FPGAs AND EMBEDDED SYSTEMS

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FPGAs AND EMBEDDED SYSTEMS

• Asma Fathima Khizer
• University Of North Carolina Charlotte

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Overview

• Introduction
• Technical overview
• Configuration
• Embedded System design in FPGA
• Processors
• Applications

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What are FPGAs?

• A Field Programmable Gate Array or FPGA is a
  semiconductor device containing programmable
  logic components and programmable interconnects.
• FPGAs are programmable digital logic chips. It
  means that we can program them to do almost any
  digital function.
• In most FPGAs, these programmable logic
  components (or logic blocks) also include memory
  elements, which may be simple flip-flops or more
  complete blocks of memories.

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Architecture

• Basic architecture consists of an array of
  configurable logic blocks (CLBs) and routing
  channels.
• A logic-cell (CLB) is composed of a small lookup
  table, some gates and a D-flip-flop. Each
  logic-cell then can be connected to other
  logic-cells through interconnect resources.

Fig Logic-cell (CLB)
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Architecture Contd.,

• Each wiring segment spans only one logic block
  before it terminates in a switch box.
• Whenever a vertical and a horizontal channel
  intersect there is a switch box.
• When a wire enters a switch box, there are three
  programmable switches that allow it to connect to
  three other wires in adjacent channel segments.

Fig Switch box topology
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Architecture Contd.,
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FPGA Pins

• FPGA pins fall into 2 categories
• Dedicated pins
• User pins
• About 20 to 30 of the pins of an FPGA are
  "dedicated pins", which means that they are
  hard-coded to a specific function.

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FPGA Pins Contd.,

• Dedicated Pins are again classified into 3
  categories
• Power pins. Might be ground pins (GND) or power
  pins (core or IO).
• Configuration pins. These pins are used to
  "download" the FPGA.
• Dedicated inputs, or clock pins. These pins are
  able to drive large and wide nets inside the
  FPGA, suitable for clocks or signals with large
  fan-outs.
• The rest are user pins.

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Clocks and Global lines

• An FPGA design is usually "synchronous". Its
  means that the design is clock based - each clock
  allows the D-flip flops to take a new state.
• Global routing or Global lines, these allow
  distributing the clock signal all over the FPGA
  with a low skew (i.e. the clock signal appears
  almost simultaneously to all the flipflops).
• To feed a clock to FPGA, a dedicated input pin is
  used
• An FPGA can use multiple clocks

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Pin Assignments

• Xilinx (uses .ucf files)
• NET "data" LOC "P17"NET "clock" LOC
  "P91"
• Altera (uses .qsf files)
• set_location_assignment PIN_10 -to
  clkset_location_assignment PIN_26 -to LED

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FPGA Configuration

• An FPGA can be into 2 states
• Configuration mode
• User mode

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FPGA Configuration

• Configuring an FPGA means downloading a stream of
  0's and 1's into it through some special pins.
  Once the FPGA is configured, it goes into
  "user-mode" and becomes active, performing
  accordingly to your programmed logic function
• There are 3 ways to configure FPGA
• Use a cable from a PC to the FPGA, and run a
  software on the PC to send data through the
  cable.
• Use a microcontroller on the board, with an
  adequate firmware to send data to the FPGA.
• Use a "boot-PROM" on the board, connected to the
  FPGA, that configures the FPGA automatically at
  power-up.

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FPGA Programming

• The behavior of the FPGA (logic function) can be
  defined by either a hardware description language
  (HDL) or a schematic design.
• Compile the logic function on the PC using the
  software provided by the FPGA vendor. A binary
  file is created.
• Connect a cable from the PC to the FPGA and
  download the binary file.
• FPGAs loose their functionality when the power
  goes away (like RAM in a computer that looses its
  content). We have to re-download them when power
  goes back up to restore the functionality.

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A simple program for D- Flip Flop

• library IEEE
• use IEEE.std_logic_1164.all
• entity DFlipFlop is
• port (
• CLK in STD_LOGIC
• RST in STD_LOGIC
• D in STD_LOGIC
• Q out STD_LOGIC
• )
• end DFlipFlop
• architecture behaviour of DFlipFlop is
• begin
• process(CLK)
• begin
• if rising_edge(CLK) then
• if RST '1' then
• Q lt '0'

Ref 6
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FPGA vs. Microcontrollers

• Microcontrollers are based on a CPU architecture.
  As all CPUs, they execute instructions in a
  sequential manner.
• FPGAs are programmable logic and run in a
  parallel fashion.

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FPGA Manufacturers

• Xilinx has traditionally been the FPGA leader.
• Altera is the second FPGA heavyweight.
• Lattice Semiconductor focuses on low-cost,
  feature-optimized FPGAs and non-volatile,
  flash-based FPGAs.
• Actel has antifuse and reprogrammable flash-based
  FPGAs.
• QuickLogic has antifuse (programmable-only-once)
  products.
• Cypress Semiconductor
• Atmel is the only manufacturer whose devices are
  fine-grain reconfigurable (the Xilinx XC62xx
  were, but they are no longer in production). They
  focus on providing AVR Microcontrollers with FPGA
  fabric on the same die. These factors aside,
  their devices tend to be smaller and more
  expensive than other manufacturers'.
• Achronix Semiconductor has very fast FPGAs in
  development. They plan to ship in early 2007 and
  claim they can reach speeds of over 1GHZ.

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Embedded System Design in an FPGA

• A typical digital system design involves a
  significant amount of custom logic circuitry, but
  also includes pre-designed major components, such
  as processors, memory units and various types of
  input/output (I/O) interfaces.
• In the traditional approach for designing such
  systems, a new integrated circuit (IC) chip is
  created for the custom logic circuits, but each
  pre-designed component is included as a separate
  chip
• Different approach for realizing digital systems,
  called embedded system design. It leverages the
  advanced capabilities of today's IC technology by
  implementing many of the components of the system
  within a single chip, such as a field
  programmable gate array (FPGA).

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Technical reasons to use FPGAs in System Design

• Offer large logic capacity, exceeding several
  million equivalent logic gates, and include
  dedicated memory resources
• Include special hardware circuitry that is often
  needed in digital systems, such as digital signal
  processing (DSP) blocks (with multiply and
  accumulate functionality) and phase-locked loops
  (PLLs) (or delay-locked loops (DLLs)) that
  support complex clocking schemes
• Support a wide range of interconnection
  standards, such as double data rate (DDR SRAM)
  memory, PCI and high-speed serial protocols.

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Processors

• Two types of processors are available to use in
  FPGA
• Hard Processors
• Soft Processors
• Hard Processor
• A pre-designed circuit that is fabricated within
  the FPGA chip
• Soft Processor
• The processor exists as code written in a
  hardware description language (HDL)

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Advantages of Soft Processors

• More flexible compared to hard processor.
• Resources are consumed for processor only when
  they are actually needed in the system.
• Multiple soft processors can be included in the
  FPGA when desired.

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Embedded system design software tools

• Two main aspects to the software tools
• The creation of the system hardware
• The development of software that runs on the
  processors included in the system.
• For creating the hardware circuitry, the tools
  allow the user to build a system by making use of
  pre-designed building blocks for processors,
  memory controllers, digital signal processing
  circuits and various communication modules (such
  as UARTs).
• The software allows easy instantiation of these
  sub-circuits and can automatically interconnect
  them on the FPGA chip.
• The Electronic Design Automation tools generate
  memory maps for the system, allowing the
  processor(s) to access the systems hardware
  resources.

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Embedded Software Design Flow for the Nios II
Processor
Ref 3
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Applications

• Applications of FPGAs include DSP,
  software-defined radio, aerospace and defense
  systems, ASIC prototyping, medical imaging,
  computer vision, speech recognition,
  cryptography, bioinformatics, computer hardware
  emulation and a growing range of other areas.
  They now find applications in any area or
  algorithm that can make use of the massive
  parallelism offered by their architecture.
• Reconfigurable computing is computer processing
  with highly flexible computing fabrics. The
  principal difference when compared to using
  ordinary microprocessors is the ability to make
  substantial changes to the data path itself in
  addition to the control flow.

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References

• http//en.wikipedia.org/wiki/FPGA
• http//en.wikipedia.org/wiki/Embedded_System_Desig
  n_in_an_FPGA
• http//www.fpga4fun.com/WhatAreFPGAs.html
• http//en.wikipedia.org/wiki/Reconfigurable_comput
  ing
• http//www.qa-talk.com/news/alt/alt100.html
• http//en.wikipedia.org/wiki/Vhdl

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THANK YOU