute on case statements is supported + (also the non-standard ``// synopsys parallel_case`` directive) -- The "// synopsys translate_off" and "// synopsys translate_on" +- 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 +- 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 +- 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 +- 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 +- 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 +- 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 onehot state register. This +- The ``onehot`` attribute on wires mark them as onehot 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 +- 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 "keep" attribute on cells and wires is used to mark objects that should +- 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 + 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" +- 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 +- 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 +- 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 +- 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. @@ -306,7 +306,7 @@ Verilog Attributes and non-standard features 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 +- 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. @@ -320,7 +320,7 @@ Verilog Attributes and non-standard features assign b = 42; """ -- The attribute "via_celltype" can be used to implement a Verilog task or +- 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. @@ -348,9 +348,9 @@ Verilog Attributes and non-standard features 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 + (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: + a plugin alias using the ``:`` syntax. For example: module dpitest; import "DPI-C" function foo:round = real my_round (real); @@ -359,11 +359,11 @@ Verilog Attributes and non-standard features $ yosys -p 'plugin -a foo -i /lib/libm.so; read_verilog dpitest.v' -- Sized constants (the syntax 's?[bodh]) support constant +- 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 + must be put in parentheses. Examples: ``WIDTH'd42``, ``(4+2)'b101010`` -- The system tasks $finish and $display are supported in initial blocks +- The system tasks ``$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. @@ -371,42 +371,42 @@ Verilog Attributes and non-standard features Non-standard or SystemVerilog features for formal verification ============================================================== -- Support for "assert", "assume", and "restrict" is enabled when - read_verilog is called with -formal. +- Support for ``assert``, ``assume``, and ``restrict`` is enabled when + ``read_verilog`` is called with ``-formal``. -- The system task $initstate evaluates to 1 in the initial state and +- The system task ``$initstate`` evaluates to 1 in the initial state and to 0 otherwise. -- The system task $anyconst evaluates to any constant value. +- The system task ``$anyconst`` evaluates to any constant value. -- The system task $anyseq evaluates to any value, possibly a different +- The system task ``$anyseq`` evaluates to any value, possibly a different value in each cycle. -- The SystemVerilog tasks $past, $stable, $rose and $fell are supported +- The SystemVerilog tasks ``$past``, ``$stable``, ``$rose`` and ``$fell`` are supported in any clocked block. -- The syntax @($global_clock) can be used to create FFs that have no +- The syntax ``@($global_clock)`` can be used to create FFs that have no explicit clock input ($ff cells). Supported features from SystemVerilog ===================================== -When read_verilog is called with -sv, it accepts some language features +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 ``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" and "restrict" statements from SystemVerilog are also - supported. The same limitations as with the "assert" statement apply. +- The ``assume`` and ``restrict`` 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. +- The keywords ``always_comb``, ``always_ff`` and ``always_latch``, ``logic`` and + ``bit`` are supported. - SystemVerilog packages are supported. Once a SystemVerilog file is read - into a design with "read_verilog", all its packages are available to + into a design with ``read_verilog``, all its packages are available to SystemVerilog files being read into the same design afterwards.