Introduction

Complex circuits are commonly designed using a top down methodology. Various specification levels are required at each stage of the design process. As an example, at the architectural level, a specification may correspond to a block diagram or an Algorithmic State Machine (ASM) chart. A block or ASM stage corresponds to a register transfer block (for example register, adder, counter, multiplexer, glue logic, finite state machine) where the connections are N-bit wires. Use of an HDL language like Verilog allows expressing notations such as ASM charts and circuit diagrams in a computer language. Verilog provides both behavioral and structural language structures which allow expressing design objects at high and low levels of abstraction. Designing hardware with a language like Verilog allows usage of software concepts such as parallel processing and object-oriented programming. Verilog has a syntax similar to C and Pascal, and is supported by XST as IEEE 1364.

The Verilog support in XST provides an efficient way to describe both the global circuit and each block according to the most efficient "style." Synthesis is then performed with the best synthesis flow for each block. Synthesis in this context is the compilation of high-level behavioral and structural Verilog HDL statements into a flattened gate-level netlist, which can then be used to custom program a programmable logic device such as the Virtex™ FPGA family. Different synthesis methods are used for arithmetic blocks, glue logic, and finite state machines.

This manual assumes that you are familiar with the basic notions of Verilog. Please refer to the IEEE Verilog HDL Reference Manual for a complete specification.