Verilog assign statement

Hardware schematic.

Signals of type wire or a similar wire like data type requires the continuous assignment of a value. For example, consider an electrical wire used to connect pieces on a breadboard. As long as the +5V battery is applied to one end of the wire, the component connected to the other end of the wire will get the required voltage.

breadboard-circuit

In Verilog, this concept is realized by the assign statement where any wire or other similar wire like data-types can be driven continuously with a value. The value can either be a constant or an expression comprising of a group of signals.

Assign Syntax

The assignment syntax starts with the keyword assign followed by the signal name which can be either a single signal or a concatenation of different signal nets. The drive strength and delay are optional and are mostly used for dataflow modeling than synthesizing into real hardware. The expression or signal on the right hand side is evaluated and assigned to the net or expression of nets on the left hand side.

Delay values are useful for specifying delays for gates and are used to model timing behavior in real hardware because the value dictates when the net should be assigned with the evaluated value.

  • LHS should always be a scalar or vector net or a concatenation of scalar or vector nets and never a scalar or vector register.
  • RHS can contain scalar or vector registers and function calls.
  • Whenever any operand on the RHS changes in value, LHS will be updated with the new value.
  • assign statements are also called continuous assignments and are always active

In the following example, a net called out is driven continuously by an expression of signals. i1 and i2 with the logical AND & form the expression.

assign-flash-1

If the wires are instead converted into ports and synthesized, we will get an RTL schematic like the one shown below after synthesis.

verilog assignment pattern

Continuous assignment statement can be used to represent combinational gates in Verilog.

The module shown below takes two inputs and uses an assign statement to drive the output z using part-select and multiple bit concatenations. Treat each case as the only code in the module, else many assign statements on the same signal will definitely make the output become X.

Assign reg variables

It is illegal to drive or assign reg type variables with an assign statement. This is because a reg variable is capable of storing data and does not require to be driven continuously. reg signals can only be driven in procedural blocks like initial and always .

Implicit Continuous Assignment

When an assign statement is used to assign the given net with some value, it is called explicit assignment. Verilog also allows an assignment to be done when the net is declared and is called implicit assignment.

Combinational Logic Design

Consider the following digital circuit made from combinational gates and the corresponding Verilog code.

combinational-gates

Combinational logic requires the inputs to be continuously driven to maintain the output unlike sequential elements like flip flops where the value is captured and stored at the edge of a clock. So an assign statement fits the purpose the well because the output o is updated whenever any of the inputs on the right hand side change.

After design elaboration and synthesis, we do get to see a combinational circuit that would behave the same way as modeled by the assign statement.

combinational gate schematic

See that the signal o becomes 1 whenever the combinational expression on the RHS becomes true. Similarly o becomes 0 when RHS is false. Output o is X from 0ns to 10ns because inputs are X during the same time.

combo-gates-wave

Click here for a slideshow with simulation example !

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Mastering Format Specifications in Verilog and SystemVerilog: A Comprehensive Guide

In the digital design and coding world, Verilog and SystemVerilog stand as two of the most reliable and widely used hardware description languages. A pivotal feature of these languages, enhancing the debugging process and code comprehension, is the employment of format specifications. Format specifications regulate how data appears when utilizing I/O system tasks.

Here's a brief overview of the format specifications we'll discuss:

In this comprehensive guide, we'll explore these specifications to help you decipher the code and output in Verilog and SystemVerilog. Let's embark on this informative journey!

%d, %o, %h, %x, %b - Exploring Decimal, Octal, Hexadecimal, and Binary Formats

In Verilog and SystemVerilog programming, you'll frequently utilize the $display function to present data in your preferred format. Specific format specifiers, like %d for decimal, %o for octal, %h or %x for hexadecimal, and %b for binary, help shape your data's appearance.

Consider an example where we display a 12-bit register value in these various formats:

The output would present the twelveBitReg value in each of the specified formats. Notably, we've utilized %4d and %3h or %3x to control the output width—a potent feature when handling varied-sized data, enhancing your output's clarity and readability.

%c, %s - Decoding ASCII Character and String Formats

Verilog and SystemVerilog allow us to interpret ASCII codes as characters and to display strings—convenient for printing messages or data in human-readable format:

The %c format specifier displays the ASCII character equivalent of a byte, and %s is used to display strings.

%e, %f, %g - Mastering the Art of Displaying Real Numbers

Real numbers in SystemVerilog can be displayed in exponential, decimal, or a shorter version of both. This feature proves incredibly useful when handling large floating-point numbers or precision decimal numbers:

Here, %e displays in exponential format, %f in decimal format, and %g selects the shorter of the two.

%l, %m - Deciphering Library Binding and Hierarchical Names in SystemVerilog

In SystemVerilog, %l and %m formatting specifiers perform unique roles. The %l specifier outputs the library details of a module instance in a "library.cell" format, illuminating the origin library and the cell name of the current instance. Similarly, the %m specifier displays the hierarchical name of the invoking design element, whether it's a subroutine, a named block, or any other labeled statement. This is particularly handy when dealing with multiple instances of a module and needing to trace a specific system task's source.

Let's witness both specifiers in action within a single module:

The brilliance of both %l and %m is that they don't require arguments—they directly refer to the library and hierarchical name details of the current instance, respectively. These specifiers are a debugging boon, aiding in more efficient issue identification and resolution.

%v - Unveiling Net Signal Strength in SystemVerilog

Signal strength in SystemVerilog is crucial for evaluating a net's driving capability. To determine this, we use the %v format specifier. It presents the strength of scalar nets in a three-character format: the first two characters represent the strength, while the third signifies the scalar's logic value.

Here's an illustration of how it works:

In this module, %v reveals the strength of weakPullUpWire .

The strength levels are either represented by a mnemonic or a pair of decimal digits, indicating a range of strength levels. Below is a brief overview of strength mnemonics and their corresponding strength levels:

The third character, representing the scalar's logic value, can be:

Using the %v format specifier, you can gain deeper insights into your scalar nets' signal strength, making debugging and performance optimizations more streamlined.

%p - Deciphering Assignment Patterns in SystemVerilog

SystemVerilog's %p format specifier offers a versatile tool for displaying complex data structures. The following example demonstrates how to represent an unpacked structure in an assignment pattern:

The %p specifier neatly presents the abStruct value. Here are some highlights of its usage:

  • Structures are represented with named elements.
  • Enum types display as their name, if valid.
  • String types appear in quotes.
  • Unique types like class handles show in a distinct format, with null values as 'null'.
  • Other types are printed unformatted.

For a condensed view of aggregate expressions, the %0p format specifier is used. It's a more compact, implementation-dependent alternative.

In essence, the %p and %0p format specifiers provide a neat way of interpreting complex data structures in SystemVerilog.

%t - Understanding Current Time Format

Last but not least, %t is used to display the current simulation time. This can be very useful for tracking event timing during simulation:

This will display the current simulation time (5 time units) when it is called.

%u, %z - Handling Unformatted Binary Data

SystemVerilog has distinct specifications for writing unformatted binary data: %u (or %U ) and %z (or %Z ). These specifications work best with $fwrite when transmitting data to external programs.

The %u specifier writes binary data to the output, disregarding any unknown or high-impedance bits by treating them as zero. This is useful for transferring data to external applications that only recognize binary data.

Conversely, the %z specifier supports the transfer of binary data while preserving unknown ( x ) and high-impedance ( z ) bits. It's designed for communication with programs that understand and accommodate these bits.

Here's a unified example:

Both specifiers write data in the native endian format of the system, in 32-bit units, with the word containing the LSB written first. Note that for POSIX applications, files should be opened with wb , wb+ , or w+b specifiers to prevent the system from altering patterns in the unformatted stream that resemble special characters.

Whether you're a seasoned veteran or a newcomer to Verilog and SystemVerilog, understanding and using format specifications can significantly enhance your coding and debugging process. They allow for clear, concise, and context-specific displays of data, making your output more readable and your code easier to debug.

verilog assignment pattern

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Verilog Empty Assignment Pattern

A SystemVerilog queue or dynamic array can be initialized by using an empty assignment pattern. Though other constructs, such as structs and associative arrays, cannot be initialized this way.

Using Continuous Assignment to Model Combinational Logic in Verilog

In this post, we talk about continuous assignment in verilog using the assign keyword. We then look at how we can model basic logic gates and multiplexors in verilog using continuous assignment.

There are two main classes of digital circuit which we can model in verilog – combinational and sequential .

Combinational logic is the simplest of the two, consisting solely of basic logic gates, such as ANDs, ORs and NOTs. When the circuit input changes, the output changes almost immediately (there is a small delay as signals propagate through the circuit).

In contrast, sequential circuits use a clock and require storage elements such as flip flops . As a result, output changes are synchronized to the circuit clock and are not immediate.

In this post, we talk about the techniques we can use to design combinational logic circuits in verilog. In the next post, we will discuss the techniques we use to model basic sequential circuits .

Continuous Assignment in Verilog

We use continuous assignment to drive data onto verilog net types in our designs. As a result of this, we often use continuous assignment to model combinational logic circuits.

We can actually use two different methods to implement continuous assignment in verilog.

The first of these is known as explicit continuous assignment. This is the most commonly used method for continuous assignment in verilog.

In addition, we can also use implicit continuous assignment, or net declaration assignment as it is also known. This method is less common but it can allow us to write less code.

Let's look at both of these techniques in more detail.

  • Explicit Continuous Assignment

We normally use the assign keyword when we want to use continuous assignment in verilog. This approach is known as explicit continuous assignment.

The verilog code below shows the general syntax for continuous assignment using the assign keyword.

The <variable> field in the code above is the name of the signal which we are assigning data to. We can only use continuous assignment to assign data to net type variables.

The <value> field can be a fixed value or we can create an expression using the verilog operators we discussed in a previous post. We can use either variable or net types in this expression.

When we use continuous assignment, the <variable> value changes whenever one of the signals in the <value> field changes state.

The code snippet below shows the most basic example of continuous assignment in verilog. In this case, whenever the b signal changes states, the value of a is updated so that it is equal to b.

  • Net Declaration Assignment

We can also use implicit continuous assignment in our verilog designs. This approach is also commonly known as net declaration assignment in verilog.

When we use net declaration assignment, we place a continuous assignment in the statement which declares our signal. This can allow us to reduce the amount of code we have to write.

To use net declaration assignment in verilog, we use the = symbol to assign a value to a signal when we declare it.

The code snippet below shows the general syntax we use for net declaration assignment.

The variable and value fields have the same function for both explicit continuous assignment and net declaration assignment.

As an example, the verilog code below shows how we would use net declaration assignment to assign the value of b to signal a.

Modelling Combinational Logic Circuits in Verilog

We use continuous assignment and the verilog operators to model basic combinational logic circuits in verilog.

To show we would do this, let's look at the very basic example of a three input and gate as shown below.

To model this circuit in verilog, we use the assign keyword to drive the data on to the and_out output. This means that the and_out signal must be declared as a net type variable, such as a wire.

We can then use the bit wise and operator (&) to model the behavior of the and gate.

The code snippet below shows how we would model this three input and gate in verilog.

This example shows how simple it is to design basic combinational logic circuits in verilog. If we need to change the functionality of the logic gate, we can simply use a different verilog bit wise operator .

If we need to build a more complex combinational logic circuit, it is also possible for us to use a mixture of different bit wise operators.

To demonstrate this, let's consider the basic circuit shown below as an example.

To model this circuit in verilog, we need to use a mixture of the bit wise and (&) and or (|) operators. The code snippet below shows how we would implement this circuit in verilog.

Again, this code is relatively straight forward to understand as it makes use of the verilog bit wise operators which we discussed in the last post.

However, we need to make sure that we use brackets to model more complex logic circuit. Not only does this ensure that the circuit operates properly, it also makes our code easier to read and maintain.

Modelling Multiplexors in Verilog

Multiplexors are another component which are commonly used in combinational logic circuits.

In verilog, there are a number of ways we can model these components.

One of these methods uses a construct known as an always block . We normally use this construct to model sequential logic circuits, which is the topic of the next post in this series. Therefore, we will look at this approach in more detail the next blog post.

In the rest of this post, we will look at the other methods we can use to model multiplexors.

  • Verilog Conditional Operator

As we talked about in a previous blog, there is a conditional operator in verilog . This functions in the same way as the conditional operator in the C programming language.

To use the conditional operator, we write a logical expression before the ? operator which is then evaluated to see if it is true or false.

The output is assigned to one of two values depending on whether the expression is true or false.

The verilog code below shows the general syntax which the conditional operator uses.

From this example, it is clear how we can create a basic two to one multiplexor using this operator.

However, let's look at the example of a simple 2 to 1 multiplexor as shown in the circuit diagram below.

The code snippet below shows how we would use the conditional operator to model this multiplexor in verilog.

  • Nested Conditional Operators

Although this is not common, we can also write code to build larger multiplexors by nesting conditional operators.

To show how this is done, let's consider a basic 4 to 1 multiplexor as shown in the circuit below.

To model this in verilog using the conditional operator, we treat the multiplexor circuit as if it were a pair of two input multiplexors.

This means one multiplexor will select between inputs A and B whilst the other selects between C and D. Both of these multiplexors use the LSB of the address signal as the address pin.

To create the full four input multiplexor, we would then need another multiplexor.

This takes the outputs from the first two multiplexors and uses the MSB of the address signal to select between them.

The code snippet below shows the simplest way to do this. This code uses the signals mux1 and mux2 which we defined in the last example.

However, we could easily remove the mux1 and mux2 signals from this code and instead use nested conditional operators.

This reduces the amount of code that we would have to write without affecting the functionality.

The code snippet below shows how we would do this.

As we can see from this example, when we use conditional operators to model multiplexors in verilog, the code can quickly become difficult to understand. Therefore, we should only use this method to model small multiplexors.

  • Arrays as Multiplexors

It is also possible for us to use verilog arrays to build simple multiplexors.

To do this we combine all of the multiplexor inputs into a single array type and use the address to point at an element in the array.

To get a better idea of how this works in practise, let's consider a basic four to one multiplexor as an example.

The first thing we must do is combine our input signals into an array. There are two ways in which we can do this.

Firstly, we can declare an array and then assign all of the individual bits, as shown in the verilog code below.

Alternatively we can use the verilog concatenation operator , which allows us to assign the entire array in one line of code.

To do this, we use a pair of curly braces - { } - and list the elements we wish to include in the array inside of them.

When we use the concatenation operator we can also declare and assign the variable in one statement, as long as we use a net type.

The verilog code below shows how we can use the concatenation operator to populate an array.

As verilog is a loosely typed language , we can use the two bit addr signal as if it were an integer type. This signal then acts as a pointer that determines which of the four elements to select.

The code snippet below demonstrates this method in practise. As the mux output is a wire, we must use continuous assignment in this instance.

What is the difference between implicit and explicit continuous assignment?

When we use implicit continuous assignment we assign the variable a value when we declare. When we use explicit continuous assignment we use the assign keyword to assign a value.

Write the code for a 2 to 1 multiplexor using any of the methods discussed we discussed.

Write the code for circuit below using both implicit and explicit continuous assignment.

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  • Verilog Assignments

09 Sep 2021

In Verilog, there are various ways for assignment, due to the concurrent nature of the Verilog code. Also, to represent the combinational and sequential digital circuits, Verilog provides different ways for assignment which helps to model the hardware accurately.

As we know, Verilog has net and reg data types, which represent a wire and flip flop respectively. From hardware point of view, wires are driven continuously once the circuit is switched on, thus for every point of time wire will take the value which is fed into as it cannot retain any previous value. To represent this behaviour, Verilog provides continuous assignment. This will assign certain value to the wire at every time step.

Similarly, flip flops, are not driven continuously, rather it is driven at some clock edge or any other event, as flip flops retain the value until it is changed. This is the expected behaviour in sequential circuits. To represent this behaviour, Verilog provides procedural assignment, in which the assignment will be done only if certain event is triggered. Let’s see these assignments in detail.

Continuous Assignment

As discussed earlier this assignment is generally used for net data types. assign keyword is used for continuous assignment and is used directly inside the module, i.e., procedural blocks are not required for this type of assignment.

Procedural Assignment

Procedural assignments are used with flip flops, i.e., for sequential circuits. Thus, it can be used to drive only variables and not any net data type. Also, this type of assignment can only be used inside a procedural block, i.e., initial or always .

Procedural assignment can further be divided into 2 types:

Blocking Assignment

  • Non-blocking Assignments

This type of assignment is the same as we see in all the programming language. As the name suggests, program flow will be blocked until the assignment is complete. This assignment is done using the help of = operator, which is also known as blocking assignment operator. Blocking assignment is executed in the Active region of the event semantics . As we know, the active region does not guarantee the order of execution, thus this type of assignment is prone to race conditions as discussed in previous article.

Non-blocking Assignment

This type of assignment, as name suggests, does not block the flow of program. The RHS of the assignment operation is calculated but it is not assigned to LHS. All the non-blocking assignments are executed at the end of the time-step in NBA region of event semantics and the LHS gets assigned with the calculated RHS. NBAs are done using <= operator which is also known as non-blocking assignment operator. As this assignment is done in NBA region, it helps prevent race around condition. We will see how this prevents race around condition with example later in this article.

Procedural Continuous Assignment

This is a continuous assignment which is used inside the procedural blocks. This is mainly used when we want to override the value of a variable or net. These types of assignments can be achieved using

  • assign - deassign keyword
  • force - release keyword.

Assign deassign keywords

These are used to override the value of a variable until the variable is de-assigned using deassign keyword. After de-assignment, the value of the variable will remain the same until it is re-assigned using procedural or procedural continuous assignment. These can be used only used when LHS is a variable or concatenation of variable.

In below example, the value of a is continuously incremented in the first initial block. In the second initial block, at t=17 , the value of a is overridden using assign keyword, and thus the value of a is not getting incremented. Once deassign is used at t=27 , the value of a starts getting incremented.

The value of a is not getting printed once the value of a is overridden, as $monitor prints only when the value of the variable changes. As assign does not let the value change, thus value of a is not getting printed even after a is incremented.

Force release keyword

These are same as that of assign-deassign statement but it can be used for both nets and variables. The LHS can be a bit-select, part-select of net but cannot be an array or a bit or part select of variables. These will override all other assignments until released.

In below example, b is continuously assigned ~a , i.e., inverse of a. In first initial block value of a is incremented and the value of b also changes. In second initial block, at t=15 value of a is overridden using force keyword. Value of b changes with response to a . At t=25 value of b[2:1] is overridden with force keyword, and thus now only the first and last bit of b can change. At t=35 variable a is released, and value of a can be changed, but net b is still not released, so only the first and the last bit of b changes with change in a . At t=45 net b is also released and now all bits of b is changed with change in a .

Prevention of race around condition

Race around condition, which was discussed in earlier article , can be prevented by using a non-blocking assignment. As we know in non-blocking assignment, the LHS is assigned in the non-blocking region of event semantics, which comes after the active regions, thus the value is determinate as all the calculations have been already done. Let’s understand this with an example.

In the 1st code, at the positive edge of clk , variable a is assigned a value whereas at the same time b is reading of value of a . As order of execution in active region is not guaranteed in Verilog, thus it can lead to a race around condition.

Whereas in 2nd code, as non-blocking assignment is used, thus 1 will not be assigned immediately to a . Now when, b access the variable a it will always read the previous value stored, in this case 0 . Thus, b will be assigned with 0 and a will be assigned with 1 at the send of the time step. Also note that for b to attain the value of a , it takes 2 cycles, thus at t=30, b = 1

1st code - having race around condition

2nd code - solution for race condition.

  • Introduction to Verilog
  • Verilog Event Semantics
  • Basics of Verilog
  • Verilog Syntax
  • Data Types in Verilog
  • Verilog Vectors
  • Verilog Arrays
  • Verilog Modules
  • Verilog Ports
  • Verilog Operators
  • Verilog Procedural Blocks
  • Different types of loops in Verilog
  • Conditional Statements in Verilog
  • Verilog functions and tasks
  • Compiler Directives in Verilog
  • Verilog System Functions
  • Delays in Verilog
  • The Verilog-AMS Language
  • Analog Processes
  • Assignment Statements

Assignment Statements 

Contribution .

A contribution statement is used to give values to continuous signals, in particular to branch potentials or flows:

This statement says that the voltage on the branch named ‘res’ should be driven so that the voltage on the branch should equal r multiplied by the current through the branch.

Contributions may be either explicit, as above, or implicit. Implicit contributions have the target on both sides of the contribution operator. For example:

This implements the series combination of a resistor and a capacitor.

Implicit contributions to branch flows can be used to easily create series combinations whereas implicit contributions to branch potentials can be used to create parallel combinations. For example, the following creates the parallel combination of an inductor and a conductor:

Multiple contributions to the same branch in the same analog process accumulate. For example:

This is equivalent to:

Multiple contributions to a branch flow can be viewed as creating multiple parallel branches. For example, the above example is equivalent to the parallel combination of the output of a controlled current source, a conductor, and a capacitor. Similarly, multiple contributions to a branch potential can be viewed as creating multiple series branches.

The target (left side) must be a branch signal: an access function applied to a continuous branch. The branch may be a named (or explicit) branch, or it may be an unnamed (or implicit) branch, which are given as a single net or a pair of nets. When an implicit branch is given as a pair of nets, the branch is assumed to connect the two nets. When an implicit branch is specified as a single net, the branch is assumed to connect that net to ground.

Here is a resistor module that uses a explicitly declared or named branch:

Here is a resistor module that uses a implicitly declared or unnamed branch:

Descriptions that employ unnamed branches are a little more compact, but also the formulation of the branches is constrained (multiple contributions to flows give a shunt toplogy and to potentials gives a series topology). For this reason people use unnamed branches with the branch topology is simple, and switch to named branches for the more complicated topologies.

The actual contributions occur after the analog block has been evaluated, meaning that the branch values do not change between statements in the analog block. As such, so as long as the values of the right-hand side expressions are not affected, the order of the contribution statements is inconsequential. So for example, these two analog blocks are equivalent:

Indirect Assignment 

An indirect assignment is an alternative to the contribution statement. It also drives a particular branch potential or flow so that a given equation is satisfied, but in this case the driven branch potential or flow need not be in the specified equation. This feature is rarely needed, however it occasionally allows you to describe a component that would cumbersome to describe with contributions. For example, it is possible to describe an ideal opamp using:

This can be read as ‘drive V(out) such that V(pin,nin) == 0’.

The left side of the equation must be either a branch potential or flow, the right side is an expression. The equation may be implicit or explicit.

The driven branch must not also be a target of a contribution statement.

Assignment 

A assignment evaluates the expression on its right hand side and then immediately assigns the value to the variable on its left hand side:

The target (left side) of an analog assignment statement may only be a integer or real variable. It may not be signal or a wire.

Contribution versus Assignment 

For people new to Verilog-A and Verilog-AMS, contribution and assignment seem to be doing very similar things, and this can confuse them. Here the differences between contribution and assignment are highlighted.

verilog assignment pattern

Gabbed (Member) asked a question.

Hi, i was trying to implement a floating point (single precision) adder. Vivado tells me that there is an error: [Synth 8-359] invalid assignment pattern basically where there is: EffectiveMantissa_A = {1'b1, A.Mantissa};). Can someone help me? (I even tried with the '{ } operand)

package FloP_32; typedef struct packed { logic Sign; //Segno logic [7:0] Exponent; //Esponente logic [22:0] Mantissa; //Mantissa } FloP_Number; endpackage . . . module Shift import FloP_32::FloP_Number; ( input FloP_Number A, B, //Input output FloP_Number A1, B1 //Output );

logic [23:0] EffectiveMantissa_A, EffectiveMantissa_B; //Mantissa effetiva ottenuta inserendo un 1 logic signed [7:0] ExponentComparison; //Confronto esponenti

always_comb begin EffectiveMantissa_A = {1'b1, A.Mantissa}; //Aggiungere l'1 più significativo EffectiveMantissa_B = {1'b1, B.Mantissa}; . . .

verilog assignment pattern

varunra (Member)

I don't see any issue with the code. I tried the same code Vivado didn't see any error. 

Can you share the following

1. which version of vivado are you using? I tried with 2019.2

2. can you share the code, so that we can debug what exactly is causing the error message?

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COMMENTS

  1. Verilog Assignment Patterns

    Verilog Assignment Patterns Sigasi Studio has several checks on Verilog assignment patterns. Default member must be last Concrete assignments must precede more general assignments. Otherwise, some of those assignments might be ignored (rule 28). In particular: for arrays, default must be at the end of the list

  2. Verilog Assignments

    An assignment has two parts - right-hand side (RHS) and left-hand side (LHS) with an equal symbol (=) or a less than-equal symbol (<=) in between. The RHS can contain any expression that evaluates to a final value while the LHS indicates a net or a variable to which the value in RHS is being assigned.

  3. verilog

    In SystemVerilog, it has array assignment pattern and struct assignment pattern syntax. No matter the union construct here is packed or unpacked, whether it is synthesizable or not, is it a valid usage for assignment pattern? If yes, what value should be for union x?

  4. Usage of tick ( ' ) in array assignments -> packed vs unpacked

    assignment patterns require each operands to be assignment compatible with each array element, and there needs to be an operand in the pattern for each element of the array. replication of operands is allowed

  5. Verilog assign statement

    In Verilog, this concept is realized by the assign statement where any wire or other similar wire like data-types can be driven continuously with a value. The value can either be a constant or an expression comprising of a group of signals. Assign Syntax

  6. Apostrophe in Verilog array assignment

    1 Answer Sorted by: 7 SystemVerilog has the array assignment operator ' {...} in addition to the concatenation operator {...}. Concatentation is for packed arrays - basically you combine multiple signals into a single bus. wire [7:0] a = {4'd7, 4'd14}; You can nest concatenation operators too.

  7. Mastering Format Specifications in Verilog and SystemVerilog: A

    Using the %v format specifier, you can gain deeper insights into your scalar nets' signal strength, making debugging and performance optimizations more streamlined. %p - Deciphering Assignment Patterns in SystemVerilog. SystemVerilog's %p format specifier offers a versatile tool for displaying complex data structures. The following example demonstrates how to represent an unpacked structure in ...

  8. Verilog Empty Assignment Pattern

    Verilog Empty Assignment Pattern A SystemVerilog queue or dynamic array can be initialized by using an empty assignment pattern. Though other constructs, such as structs and associative arrays, cannot be initialized this way.

  9. Using Continuous Assignment to Model Combinational Logic in Verilog

    This approach is known as explicit continuous assignment. The verilog code below shows the general syntax for continuous assignment using the assign keyword. assign <variable> = <value>; The <variable> field in the code above is the name of the signal which we are assigning data to. We can only use continuous assignment to assign data to net ...

  10. system verilog

    1 Answer Sorted by: 0 Since these are all packed types, they should all be assignment compatible. I get a syntax error in your typedef - missing a semicolon after s2 ** Error: (vlog-13069) myfile.sv (3): near "}": syntax error, unexpected '}', expecting ';' or ','. Once I fix that, it works for me.

  11. Verilog Assignments

    Verilog Assignments. 09 Sep 2021. 6 mins. In Verilog, there are various ways for assignment, due to the concurrent nature of the Verilog code. Also, to represent the combinational and sequential digital circuits, Verilog provides different ways for assignment which helps to model the hardware accurately. As we know, Verilog has net and reg data ...

  12. Illegal assignment pattern. the number of elements (1) does not match

    1 This is syntactically incorrect. As you are trying to assign a 2-D array to 1-D packed array. According to LRM either right-hand side should be 2-d like this. arr [1:0] [1:0]; assign arr = ' {' {default:1}, ' {default:0} } or it should be assign arr = ' {default:1} Share Improve this answer Follow answered May 16, 2020 at 10:59

  13. SystemVerilog invalid assignment pattern

    SystemVerilog invalid assignment pattern I am working with a complex design using abstract data types and it is going well, for the most part. I am using valid SV code for pattern assignment is resulting in an error with Vivado 2017.4.

  14. Assignment Statements

    Assignment. A assignment evaluates the expression on its right hand side and then immediately assigns the value to the variable on its left hand side: a = b + c; The target (left side) of an analog assignment statement may only be a integer or real variable. It may not be signal or a wire.

  15. system verilog

    1 Here is a snippet from my code; always_ff @ (posedge clk) begin : output_assigment // left side should only be "_q" if (reset_n == 1'b0 || clear == 1'b1) out_signal_q <= {8' {! (REPORT_POL)}}; But i see this error: (VERI-1322) prefix of assignment pattern must be a data type How can this be corrected for the assignment "out_signal_q <= {8' {!

  16. Unpacked array concatenation assignment

    unpacked-array, assignment, SystemVerilog. stefaniecg November 28, 2016, 8:43am 1. Good Morning ! I'm failing to do a simple concatenation assignment to an unpacked array: parameter int c_data_width = 16; var logic [c_data_width-1:0] a; var logic [c_data_width-1:0] a_z [2:0]; so if i do this, it works. a_z [0] <= a; a_z [1] <= a_z [0]; a_z [2 ...

  17. Invalid assignment pattern SystemVerilog

    Invalid assignment pattern SystemVerilog Hi, i was trying to implement a floating point (single precision) adder. Vivado tells me that there is an error: [Synth 8-359] invalid assignment pattern basically where there is: EffectiveMantissa_A = {1'b1, A.Mantissa};). Can someone help me? (I even tried with the ' { } operand)

  18. system verilog

    ...items in an assignment pattern can be replicated using syntax, such as ' { n {element} }, and can be defaulted using the default: syntax. However, every element item in an array assignment pattern must be of the same type as the element type of the target array.