VLSI Design Lab Introduction By: Engr.Irshad Rahim Memon irshad.memon@isra.edu.pk

Outline Recommended Literature Difference between VLSI & VHDL Introduction to FPGA Introduction to VHDL Design EDA Tools VHDL VHDL Code Structure

Recommended Book Circuit Design With VHDL By: Volnei A. Pedroni e-copy available on electronics106.jimdo.com

Difference between VLSI and VHDL VHDL is a programming language that is used to test the functionalities or design of a circuit verilog is also a different language VLSI is a technology to miniaturization of chip, reducing power dissipation and timing delay. All these can be tested through software and FPGA implementation. VHDL is one of them so its necessary to go for VLSI in today's world.

Continued…. VHDL is a part of VLSI and these are interrelated to each other using VHDL supporting software you can develop your hardware Its a hardware description language so u must prefer for both VHDL and VLSI

What is Hardware Description Language? A hardware description language or HDL is any language for description and design of electronic circuits, and most commonly, digital logic. It can describe the circuit's operation, its design and organization, and tests to verify its operation by means of simulation.

What is Hardware Description Language? There are two primary purposes for hardware description languages Modeling of Digital Circuits: Having a model of the circuit allows for simulation and testing of the design for proper operation. Hardware description languages are used as one of the first steps in creating large digital integrated circuits.

HDLs for Analog Circuit Design Abbreviation Name Use AHDL Analog Hardware Descriptive Language  an open analog hardware description language Verilog-AMS Verilog for Analog and Mixed-Signal an open standard extending Verilog for analog and mixed analog/digital simulation

HDLs for Digital Circuit Design The two most widely-used and well-supported HDL varieties used in industry are Verilog and VHDL. Abbreviation Name Use ABEL Advanced Boolean Expression Language Hardware description language for implementing Boolean expressions AHDL Altera HDL a proprietary language from Altera Verilog verification logics most widely-used and well-supported HDL

HDL for Printed Circuit Board (PCB) Design Abbreviation Name Use PHDL PCB HDL a free and open source HDL for defining printed circuit board connectivity

WHAT IS FPGA? An FPGA is a device that consists of thousands or even millions of transistors connected to perform logic functions. They perform functions from simple addition and subtraction to complex digital filtering and error detection and correction. Aircraft, automobiles, radar, missiles, and computers are just some of the systems that use FPGAs Xilinx, Altera, are just a few companies that manufacture FPGAs. Even though there are several FPGA manufacturers, they all share the same basic architecture concept. It consists of three basic capabilities: input/output (I/O) interfaces, basic building blocks, and interconnections

Nexys2 Board (Xilinx Spartan 3E FPGA)

FPGA Design Flow Simulation with ISM simulator Design Synthesis Behavioral Simulation Functional simulation Entering VHDL code Design Synthesis Simulation with ISM simulator Design Implementation Physical Realization

DESIGN FLOW Design Entry: The design entry is the process of entering Digital logic expression or the Behavioral expression of desired statement or desired process. With the advance in technologies so many newer methods of designing entry are used for simplicity and faster designing. Xilinx ISE supports many different varieties of design entry, of which some are listed as: State machines Flow charts Block diagram/ interface based design (IBD) Hardware description languages (HDL) etc. Simulation: Simulation is the process of testing the logical or processing functionality of designed logic. Several kinds of Software and hardware Tools to provide this functionality. With Xilinx ISim Simulator you can simulate your design by writing “Test benches” and/or by assigning Manual wave flows to inputs and check functionality of outputs after simulation.  

Continued…. Synthesize: Synthesis is a process by which an abstract form of desired circuit behavior (typically register transfer level (RTL)) is turned into a design implementation in terms of logic gates. Synthesis is one aspect of electronic design automation. With Xilinx ISE Design Suite user can convert the HDL (hardware description language) or other kinds of designs created with Design entry tool into the Gate level design for any FPGA family. Physical Realization To physically implement the design in a CPLD or FPGA chip, a development kit is necessary. The development kit must be connected to a PC running ISE in order for the chip to be programmed.

EDA Tools There are several EDA (Electronic Design Automation) tools available for circuit synthesis, implementation, and simulation using VHDL. Some tools (place and route, for example) are offered as part of a vendor’s design suite (e.g., Altera’s Quartus II, which allows the synthesis of VHDL code onto Altera’s CPLD/FPGA chips, or Xilinx’s ISE suite, for Xilinx’s CPLD/FPGA chips).

Xilinx ISE Design Software: Introduction The ISE® software controls all aspects of the design flow. Through the Project Navigator interface, you can access all of the design entry and design implementation tools. You can also access the files and documents associated with your project.

Project Navigator Interface:

What is VHDL? The “V” in VHDL is short of yet another acronym: VHSIC or Very High-Speed Integrated Circuit. The HDL stands for Hardware Description Language. VHDL is a programming language that allows one to model and develop complex digital systems in a dynamic environment. VHDL is intended for circuit synthesis as well as circuit simulation.

What is VHDL? A fundamental motivation to use VHDL (or its competitor, Verilog) is that VHDL is a standard, technology/vendor independent language, and is therefore portable and reusable. The two main immediate applications of VHDL are in the field of Programmable Logic Devices (including CPLDs and FPGAs) and in the field of ASICs (Application Specific Integrated Circuits).

What is VHDL? Once the VHDL code has been written, it can be used either to implement the circuit in a programmable device (from Altera, Xilinx, Atmel, etc.) or can be submitted to a foundry for fabrication of an ASIC chip. Currently, many complex commercial chips (microcontrollers, for example) are designed using such an approach.

Translation of VHDL Code into a Circuit A VHDL code consists of ENTITY and ARCHITECTURE. ENTITY is description of I/O pins (ports) of the circuit. ARCHITECTURE describes how the circuit should function.

Translation of VHDL Code into a Circuit From the VHDL code a physical circuit is inferred. However, there are several ways of implementing the equations described in the ARCHITECTURE. The actual circuit will depend on the compiler/optimizer being used and, more importantly, on the target technology.

Translation of VHDL Code into a Circuit For instance, if our target is a programmable logic device (PLD or FPGA) then two possible results (among many others) for cout are illustrated in following figures.

Translation of VHDL Code into a Circuit On the other hand, if our target technology is an ASIC, then a possible CMOS implementation, at the transistor level, is that of following figure.

VHDL Code Structure As depicted in following figure, a standalone piece of VHDL code is composed of at least three fundamental sections:

VHDL Code Structure: Library Declaration Contains a list of all libraries to be used in the design. For example: ieee, std, work, etc. A LIBRARY is a collection of commonly used pieces of code. Placing such pieces inside a library allows them to be reused or shared by other designs.

VHDL Code Structure: Library Declaration To declare a LIBRARY (that is, to make it visible to the design) two lines of code are needed, one containing the name of the library, and the other a use clause, as shown in the syntax below. At least three packages, from three different libraries, are usually needed in a design: ieee.std_logic_1164 (from the ieee library), standard (from the std library), and work (work library).

VHDL Code Structure: Library Declaration Their declarations are as follows:

VHDL Code Structure: ENTITY An ENTITY is a list with specifications of all input and output pins (PORTS) of the circuit. Its syntax is shown below. The mode of the signal can be IN, OUT, INOUT, or BUFFER. IN and OUT are truly unidirectional pins, while INOUT is bidirectional. BUFFER, on the other hand, is employed when the output signal must be used (read) internally. The type of the signal can be BIT, STD_LOGIC, INTEGER, etc.

VHDL Code Structure: ENTITY Finally, the name of the entity can be basically any name, except VHDL reserved words. Let us consider the NAND gate. Its ENTITY can be specified as: The meaning of the ENTITY above is the following: The circuit has three I/O pins, being two inputs (a and b, mode IN) and one output (x, mode OUT). All three signals are of type BIT. The name chosen for the entity was nand_gate.

VHDL Code Structure: ARCHITECTURE The ARCHITECTURE is a description of how the circuit should behave (function). Its syntax is the following: An architecture has two parts: a declarative part (optional), where signals and constants (among others) are declared, and the code part (from BEGIN down). The name of an architecture can be basically any name (except VHDL reserved words), including the same name as the entity’s.

VHDL Code Structure: ARCHITECTURE Let us consider the NAND gate again. The meaning of the ARCHITECTURE above is the following: the circuit must perform the NAND operation between the two input signals (a, b) and assign (‘‘<=’’) the result to the output pin (x). The name chosen for this architecture was myarch. In this example, there is no declarative part, and the code contains just a single assignment.