FPGA Prototyping by VHDL Examples

Xilinx MicroBlaze MCS SoC

Pong P. Chu

• Publisher: Wiley
• Year: 2018
• ISBN:
  9781119282761
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

A hands-on introduction to FPGA prototyping and SoC design

This Second Edition of the popular book follows the same "learning-by-doing" approach to teach the fundamentals and practices of VHDL synthesis and FPGA prototyping. It uses a coherent series of examples to demonstrate the process to develop sophisticated digital circuits and IP (intellectual property) cores, integrate them into an SoC (system on a chip) framework, realize the system on an FPGA prototyping board, and verify the hardware and software operation. The examples start with simple gate-level circuits, progress gradually through the RT (register transfer) level modules, and lead to a functional embedded system with custom I/O peripherals and hardware accelerators. Although it is an introductory text, the examples are developed in a rigorous manner, and the derivations follow strict design guidelines and coding practices used for large, complex digital systems.

The new edition is completely updated. It presents the hardware design in the SoC context and introduces the hardware-software co-design concept. Instead of treating examples as isolated entities, the book integrates them into a single coherent SoC platform that allows readers to explore both hardware and software "programmability" and develop complex and interesting embedded system projects. The revised edition:

• Adds four general-purpose IP cores, which are multi-channel PWM (pulse width modulation) controller, I 2 C controller, SPI controller, and XADC (Xilinx analog-to-digital converter) controller.
• Introduces a music synthesizer constructed with a DDFS (direct digital frequency synthesis) module and an ADSR (attack-decay-sustain-release) envelop generator.
• Expands the original video controller into a complete stream-based video subsystem that incorporates a video synchronization circuit, a test pattern generator, an OSD (on-screen display) controller, a sprite generator, and a frame buffer.
• Introduces basic concepts of software-hardware co-design with Xilinx MicroBlaze MCS soft-core processor.
• Provides an overview of bus interconnect and interface circuit.
• Introduces basic embedded system software development.
• Suggests additional modules and peripherals for interesting and challenging projects.

The FPGA Prototyping by VHDL Examples, Second Edition makes a natural companion text for introductory and advanced digital design courses and embedded system course. It also serves as an ideal self-teaching guide for practicing engineers who wish to learn more about this emerging area of interest.

Part I
BASIC DIGITAL CIRCUITS DEVELOPMENT

CHAPTER 1
GATE-LEVEL COMBINATIONAL CIRCUIT

HDL (hardware description language) is used to describe and model digital systems. VHDL is one of the two major HDLs. In this chapter, we use a simple comparator to illustrate the skeleton of a VHDL program. The description uses only logical operators and represents a gate-level combinational circuit, which is composed of simple logic gates.

1.1 OVERVIEW OF VHDL

VHDL stands for “VHSIC (very high-speed integrated circuit) hardware description language.” It was originally sponsored by the U.S. Department of Defense and later transferred to the IEEE (Institute of Electrical and Electronics Engineers). The language is formally defined by IEEE Standard 1076. The standard was first ratified in 1987 and revised several times. The main versions are referred to as VHDL-87, VHDL-93, VHDL-2000, and VHDL-2008. The synthesis subset does not change significantly after VHDL-93 and this book mainly follows VHDL-93.

VHDL is intended for describing and modeling a digital system at various levels and is an extremely complex language. The focus of this book is on hardware design rather than the language. Instead of covering every aspect of VHDL, we introduce the key VHDL synthesis constructs by examining a collection of examples. Detailed VHDL coverage may be explored through the sources listed in the Bibliographic Notes section.

In this chapter, we introduce the HDL concepts, basic VHDL language constructs, logical operators, and program structure. A simple gate-level combinational circuit is used for demonstration. In Chapter 3, we cover the more sophisticated VHDL operators and constructs and examine module-level combinational circuits, which are composed of intermediate-sized components, such as adders, comparators, and multiplexers.

1.2 GENERAL DESCRIPTION

Consider a 1-bit equality comparator with two inputs, i0 and i1, and an output, eq. The eq signal is asserted when i0 and i1 are equal. The truth table of this circuit is shown in Table 1.1.

Table 1.1 Truth table of a 1-bit equality comparator

input i0 i1	output eq
0 0	1
0 1	0
1 0	0
1 1	1

Assume that we want to use basic logic gates, which include not, and, or, and xor cells, to implement the circuit. One way to describe the circuit is to use a sum-of-products format. The logic expression is

One possible corresponding VHDL code is shown in Listing 1.1. We examine the language constructs and statements of this code in the following subse...