Fpga Vhdl

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  • Topic: Field-programmable gate array, Logic gate, VHDL
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  • Published : January 11, 2013
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10-11-2012

Hardware Description Language (HDL)
VHDL for Specification

FPGA

VHDL for Simulation

VHDL for Synthesis

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Levels of design description

Register Transfer Level (RTL) Design Description

Algorithmic level Register Transfer Level Logic (gate) level Circuit (transistor) level Physical (layout) level Level of description most suitable for synthesis

FF

Combinational Logic

FF

Combinational Logic



Registers

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VHDL Design Styles
VHDL Design Styles

World of Integrated Circuits
Integrated Circuits
• Testbenches
Full-Custom ASICs Semi-Custom ASICs

dataflow

structural

behavioral

User Programmable

Concurrent statements

Components and interconnects

Sequential statements • Registers, counters, etc. • State machines

PLD

FPGA

PAL Subset most suitable for synthesis
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PLA

PML

LUT
(Look-Up Table)

MUX

Gates

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What is an FPGA?
• Field Programmable Gate Arrays • Field programmability is achieved through switches (Transistors are controlled by memory elements or fuses) • Switches control the following aspects • Interconnection among wire segments • Configuration of logic blocks

Why FPGAs?
• By the early 1980’s most of the logic circuits in typical systems where absorbed by a handful of standard large scale integrated circuits (LSI). • Microprocessors, bus/IO controllers, system timers,…..

• Every system still had the need for random “glue logic” to help connect the large ICs: • generating global control signals (for resets etc.) • data formatting (serial to parallel, multiplexing, etc.) EC3034 Modeling and Testing of Digital Systems – Monsoon 2012 7 EC3034 Modeling and Testing of Digital Systems – Monsoon 2012 8

Why FPGAs?
• Systems had a few LSI components and lots of small low density SSI (small scale IC) and MSI (medium scale IC) components.

Why FPGAs?
• Custom ICs where sometimes designed to replace the large amount of glue logic: • reduced system complexity and manufacturing cost, improved performance. • However, custom ICs are relatively very expensive to develop, and delay in introduction of product to market (time to market) because of increased design time.

• Note: need to worry about two kinds of costs:
• cost of development, sometimes called non-recurring engineering (NRE) • cost of manufacture EC3034 Modeling and Testing of Digital Systems – Monsoon 2012 9 EC3034 Modeling and Testing of Digital Systems – Monsoon 2012 10

Why FPGAs?
• Therefore the custom IC approach was only viable for products with very high volume (where NRE could be amortized), and which were not time to market sensitive. • FPGAs were introduced as an alternative to custom ICs for implementing glue logic: • improved density relative to discrete SSI/MSI components (within around 10x of custom ICs) • with the aid of computer aided design (CAD) tools circuits could be implemented in a short amount of time (no physical layout process, no mask making, no IC manufacturing)

Two competing implementation approaches

ASIC Application Specific Integrated Circuit
• designed all the way from behavioral description to physical layout • designs must be sent for expensive and time consuming fabrication in semiconductor foundry

FPGA Field Programmable Gate Array
• no physical layout design; design ends with a bitstream used to configure a device • bought off the shelf and reconfigured by designers themselves 12

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10-11-2012

FPGAs vs ASICs
ASICs FPGAs
Off-the-shelf High performance Low development costs Low...
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