Fpga 04-verilog-programming
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The document discusses hardware description languages (HDLs) and Verilog programming. It states that two widely used HDLs are Verilog and VHDL. Verilog is more popular than VHDL for FPGA programming. The document then provides details on the history, functions, and usage of Verilog. It explains that Verilog can be used to model circuits at different levels of abstraction, from transistor level to behavioral level. Register transfer level modeling combines behavioral and dataflow modeling, which is suitable for FPGA design. Several examples of Verilog code for gate level and dataflow modeling are also presented.
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Fpga 04-verilog-programming
- 1. ENGR. RASHID FARID CHISHTI LECTURER,DEE, FET, IIUI CHISHTI@IIU.EDU.PK WEEK 4 VERILOG PROGRAMMING FPGA Based System Design Sunday, May 17, 2015 1 www.iiu.edu.pk
- 2. A hardware description language is a computer language that is used to describe hardware. Currently, almost all integrated circuits are designed with using HDL. Two HDLs are widely used Verilog HDL VHDL (Very High Speed Integrated Circuit Hardware Description Language) Schematic design entry can be replaced by writing HDL code that CAD tools understand. CAD tools can verify the HDL codes, and create the circuits automatically from HDL codes. Hardware Description Language Sunday, May 17, 2015www.iiu.edu.pk 2
- 3. We use Verilog, not VHDL for FPGA programming Verilog is more popular in industry than VHDL They offer similar features History of Verilog In 1980s, originally developed by Gateway Design Automation. In 1990, was put in public domain. In 1995, adopted as an IEEE standard 1364-1995 In 2001, an enhanced version, Verilog 2001 Functions of Verilog Design entry, like schematic Simulation and verification of your design Synthesis Facts About Verilog Sunday, May 17, 2015www.iiu.edu.pk 3
- 4. Verilog may be used to model circuits and behaviors at various levels of abstraction: Transistor/Switch Level Modeling. LOW LEVEL Gate Level Modeling. Data Flow Modeling. Behavioral or algorithmic Modeling. HIGH LEVEL For design with FPGA devices, transistor and gate level modeling is not appropriate. Register Transfer Level (RTL) is a combination of behavioral and dataflow Modeling. Verilog Usage Sunday, May 17, 2015www.iiu.edu.pk 4
- 5. //Define inverter module my_not(out, in); output out; input in; // declare power // and ground supply1 pwr; supply0 gnd; //instantiate nmos // and pmos switches pmos (out, pwr, in); nmos (out, gnd, in); endmodule Switch Level Modeling Sunday, May 17, 2015www.iiu.edu.pk 5
- 6. // A simple example module gate1 (a,b,c); input a,b; output c; and (c,a,b); endmodule Modules are the basic building blocks in Verilog. A logic circuit module, Its ports: inputs and outputs Begins with module, ends with endmodule A Simple Verilog Example Sunday, May 17, 2015www.iiu.edu.pk 6 comment line module name port list end module port declarations a b c gate1
- 7. module eg1 (a,b,c,f); input a,b,c; output f; wire g,h,i; and (g,a,b); not (h,b); and (i,h,c); or (f,g,i); endmodule Gate Level Modeling vs Data Flow Modeling Sunday, May 17, 2015www.iiu.edu.pk 7 // Data Flow Modeling module ex1 (a,b,c,f); input a,b,c; output f; assign f = (a&b) | (~b&c); endmodule // Data Flow Modeling module ex1 (a,b,c,f); input a,b,c; output f; assign f = (a&b) | (~b&c); endmodule a c F = AB + B'C b fg ih
- 8. Writing Test Bench Sunday, May 17, 2015www.iiu.edu.pk 8 /* testbench for ex1 block *//* testbench for ex1 block */ modulemodule ex1_tb ;ex1_tb ; wirewire f1;f1; regreg a1, b1, c1;a1, b1, c1; ex1 my_module(a1, b1, c1, f1);ex1 my_module(a1, b1, c1, f1); initialinitial beginbegin $monitor$monitor(($time$time," ", a1, b1,," ", a1, b1, c1, ," ", f1);c1, ," ", f1); a1 = 1'ba1 = 1'b00; b1 = 1'b; b1 = 1'b11; c1 = 1'b; c1 = 1'b00;; #5#5 a1 = 1'ba1 = 1'b11; b1 = 1'b; b1 = 1'b11; c1 = 1'b; c1 = 1'b11;; #5#5 a1 = 1'ba1 = 1'b11; b1 = 1'b; b1 = 1'b00; c1 = 1'b; c1 = 1'b11;; #5#5 a1 = 1'ba1 = 1'b11; b1 = 1'b; b1 = 1'b11; c1 = 1'b; c1 = 1'b11;; #10#10 $finish$finish;; endend endmoduleendmodule /* testbench for ex1 block *//* testbench for ex1 block */ modulemodule ex1_tb ;ex1_tb ; wirewire f1;f1; regreg a1, b1, c1;a1, b1, c1; ex1 my_module(a1, b1, c1, f1);ex1 my_module(a1, b1, c1, f1); initialinitial beginbegin $monitor$monitor(($time$time," ", a1, b1,," ", a1, b1, c1, ," ", f1);c1, ," ", f1); a1 = 1'ba1 = 1'b00; b1 = 1'b; b1 = 1'b11; c1 = 1'b; c1 = 1'b00;; #5#5 a1 = 1'ba1 = 1'b11; b1 = 1'b; b1 = 1'b11; c1 = 1'b; c1 = 1'b11;; #5#5 a1 = 1'ba1 = 1'b11; b1 = 1'b; b1 = 1'b00; c1 = 1'b; c1 = 1'b11;; #5#5 a1 = 1'ba1 = 1'b11; b1 = 1'b; b1 = 1'b11; c1 = 1'b; c1 = 1'b11;; #10#10 $finish$finish;; endend endmoduleendmodule module ex1 (a,b,c,f); input a,b,c; output f; assign f=(a&b)|(!b&c); endmodule module ex1 (a,b,c,f); input a,b,c; output f; assign f=(a&b)|(!b&c); endmodule Each signal in Verilog belongs to either a net or a register A net (wire) represents a physical wire. Its signal value is determined by its driver. If it is not driven by any driver, its value is high impedance (Z). A register is like a variable in programming languages. It keeps its value until a new value is assigned to it. Unlike registers, nets do not have storage capacity. Each signal in Verilog belongs to either a net or a register A net (wire) represents a physical wire. Its signal value is determined by its driver. If it is not driven by any driver, its value is high impedance (Z). A register is like a variable in programming languages. It keeps its value until a new value is assigned to it. Unlike registers, nets do not have storage capacity. print to a console
- 9. Verilog supports basic logic gates as predefined primitives. There are two classes of basic gates: and/or gates and buf/not gates. And/or gates have one scalar output and multiple scalar inputs The first terminal in the list of gate terminals is an output and the other terminals are inputs. Example 1: Gate Instantiation of And/Or Gates wire OUT, IN1, IN2; and a1(OUT, IN1, IN2); xnor (OUT, IN1, IN2); // More than two inputs; // 3 input nand gate nand (OUT, IN1, IN2, IN3); Basic Gates Sunday, May 17, 2015www.iiu.edu.pk 9
- 10. Truth Tables for And/Or Gates Sunday, May 17, 2015www.iiu.edu.pk 10 and 0 1 x z or 0 1 x z xor 0 1 x z 0 0 0 0 0 0 0 1 x x 0 0 1 x x 1 0 1 x x 1 1 1 1 1 1 1 0 x x x 0 x x x x x 1 x x x x x x x z 0 x x x z x 1 x x z x x x x nand 0 1 x z nor 0 1 x z xnor 0 1 x z 0 1 1 1 1 0 1 0 x x 0 1 0 x x 1 1 0 x x 1 0 0 0 0 1 0 1 x x x 1 x x x x x 0 x x x x x x x z 1 x x x z x 0 x x z x x x X 1=True , 0=False, X=Unknown, Z=High impedance
- 11. Buf/not gates have one scalar input and one or more scalar outputs The last terminal in the port list is connected to the input. Other terminals are connected to the outputs Basic buf/not gate primitives in verilog are buf not Buf/not gates with additional control signal are bufif1, notif1, bufif0, notif0 Buf/Not Gates Sunday, May 17, 2015www.iiu.edu.pk 11 buf not input output input output 0 0 0 1 1 1 1 0 x x x x z x z x
- 12. The L and H symbols have a special meaning. The L symbol means the output has 0 or z value. The H symbol means the output has 1 or z value. Any transition to H or L is treated as a transition to x. Examples //Instantiation of bufif gates. bufif1 b1 (out, in, ctrl); bufif0 b0 (out, in, ctrl); //Instantiation of notif gates notif1 n1 (out, in, ctrl); notif0 n0 (out, in, ctrl); x={0,1,z} L={0,z} H={1,z} bufif1 Ctrl notif1 Ctrl 0 1 x z 0 1 x z in 0 z 0 L L in 0 z 1 H H 1 z 1 H H 1 z 0 L L x z x x x x z x x x z z x x x z z x x x bufif0 Ctrl notif0 Ctrl 0 1 x z 0 1 x z in 0 0 z L L in 0 1 z H H 1 1 z H H 1 0 z L L x x z x x x x z x x z x z x x z x z x x Truth Table for bufif/notif Gates Sunday, May 17, 2015www.iiu.edu.pk 12
Editor's Notes
- #5: Behavioral or algorithmic level This is the highest level of abstraction provided by Verilog HDL. A module can be implemented in terms of the desired design algorithm without concern for the hardware implementation details. Designing at this level is very similar to C programming. Dataflow level At this level, the module is designed by specifying the data flow. The designer is aware of how data flows between hardware registers and how the data is processed in the design. Gate level The module is implemented in terms of logic gates and interconnections between these gates. Design at this level is similar to describing a design in terms of a gate-level logic diagram. Switch level This is the lowest level of abstraction provided by Verilog. A module can be implemented in terms of switches, storage nodes, and the interconnections between them. Design at this level requires knowledge of switch-level implementation details. Verilog allows the designer to mix and match all four levels of abstractions in a design. In the digital design community, the term register transfer level (RTL) is frequently used for a Verilog description that uses a combination of behavioral and dataflow constructs and is acceptable to logic synthesis tools.