Netlist Format ¶

The output from the parse and elaboration steps is a “netlist” rooted in a Design object. Parsing translates the design described in the initial source file into a temporary symbolic “pform”. Elaboration then expands the design, resolving references and expanding hierarchies, to produce a flattened netlist. This is the form that optimizers and code generators use.

The design optimization processes all manipulate the netlist, translating it to a (hopefully) better netlist after each step. The complete netlist is then passed to the code generator, the emit function, where the final code (in the target format) is produced.

Structural Items: NetNode and NetNet ¶

Components and wires, memories and registers all at their base are either NetNode objects or NetNet objects. Even these classes are derived from the NetObj class.

All NetNode and NetNet objects have a name and some number of pins. The name usually comes from the Verilog source that represents that object, although objects that are artifacts of elaboration will have a generated (and probably unreadable) name. The pins are the ports into the device. NetNode objects have a pin for each pin of the component it represents, and NetNet objects have a pin for each signal in the vector.

Node and net pins can be connected together via the connect function. Connections are transitive (A==B and B==c means A==C) so connections accumulate on a link as items are connected to it. The destructors for nets and nodes automatically arrange for pins to be disconnected when the item is deleted, so that the netlist can be changed during processing.

Structural Links ¶

The NetNode and NetNet classes contain arrays of Link objects, one object per pin. Each pin is a single bit. The Link objects link to all the NetNode and NetNet objects’ links that are connected together in the design, and to a Nexus object. This way, code that examines a node of the design can discover what is connected to each pin.

The connected set of links also has common properties that are stored or access from the Nexus object. All the Links that are connected together are also connected to a single Nexus object. This object is useful for accessing the properties and values that come from the connected set of links. The Nexus object is also handy for iterating over the connected set of Links.

See the Link class definition in netlist.h for a description of the link methods, and the Nexus class for nexus global methods.

Currently, a link has 3 possible direction properties:

PASSIVE – These pins are sampled by the object that holds the pin based on some external event. These are used, for example, by NetESignal objects that read a point for a procedural expression. INPUT – These pins potentially react to the setting of its input. OUTPUT – These pins potentially drive the node. (They may be three-state.)

Behavioral Items: NetProcTop, NetProc and derived classes ¶

Behavioral items are not in general linked to the netlist. Instead, they represent elaborated behavioral statements. The type of the object implies what the behavior of the statement does. For example, a NetCondit object represents an if statement, and carries a condition expression and up to two alternative sub-statements.

At the root of a process is a NetProcTop object. This class carries a type flag (initial or always) and a single NetProc object. The contained statement may, depending on the derived class, refer to other statements, compound statements, so on. But at the root of the tree is the NetProcTop object. The Design class keeps a list of the elaborated NetProcTop objects. That list represents the list of processes in the design.

Interaction Of Behavioral And Structural: NetAssign_ ¶

The behavioral statements in a Verilog design effect the structural aspects through assignments to registers. Registers are structural items represented by the NetNet class, linked to the assignment statement through pins. This implies that the l-value of an assignment is structural. It also implies that the statement itself is structural, and indeed it is derived from NetNode.

The NetAssign_ class is also derived from the NetProc class because what it does is brought on by executing the process. By multiple inheritance we have therefore that the assignment is both a NetNode and a NetProc. The NetAssign_ node has pins that represent the l-value of the statement, and carries behavioral expressions that represent the r-value of the assignment.

The netlist form includes the NetMemory type to hold the content of a memory. Instances of this type represent the declaration of a memory, and occur once for each memory. References to the memory are managed by the NetEMemory and NetAssignMem_ classes.

An instance of the NetEMemory class is created whenever a procedural expression references a memory element. The operand is the index to use to address (and read) the memory.

An instance of the NetAssignMem_ class is created when there is a procedural assignment to the memory. The NetAssignMem_ object represents the l-value reference (a write) to the memory. As with the NetEMemory class, this is a procedural reference only.

When a memory reference appears in structural context (i.e. continuous assignments) elaboration creates a NetRamDq. This is a LPM_RAM_DQ device. Elaboration leaves the write control and data input pins unconnected for now, because memories cannot appear is l-values of continuous assignments. However, the synthesis functor may connect signals to the write control lines to get a fully operational RAM.

By the time elaboration completes, there may be many NetAssignMem_, NetEMemory and NetRamDq objects referencing the same NetMemory object. Each represents a port into the memory. It is up to the synthesis steps (and the target code) to figure out what to do with these ports.

Expressions ¶

Expressions are represented as a tree of NetExpr nodes. The NetExpr base class contains the core methods that represent an expression node, including virtual methods to help with dealing with nested complexities of expressions.

Expressions (as expressed in the source and p-form) may also be elaborated structurally, where it makes sense. For example, assignment l-value expressions are represented as connections to pins. Also, continuous assignment module items are elaborated as gates instead of as a procedural expression. Event expressions are also elaborated structurally as events are like devices that trigger behavioral statements.

However, typical expressions the behavioral description are represented as a tree of NetExpr nodes. The derived class of the node encodes what kind of operator the node represents.

Expression Bit Width ¶

The expression (represented by the NetExpr class) has a bit width that it either explicitly specified, or implied by context or contents. When each node of the expression is first constructed during elaboration, it is given, by type and parameters, an idea what its width should be. It certain cases, this is definitive, for example with signals. In others, it is ambiguous, as with unsized constants.

As the expression is built up by elaboration, operators that combine expressions impose bit widths of the environment or expose the bit widths of the sub expressions. For example, the bitwise AND (&) operator has a bit size implied by its operands, whereas the comparison (==) operator has a bit size of 1. The building up of the elaborated expression checks and adjusts the bit widths as the expression is built up, until finally the context of the expression takes the final bit width and makes any final adjustments.

The NetExpr::expr_width() method returns the calculated (or guessed) expression width. This method will return 0 until the width is set by calculation or context. If this method returns false, then it is up to the context that wants the width to set one. The elaboration phase will call the NetExpr::set_width method on an expression as soon as it gets to a point where it believes that it knows what the width should be.

The NetExpr::set_width(unsigned) virtual method is used by the context of an expression node to note to the expression that the width is determined and please adapt. If the expression cannot reasonably adapt, it will return false. Otherwise, it will adjust bit widths and return true.

Interaction Of Expressions And Structure: NetESignal ¶

The NetAssign_ class described above is the means for processes to manipulate the net, but values are read from the net by NetESignal objects. These objects are class NetExpr because they can appear in expressions (and have width). They are not NetNode object, but hold pointers to a NetNet object, which is used to retrieve values with the expression is evaluated.

Hierarchy In Netlists ¶

The obvious hierarchical structure of Verilog is the module. The Verilog program may contain any number of instantiations of modules in order to form an hierarchical design. However, the elaboration of the design into a netlist erases module boundaries. Modules are expanded each place they are used, with the hierarchical instance name used to name the components of the module instance. However, the fact that a wire or register is a module port is lost.

The advantage of this behavior is first the simplification of the netlist structure itself. Backends that process netlists only need to cope with a list of nets, a list of nodes and a list of processes. This eases the task of the backend code generators.

Another advantage of this flattening of the netlist is that optimizers can operate globally, with optimizations freely crossing module boundaries. This makes coding of netlist transform functions such as constant propagation more effective and easier to write.

Scope Representation In Netlists ¶

In spite of the literal flattening of the design, scope information is preserved in the netlist, with the NetScope class. The Design class keeps a single pointer to the root scope of the design. This is the scope of the root module. Scopes that are then created within that (or any nested) module are placed as children of the root scope, and those children can have further children, and so on.

Each scope in the tree carries its own name, and its relationship to its parent and children. This makes it possible to walk the tree of scopes. In practice, the walking of the scopes is handled by recursive methods.

Each scope also carries the parameters that are applicable to the scope itself. The parameter expression (possibly evaluated) can be located by name, given the scope object itself. The scan of the pform to generate scopes also places the parameters that are declared in the scope. Overrides are managed during the scan, and once the scan is complete, defparam overrides are applied.

Tasks In Netlists ¶

The flattening of the design does not include tasks and named begin-end blocks. Tasks are behavioral hierarchy (whereas modules are structural) so do not easily succumb to the flattening process. In particular, it is logically impossible to flatten tasks that recurse. (The elaboration process does reserve the right to flatten some task calls. C++ programmers recognize this as inlining a task.)

Time Scale In Netlists ¶

The Design class and the NetScope classes carry time scale and resolution information of the elaborated design. There is a global resolution, and there are scope specific units and resolutions. Units and resolutions are specified as signed integers, and interpreted as the power of 10 of the value. For example, a resolution “-9” means that “1” is 1ns (1e-9). The notation supports units from -128 to +127. It is up to the back-ends to interpret “-4” as “100us”.

Delays are expressed in the netlist by integers. The units of these delays are always given in the units of the design precision. This allows everything to work with integers, and generally places the burden of scaling delays into elaboration. This is, after all, a common task. The Design::get_precision() method gets the global design precision.

Each NetScope also carries its local time_units and time_precision values. These are filled in during scope elaboration and are used in subsequent elaboration phases to arrange for scaling of delays. This information can also be used by the code generator to scale times back to the units of the scope, if that is desired.

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why after synthesis have assign?

  • Thread starter stormwolf
  • Start date Feb 1, 2005
  • Feb 1, 2005

Advanced Member level 4

synthesis assign After i synthesis a chip, and generate a netlist. I read the netlist find at netlist have "assign" command . Don't the "assign" effect backend tools such as astro?  

Newbie level 5

dc synthesis remove assigns If you don't fix assign, the astro may fail to pass drc. There are many articles to explain in solvnet, though they may not take effect as you expect in fact. You can write a script to modify the netlist.  

Advanced Member level 3

set_fix_multiple_port_nets Sometimes synopsys gives "assign" statement in its output codes, for example, when it need to convert one data type from wire to reg. Those assign statement can cause problem in both VerilogIn and Silicon Ensemble. NSC has codes to remove those lines, however, it results in connections broken, and you'll have to fix that somehow. To tell synopsys NOT using assign statement, do the following in dc_shell (command window in design_analyzer): 1. verilogout_no_tri=true 2. set_fix_multiple_port_nets -all -buffer_constants use man to see manuals of those variables.  

Advanced Member level 2

assign synthesis use this "set_fix_multiple_port_nets -all -buffer_constants -feedthroughs" before compile , your problem will solved.  

  • Feb 3, 2005

omid219

assign in netlist use this command, it will prevent adding assign in your netlist. set verilogout_equation false  

Full Member level 2

synopsys assign I found sometimes, it also works: change_name -rule verilog You can try... This just fix those assigns except feedthrough...  

  • Feb 10, 2005

Full Member level 4

remove assign dc_shell Sometimes if your codes have some error, the DC compile the codes failed. This will generate assign in your netlist even you have use "set_fix_multiple_port_nets -all -buffer_constants". So don't forget to check your RTL codes.  

Full Member level 1

set_dont_touch_network assign Hello! Why is it happen (these assigns) if I have used the commands above in version 2003.03 (here the assigns dissappear) and with the same settings in 200.06 I still get "assigns". Could be because of the DC version? Thanks in advance!  

  • Feb 15, 2005

Full Member level 6

assign statements in netlist hi, yes, after you used all above command, you will still find assign in your netlist. the only way you can do in synthesis is to compile -inc for several times. maybe you can get a good netlist. And maybe you can try rtlcompiler from c@dence. And if you dont want to do that ugly job , you can use p&r tools socencounter and setAssignbuf 1, and you can work around it. Best Regards.  

  • Feb 17, 2005
linuxluo said: hi, yes, after you used all above command, you will still find assign in your netlist. the only way you can do in synthesis is to compile -inc for several times. maybe you can get a good netlist. And maybe you can try rtlcompiler from c@dence. And if you dont want to do that ugly job , you can use p&r tools socencounter and setAssignbuf 1, and you can work around it. Best Regards. Click to expand...
  • Dec 23, 2005

Newbie level 1

fix multiple ports nets maybe you can check if you "set_dont_touch_network" on that net.  

  • Dec 25, 2005

Full Member level 3

assign statement in netlist after using set_fix_multiple_ports, assigns might be there. because that assigns logic is in the submodules. using scripts only we need to remove the assigns.  

  • Dec 28, 2005

cfriend

avoid verilog assign after synthesis If you use dc to synthesis, you can use : verilogout_no_tri=true set_fix_multiple_port_nets -all -buffer_constants not only before compile, but also use them before write netlist .  

  • Dec 29, 2005

assign con synopsys Can this assign be avoided by good coding style?  

  • Jan 2, 2006

Advanced Member level 1

remove assign dc check your design, If theree are the floating post in your module, The assign staements will are written in to the netlist  

  • Jan 5, 2006

verilogout_equation Hi, Don't get over react in removing assign. All the backend tool I know can accept this. First, I can think of two reasons why assign is present: 1. A net is driving two output ports. While Verilog support this, alot of other tools (e.g. schematic capture) do not support it (due to the net connect to the output port should be named the name of the port, so we end up with a net with 2 different names, which is bad). 2. A input port connect directly to an output port. For 1, the tool should insert a buffer to remove the assign. For 2, which it is possible to also insert a buffer to remove the assign, it is not productive. Depend on the coding style (and sometime due to parameterized design), alot of buffer may be needed. Some details on (2). There is almost no way to code in verilog that has a connection between an input port to an output port without using assign statement. The closest I know is: module abc (A, A); inout A; endmodule. Verilog supports connection in the port list (Cadence netlist using this for bus ripper). However, the above example is bi-directional, but assign is uni-directional. Don't try to use the above syntax; alot of tool will go burst. Regards, Eng Han www.eda-utilities.com  

  • Jan 7, 2006

Newbie level 4

synplify assigns in netlist Hi leeenghan & all, Thanks for the brief notes on why synthsis tool inserts assigns statements and various views i was not able to understand how iur going to avoid a net with 2 different names, which is bad by adding buffer thanks  

Member level 2

synopsys assign DC 2004.12 has bug, can not remove the assign in the generated netlist, 0406 can do  

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Verilog::Netlist::ContAssign - ContAssign assignment

DESCRIPTION

A Verilog::Netlist::ContAssign object is created by Verilog::Netlist for every continuous assignment statement in the current module.

See also Verilog::Netlist::Subclass for additional accessors and methods.

Keyword used to declare the assignment. Currently "assign" is the only supported value.

Left hand side of the assignment.

Pointer to the module the cell is in.

Reference to the Verilog::Netlist the cell is under.

Right hand side of the assignment.

MEMBER FUNCTIONS

Prints debugging information for this cell.

DISTRIBUTION

Verilog-Perl is part of the https://www.veripool.org/ free Verilog EDA software tool suite. The latest version is available from CPAN and from https://www.veripool.org/verilog-perl .

Copyright 2000-2024 by Wilson Snyder. This package is free software; you can redistribute it and/or modify it under the terms of either the GNU Lesser General Public License Version 3 or the Perl Artistic License Version 2.0.

Wilson Snyder <[email protected]>

Verilog-Perl , Verilog::Netlist::Subclass Verilog::Netlist

Module Install Instructions

To install Verilog::Std, copy and paste the appropriate command in to your terminal.

For more information on module installation, please visit the detailed CPAN module installation guide .

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A standalone structural (gate-level) verilog parser

xtofalex/naja-verilog

Folders and files, repository files navigation, naja-verilog.

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Introduction

Naja-Verilog is a structural (gate-level) Verilog parser and can be used to read synthesis generated netlists.

This library provides a verilog interface to Naja SNL , however both projects are not tied and naja-verilog can be integrated in any project needing structural verilog support.

💁 If you have any questions, bug to report or request, please open an issue or send me a mail .

⭐ If you find Naja-Verilog interesting, and would like to stay up-to-date, consider starring this repo to help spread the word.

Acknowledgement

verilog netlist assign

This project is supported and funded by NLNet through the NGI0 Entrust Fund.

Gate level netlist

This parser is dedicated to a very small part of verilog : the subset allowing to describe hierarchical gate level netlists. This is the format found at the output of synthesis tools such as Yosys .

To parse complete RTL level verilog or system verilog, please use projects such as: Verible . Apart the language support, the main difference with such RTL level parsing systems is that naja-verilog does not construct any AST but allows to construct the netlist on the fly while visiting the verilog source. Purpose is to reduce memory footprint and accelerate parsing time.

A comparable project can be found here: Parser-Verilog .

Compilation

Getting sources, dependencies.

Mandatory dependencies:

  • cmake : at least 3.22 version.

Embedded dependencies, through git sub module: google test .

Using nix-shell:

Building and Installing

Create your own parser.

Best starting point is to copy existing examples/implementations:

  • NajaVerilogSnippet : very simple snippet application verbosely printing visited objects.
  • VerilogConstructorTest : Example class used in Naja-verilog unit tests: visit verilog and collect in simple data structures.
  • Unit tests : covers trough unit testing most of the parser aspects.
  • SNLVRLConstructor : More concrete example showing Naja SNL (C++ gate netlist data structure) construction.

The principle of the parser is straightforward: inherit from VerilogConstructor and override callback methods launched while visiting verilog source.

Two passes Parsing

As ordering of verilog modules in single or across multiple files is not preknown and module interfaces need to be created before instances and connectivity are created, parsing can be done in a two pass way with:

  • Parse modules, ports and parameters. Ignore instances and connectivity. Construct all interfaces.
  • Reparse. Ignore ports and parameters. Parse instances and nets. Construct connectivity.

Stuctures (Net, Port, Expression) details constructed by following callbacks can be found in VerilogType.h header.

Callbacks for Module

Starting a module.

This callback is invoked when a module declaration begins. It receives the name of the module as an argument.

For instance, the callback is called with name="foo" for the Verilog module declaration below:

Ending a Module

This function is called upon reaching the end of a module declaration. It serves as a notifier for the end of the module's scope, allowing for any necessary cleanup.

The corresponding verilog end declaration is:

Callbacks for Ports

Simple port declaration in module interface.

Triggered when a module uses a simple declaration (only the port name) for ports. It will be called multiple times depending on the number of ports declared.

For example, it is called with name="a", name="b", and name="c" for:

Port details in module implementation

Associated to previous method, following method collects port details: direction and size in module implementation section.

is called for each port listed in the implementation section of a module.

Port complete declaration in Module interface

Invoked for a complete interface port declaration, detailing port direction (input/output/inout) and in case of bus: msb and lsb.

Callbacks for Nets

This callback is invoked for each net declaration within a module and will construct Net structure containing net details: msb, lsb (for busses) and type: Wire, Supply0 or Supply1.

Assign statements

is called for each assign statement, facilitating the capture of signal assignments.

Below are Verilog examples followed by pseudo C++ representations of the data structures that might be constructed by this callback.

Callback for instances

Starting instantiation.

allows to collect module (used as a model) name for one or multiple instanciations. This method will collect modelName=Model for the two following declarations:

Adding an Instance

will be called 3 times with instanceName=ins1, ins2, ins3 for following declaration:

Ending Instantiation

is called at the conclusion of an instance declaration, it signals that all instances have been processed and allows for post-processing cleanup.

Callbacks for Instance Connections

Named port connection.

This function is called for each named port connection in an instance, capturing the relationship between the port and its connected net or expression.

Ordered Port Connection

is invoked for each port connection when ports are connected by order rather than by name.

Callback for Parameter Assignment

This callback function is designed to handle parameter assignments within module instantiations.

  • Verilog 2.6%

...

Blocking and Non-blocking Assignment in Verilog

  • Assignment is only done in procedural block(always ot initial block)
  • Both combintational and sequential circuit can be described.
  • Assignment can only possible to reg type irrespect of circuit type

Let's say we want to describe a 4-bit shift register in Verilog. For this, we are required to declare a 3-bit reg type variable.

The output of shift[0] is the input of shift[1], output of shift[1] is input of shift[2], and all have the same clock. Let's complete the description using both assignment operator.

Non-Blocking Assignment

When we do synthesis, it consider non-blocking assignment separately for generating a netlist. If we see register assignment in below Verilog code, all register are different if we consider non-blocking assignment separately. If you do the synthesis, it will generate 3 registers with three input/output interconnects with a positive edge clock interconnect for all register. Based on the Verilog description, all are connected sequentially because shift[0] is assigned d, shift[1] is assigned shift[0], and shift[2] is assigned shift[1].

Blocking Assignment

If we use blocking assignment and do the syhtheis, the synthesis tool first generate netlist for first blocking assignment and then go for the next blocking assignment. If in next blocking assignment, if previous output of the register is assigned to next, it will generate only a wire of previously assigned register.

In below Verilog code, even though all looks three different assignment but synthesis tool generate netlist for first blocking assigment which is one register, working on positive edge of clock, input d and output shift[0]. Since blocking assignment is used, for next blocking assignment, only wire is generated which is connected to shift[0]. Same is for next statement a wire is generated which is connected to shift[0].

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verilog netlist assign

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网表中assign语句的产生以及消除方法

verilog netlist assign

转载自 http://blog.sina.com.cn/s/blog_8a5e03d50102vgn1.html

——————————————————————————————————————————————

因为后端布局布线工具,很难读取包含tri wires ,tran 源语,assign语句的网表。因此要求我们在生成网表的时候尽可能消除assign语句。DC综合时在什么情况下会出现assign语句呢。​

1、block的port如果是inout信号,DC产生tri wire 语句和tran 源语。​(网表中包括三态元素),rtl代码中出现一个信号,驱动两个output的port时。

2、当设计中出现同一模块input port和output port直接相连(feedthrough)。​

3、 output port连结到ground或被一常数(1‘b0,0’b0)驱动,DC都会在网表中产生assign语句。​

怎么消除呢?​​

1、第一种情况,通过设置set verilogout_no_tri=true,使DC 将tri_state net宣称为wire。​

2、第二种情况和第三种情况,这样block内的feedthrough问题会被修正,inpu和output之间插buffer去修正。可以通过设置​,

set_fix_mulitple_port_nets -feedthrough

sset_fix_multiple_port_nets -all -buffer_constants​​

3、如果以上处理都不能解决问题。则设计中可能存在具有dont_touch属性的net,可用如下命令将net的dont_touch移去。

remove_attribute find(net,) dont_touch​

define_name_rules MY_RULES -equal_ports_nets

change_name -hier -rules MY_RULES -verbose​

问题:​ I have a feedthrough in my circuit, and the netlist is showing an assign statement for this feedthrough.

我的电路设计中有端口直接连接,综合后网表中使用assign语句用于此连接。

How can I remove the assign statement from the netlist?;

我如何去除网表中的assign语句?

回答: The two most common reasons for assign statements to appear in a gate-level netlist are

两个最可能的原因会造成在门级网表中出现assign语句:

(1) there are feedthroughs that connect multiple ports on a single net or

一条网络上连接多个端口,或者

(2) the netlist contains three-state elements

Feedthrough

Nets直接连接网络​

HDL Compiler creates assign statements in the design when two ports are connected without logicbetween them. If a feedthrough has an output port connected to an input port without any logic inbetween, it causes Design Compiler to add the assign statement in the netlist. Design Compiler isunable to represent such connections without using nonstructural artifacts such as the assignstatement.

当设计中两个端口之间没有逻辑直接相连时,HDL编译器会用assign语句。如果从输入端口到输出端口的连接中间没有逻辑,DC编译器会在网表中加入assign语句。不用assign语句,DC将不会表达这种连接。

To fix this problem, you need to add logic to the design to correctly represent the otherwiseunrepresentable connections. To fix the feedthrough in the design, use this command before compile:

要修复此问题,你需要增加逻辑正确表达这种连接。要修复设计中端口直接连接,在编译前使用如下命令:

set_fix_multiple_port_nets -all -buffer_constants​

Design Compiler will then insert logic into the design to prevent ports from being connected to thesame net.

DC编译器会插入逻辑以避免设计中多个端口连接到同一个网络。

If the net has a dont_touch attribute on it, Design Compiler is not allowed to insert logic between theinput and output port connections, and the assign statement will remain in your netlist.

如果此网络具有dont_touch属性,DC编译器将不被允许在输入输出端口连接中间插入逻辑,assign语句还会存在于网表中。

You can correct this situation in the following ways:

你可以使用下面方法修复:

1. Remove the dont_touch attribute.  去除dont_touch属性

2. Manually insert a buffer on the net between the input and output ports to prevent the assignstatement. 

 在输入端口和输出端口间手动插入一个buffer来避免assign语句。

Three-State Elements三态元素​

To avoid getting assign statements with three-state elements, set the verilogout_no_tri variable totrue before writing out the netlist. Also, check that verilogout_equation is set to false.

要避免有三态元素引起的assign语句,在写出网表文件之前,设定verilogout_no_tri变量为true,且检查变量verilogout_equation设定为false。

v ​ erilogout_no_tri = true

verilogout_equation = false​

You can read in your compiled .db file, set the verilogout variables, and then write out the netlist.(The verilogout_equation and verilogout_no_tri variables determine the Verilog output with thewrite -f verilog -hier -o command.) The verilogout_equation and verilogout_no_tri variables do notaffect the compile process.

你可以读入你的编译后的.db文件,设定verilogout变量,然后写出网表文件。(变量verilogout_no_tri和verilogout_equation与命令write -f verilog -hier -o一起决定了verilog的输出。)变量verilogout_no_tri和verilogout_equation不影响编译过程。

To see whether the settings help eliminate the assign statements, set the variables and thenwrite the netlist. Here is a small example of the steps required to do this in dcsh mode:​​​​​

要看这些设定是否帮助消除了assign语句,可以设定这些变量然后写出网表。这里提供一个dcsh格式的例子。

verilogout_equation = false

verilogout_no_tri = true

read -f db your_compiled_file.db

list   verilogout_equation

list verilogout_no_tri

write -f verilog -hierarchy -o netlist.v

write -f db -hierarchy -o netlist.db

2010年12月6日补充:

当使用上述方法去除assign后,写出的网表文件中还是包含assign语句。使用report_comile_options命令来报告每一个design的编译选项,发现只有top的具有fix_multiple_port_nets选项。而我编译时没有使用ungroup_all选项,分析应该是编译时只是对顶层design去除了assign语句,而其它层次的design中依然保留有assign语句。

解决办法:编译时使用-ungroup_all选项

compile -ungroup_all

2010年12月17日补充:

12月6日的补充有问题。用report_compile_options命令只会显示top设计有没有fix_multiple_port_nets选项。如果有此选项,表示其整个设计的hierarchy都会在编译时fix_multiple_port_nets。所以,assign出现的原因并不是有些sub-level design没有fix_multiple_port_nets属性造成的。我也查找排除了dont_touch属性而导致编译器不能去除assign语句。

发现使用change_names -hier -rules verilog可以去除assign语句。分析应该是verilog命名规则中两个选项起的作用:

equal_ports_nets: true

inout_ports_equal_nets: true

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  1. Verilog netlist synthesis using assign vs always

    Verilog netlist synthesis using assign vs always - Electrical Engineering Stack Exchange Verilog netlist synthesis using assign vs always [duplicate] Ask Question Asked 11 months ago Modified 11 months ago Viewed 127 times 2 This question already has an answer here : always @ (*) vs. assign (1 answer) Closed 12 months ago.

  2. PDF Netlist Design Flow

    • Verilog History • Introduction to Verilog • Verilog Basics Spring 2005 EECS150 - Lec04-Verilo g1 Page 3 Netlist • A key data structure (or representation) in the design process is the "netlist": - Network List • A netlist lists components and connects them with nodes: ex: g1 "and" n1 n2 n5 g2 "and" n3 n4 n6 g3 "or" n5 n6 n7

  3. Netlist with "assign" / RC and Encounter

    EDI saveNetlist gives a Verilog netlist with assign statement When running saveNetlist in EDI, I got a hierarchical Verilog netlist with assign statement in use! Some nets have the names that are different in the netlist from what I see in the GUI after layout....

  4. EDI saveNetlist gives a Verilog netlist with assign statement

    Votes Oldest Newest xfan over 9 years ago By the way, we are now using EDI version 14.10. When running saveNetlist in EDI, I got a hierarchical Verilog netlist with assign statement in use! Some nets have the names that are different in the netlist from

  5. PDF Intro to Verilog

    Microsoft PowerPoint - L03_Verilog v2.pptx. Intro to Verilog. • Wires - theory vs reality (Lab1) • Hardware Description Languages. • Verilog -- structural: modules, instances -- dataflow: continuous assignment -- sequential behavior: always blocks -- pitfalls -- other useful features. Reminder: Lab #1 due by 9pm tonight.

  6. Netlists

    Overview The netlist logically consists of several different components: Blocks, Ports, Pins and Nets Each component in the netlist has a unique template identifier (BlockId, PortId, PinId, NetId) used to retrieve information about it.

  7. Netlist Format

    Netlist Format — Icarus Verilog documentation Netlist Format ¶ The output from the parse and elaboration steps is a "netlist" rooted in a Design object. Parsing translates the design described in the initial source file into a temporary symbolic "pform".

  8. How to edit and test a verilog netlist

    system-verilog netlist Share Improve this question Follow edited May 11, 2020 at 8:40 asked Mar 25, 2020 at 11:45 Pragash B 21 3 The output is verilog. You could simply compile it in Modelsim, just like you would with behavioral-style Verilog RTL that you'd have synthesized to create this netlist. - Arun D'souza Mar 25, 2020 at 15:00 1

  9. PDF vlang: Mapping Verilog Netlists to Modern Technologies

    We present vlang, a LLVM-frontend to compile a Verilog netlist into LLVM's IR. vlang's compilation process for a Verilog netlist is outlined in Fig. 1. In this process, a Verilog netlist is first parsed into a software model. The software-model holds information regarding the primitives (e.g., LUTs, AND-Gates, Flip-Flops, etc.) in the supplied

  10. why after synthesis have assign?

    #1 S stormwolf Advanced Member level 4 Joined Jan 3, 2004 Messages 112 Helped 12 Reputation 24 Reaction score 0 Trophy points 1,296 Activity points 777 synthesis assign After i synthesis a chip, and generate a netlist. I read the netlist find at netlist have "assign" command . Don't the "assign" effect backend tools such as astro? Feb 1, 2005 #2 S

  11. PDF Creating a verilog netlist for a schematic

    The "verilog.inpfiles" window appears as shown in Fig 9. It shows you which cds directory has the netlist for which schematic. Save all the netlists in the silicon ensemble directory with a .v extension. b. Run the Verilog correction (verilog_correction) script on the netlist of the top cell. This file is run by the following command.

  12. Verilog::Netlist::ContAssign

    DESCRIPTION A Verilog::Netlist::ContAssign object is created by Verilog::Netlist for every continuous assignment statement in the current module. ACCESSORS See also Verilog::Netlist::Subclass for additional accessors and methods. $self->keyword Keyword used to declare the assignment. Currently "assign" is the only supported value. $self->lhs

  13. GitHub

    Gate level netlist. This parser is dedicated to a very small part of verilog: the subset allowing to describe hierarchical gate level netlists. This is the format found at the output of synthesis tools such as Yosys. To parse complete RTL level verilog or system verilog, please use projects such as: Verible. Apart the language support, the main ...

  14. Blocking and Non-blocking Assignment in Verilog

    When we do synthesis, it consider non-blocking assignment separately for generating a netlist. If we see register assignment in below Verilog code, all register are different if we consider non-blocking assignment separately. If you do the synthesis, it will generate 3 registers with three input/output interconnects with a positive edge clock ...

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    assign output = x ^ y ASIC or FPGA toolchains translate Verilog to a gate-level netlist Verilog Modules Modules are the building blocks of Verilog designs. They are a means of abstraction and encapsulation for your design. A module consists of a port declaration and Verilog code to implement the desired functionality.

  16. Avoiding Asssign Statement in Verilog Netlist

    Assign statements are undesired in Verilog netlists. SetDoAssign removes assign statements from a netlist. But in some cases the resulting netlist will have problems.

  17. 网表中assign语句的产生以及消除方法

    1、第一种情况,通过设置set verilogout_no_tri=true,使DC 将tri_state net宣称为wire。 2、第二种情况和第三种情况,这样block内的feedthrough问题会被修正,inpu和output之间插buffer去修正。 可以通过设置 , set_fix_mulitple_port_nets -feedthrough sset_fix_multiple_port_nets -all -buffer_constants 3、如果以上处理都不能解决问题。 则设计中可能存在具有dont_touch属性的net,可用如下命令将net的dont_touch移去。 remove_attribute find (net,) dont_touch