If number_of_levels is 0, it will dump all signals instantiated under instance_name at any level. . In the examples below, suppose you have an instance called reg_file in an instance called data_path in an instance called exec_core in your top module. Dumpvars (0, g_file dumpvars (2, top. Exec_core the first statement will dump all wires and registers instantiated at any level under the module called reg_file. The second statement will dump all wires and registers instantiated in the top level of exec_core, and the top level of data_path, or any other modules instantiated in exec_core. Timing information you will need to examine the library files to figure out the timing delays of the library modules. . Below is an example of a module from the library. .
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8.4 readmemb and readmemh These are used for reading in data from a file of binary or hex numbers to initialize a memory module. . you can use it like this: initial begin readmemb filename instance_name. Mem, professor starting_address end starting_address is the address of the memory module where you begin initialization. . If starting_address is greater than football zero, the memory locations at the beginning will remain unitialized (logic value x). . The data file is just a text file that contains a list of binary or hex numbers. . An example of a data file will be given later in the semester. 8.5 Dumping waveforms (for creating a waveform file in text format using vcs) dumpfile is used to specify the name of the waveform file. Dump dumpvars specifies the wires and registers whose values you want to record. . The syntax is dumpvars ( number_of_levels, instance_name if number_of_levels is 1, it will dump all the signals instantiated in the top level of the instance specified. . If number_of_levels is greater than 1, it will dump all signals instantiated number_of_levels levels hierarchically below the specified instance. .
you may find some of these useful:.1 finish Use finish to end the simulation after a specified amount of time. . Example: initial 1000 finish; Stops the simulation after 1000 time units. . Unless you are stepping through the simulation interactively using VirSim, essays you will need to use finish. 8.2 time returns the current simulation time. 8.3 strobe Use strobe to display a message on your screen. . The format is similar to that of printf. . Note that if the strobe command is called at the same simulation time that other registers or wires are changing values, the value changes will happen before the strobe command is executed. . Example: always posedge clk) strobe at time 0d, a b time, a this statement is executed every time clk transitions from 0 to 1, printing the simulation time in decimal and the value of a in binary. . If a changed right at the clock edge, the new value would be printed.
Compiler Directives you can use an accent grave followed by a keyword to control compilation and simulation. . The compiler directive is not followed by a semicolon. 7.1 define The define keyword can be used for making text macros. During write compilation, when the macro name is preceded by an accent grave, the compiler substitutes the macro text. . Here are a couple of examples: reg clk; reg 1:0 a; define half_cycle 5 define set_a reviews 10 a 2'b always half_cycle) clk clk; initial begin clk 1'b0; set_a 00; set_a 01; set_a 10; set_a 11; end /initial begin In the example above, the value. 7.2 include This is used to include more source files. System Tasks and Functions System tasks are commands built into the simulator. . The system task calls end with a semicolon. .
If you have more than one initial block in your code, they will be executed concurrently. 6.2 Always Always descriptions will execute repeatedly throughout a simulation. To initialize and cycle a clock at 10 time units, you could do the following: reg clk; initial clk 1'b0; always 5 clk clk; /clock cycle is 10.3 Repeat The repeat statement can be used to specify how many times a begin-end block. The block following the repeat statement is executed the number of times indicated by the expression in parenthesis following the block keyword. . In the following example, the block is executed four times. . Note that i added a time delay after the last statement in the block to avoid a race condition. Reg 3:0 A; initial begin repeat(4) begin a 4'hf; 10 /delay 10 time units a 0; 10 /delay 10 time units a 4'h5; 10 /delay 10 time units end /end repeat(4) end /initial description.
Verilog case statement example
Examples: wire a, b, c; assign a b; assign c b; /c is assigned to not b With a continuous assignment, whenever the value of a variable on the right-hand side changes, the expression is re-evaluated and the value of the left-hand side is updated. . The left-hand side of the assignment must be a wire. Procedural Assignments (for regs).1 Initial you will use registers primarily in testing your code. . Unlike wires, regs will hold a value until it is re-assigned. . In other words, it maintains state. . Delays, indicated by a number following a pound sign, can be used to specify an amount of time before the value held by the reg changes. . Here is an example.
Reg 3:0 A; initial begin a 4'hf; 10 /delay 10 time units a 0; 10 /delay 10 time units a 4'h5; end day /end initial description This example makes procedural assignments to register. . Any code in a begin-end block following the initial keyword executes only once, starting at the beginning (time 0) of a simulation. . The first assignment to register a is made at time. . The 10 indicates a delay of 10 time units before the next essay assignments are made. . a is set to 0 at time 10, and a is set to 5 at time. An initial description may be used without a block delimited by begin and end if there is only one statement (see example in next section). Note that your code can have multiple procedural assignments.
Ports may be either scalar or vector. . The port names in the declarations do not have to occur in the same order as they did in the port list. The body of the module (consisting of wire and reg declarations and module instances) follow the port declarations. Here is an example of a module definition for a gated D-latch: / / gateatch / module d_latch (d, q, qbar, wen input d, wen; output q, qbar; wire dbar, r, s; inv1 inv1 (dbar, d nand2 nand1 (s, d, wen nand2 nand2 (r, dbar. inv1 and nand2 (1-input inverter and 2-input nand gate) are modules that are defined in the class libraries. .
For both of these gates, the first port is the output of the gate, and the remaining ports are inputs. A module instance consists of the module name followed by an instance identifier, port list, and semicolon. . several instantiations of the same type of module can be made in a list like this: nand2 nand1 (s, d, wen nand2 (r, dbar, wen nand3 (q, s, qbar nand4 (qbar, r, q When instantiating a module, you can omit ports from the port list. For example, if we wanted to instantiate d_latch in another module but did not care about the qbar output, we could instantiate it as follows: d_latch latch1 (din, q_out, wen In this example, din and wen could be either wires, registers, or ports declared. You should know that any undeclared identifiers are implicitly declared as scalar wires. . so watch out for typos in your port lists. Continuous assignments (for wires) assign can be used to tie two wires together or to continually assign a behavioral expression to a wire. .
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You can specify repetition by putting a number before the opening brace, like this: 4Byte0 is the same thing as Byte0, byte0, byte0, byte0. A 2-dimensional memory of business type reg can be declared as follows: reg 7:0 memory 0:1023; you can reference bytes of memory as memory5, for example. If you want to reference an individual bit, you must first copy the byte into another variable. We are using 4-value logic; that is, each bit can take on one of four possible values: 0: logic 0 1: logic 1 z: high impedance (for tri-state driver output) x: unknown or undefined. Module definitions and instances The module is the basic logic entity in Verilog. A module definition is delimited by the keywords module and endmodule, as shown in the example below. The module header consists of the module keyword, the name of the module, and the port list in parenthesis, followed by a semicolon: module d_latch (d, q, qbar, wen following the module header are the port declarations. Ports may be of type input, output, or inout, for input, output, or bidirectional ports. .
Wires cannot hold a value; they are used to connect modules of essay combinational logic. . Regs are used to store values. Since regs keep state, a reg cannot be the output of combinational logic. Note: The reg datatype is not what you use to make flip-flops and registers. . When implemented at the structural level, flip-flops and registers are still made out of wires and logic gates or other modules, as you will see in the d-latch example in section. . Regs are only used in behavioral Verilog. You can declare regs and wires as follows: reg a, b; /two scalar registers reg 0:7 Byte; /8-bit vector, bit 0 is msb wire 31:0 Word; /32-bit vector, bit 31 is msb you can reference a subset of bits in a vector as Word0. You can use braces for concatenating two or more signals, like this: Word7:0, word31:8 is the 32-bit vector obtained by rotating Word to the right by one byte. 24'b0, word7:0 is the 32-bit vector obtained by zero extending the first byte of Word.
debugging purposes. This manual will cover all aspects of the verilog language that you will need to be familiar with. Syntax, verilog uses a c-like syntax. . It is case sensitive, and all keywords are in lower case letters. . Declarations, assignments, and statements end with a semicolon. . It also uses C-style comments: / comment to end of line closed comment numbers are represented as number_of_bits ' base number, where base can be b, o, d, or h, for binary, octal, decimal, or hex, respectively. . Some examples: 8'hFF /8-bit hex number 5'b101 /5-bit binary number 00101 1 /decimal number. . (decimal is the default base) 3'o5 /3-bit octal number. Data types The data types that you will use are reg (register) and wire.
Module definitions and instances. System, tasks and Functions. Introduction, this semester, you will design your project using Verilog hdl, a hardware description language commonly used in industry. . Verilog can be used to describe designs at a high level of abstraction, you will design your processor at the gate level in order to quantify the complexity and timing requirements of your design. . Hence you will use structural Verilog only. You will be provided Verilog libraries containing modules that will be the basic building blocks for your design. . These library parts include simple logic gates, registers, and memory modules, for example. While the library parts are designed behaviorally, they incorporate some timing information that will be used in your simulations. . Using the class libraries ensures a uniform timing standard for everyone.
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Stack Exchange network, stack Exchange network consists of 174 q a communities including. Stack overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. History 3, updated by, sergey smolov over 1 year ago, status changed from, verified. Closed, done changed from 0 to 100, detected in build changed from svn to master, published in build set to 20161025, also available in: Atom, pDF. EE382n verilog Manual,. Department of Electrical and Computer Engineering. The remote University of Texas at Austin. Spring, 2004, table of Contents.