A FIELD-PROGRAMMABLE GATE ARRAY (FPGA) is an integrated circuit
designed to be configured by a customer or a designer after
manufacturing – hence "field-programmable ". The FPGA configuration
is generally specified using a hardware description language (HDL),
similar to that used for an application-specific integrated circuit
(ASIC). (Circuit diagrams were previously used to specify the
configuration, as they were for ASICs, but this is increasingly rare.)
A Spartan FPGA from
FPGAs contain an array of programmable logic blocks , and a hierarchy of reconfigurable interconnects that allow the blocks to be "wired together", like many logic gates that can be inter-wired in different configurations. Logic blocks can be configured to perform complex combinational functions , or merely simple logic gates like AND and XOR . In most FPGAs, logic blocks also include memory elements, which may be simple flip-flops or more complete blocks of memory.
* 1 Technical design
* 2 History
* 2.1 21st Century Developments * 2.2 Gates * 2.3 Market size * 2.4 Design starts
* 3 Comparisons
* 3.1 Complex programmable logic devices (CPLD) * 3.2 Security considerations
* 4 Applications
* 5 Architecture
* 5.1 Logic blocks * 5.2 Hard blocks * 5.3 Clocking * 5.4 3D architectures
* 6 Design and programming * 7 Basic process technology types * 8 Major manufacturers * 9 See also * 10 References * 11 Further reading * 12 External links
Contemporary field-programmable gate arrays (FPGAs) have large resources of logic gates and RAM blocks to implement complex digital computations. As FPGA designs employ very fast I/Os and bidirectional data buses, it becomes a challenge to verify correct timing of valid data within setup time and hold time. Floor planning enables resources allocation within FPGAs to meet these time constraints. FPGAs can be used to implement any logical function that an ASIC could perform. The ability to update the functionality after shipping, partial re-configuration of a portion of the design and the low non-recurring engineering costs relative to an ASIC design (notwithstanding the generally higher unit cost), offer advantages for many applications.
Some FPGAs have analog features in addition to digital functions. The most common analog feature is programmable slew rate on each output pin, allowing the engineer to set low rates on lightly loaded pins that would otherwise ring or couple unacceptably, and to set higher rates on heavily loaded pins on high-speed channels that would otherwise run too slowly. Also common are quartz-crystal oscillators, on-chip resistance-capacitance oscillators, and phase-locked loops with embedded voltage-controlled oscillators used for clock generation and management and for high-speed serializer-deserializer (SERDES) transmit clocks and receiver clock recovery. Fairly common are differential comparators on input pins designed to be connected to differential signaling channels. A few "mixed signal FPGAs" have integrated peripheral analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) with analog signal conditioning blocks allowing them to operate as a system-on-a-chip . Such devices blur the line between an FPGA, which carries digital ones and zeros on its internal programmable interconnect fabric, and field-programmable analog array (FPAA), which carries analog values on its internal programmable interconnect fabric.
The FPGA industry sprouted from programmable read-only memory (PROM) and programmable logic devices (PLDs). PROMs and PLDs both had the option of being programmed in batches in a factory or in the field (field-programmable). However, programmable logic was hard-wired between logic gates.
In the late 1980s, the Naval Surface Warfare Center funded an experiment proposed by Steve Casselman to develop a computer that would implement 600,000 reprogrammable gates. Casselman was successful and a patent related to the system was issued in 1992.
Some of the industry's foundational concepts and technologies for programmable logic arrays , gates, and logic blocks are founded in patents awarded to David W. Page and LuVerne R. Peterson in 1985.
The 1990s were an explosive period of time for FPGAs, both in sophistication and the volume of production. In the early 1990s, FPGAs were primarily used in telecommunications and networking. By the end of the decade, FPGAs found their way into consumer, automotive, and industrial applications.
21ST CENTURY DEVELOPMENTS
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A recent trend has been to take the coarse-grained architectural
approach a step further by combining the logic blocks and
interconnects of traditional FPGAs with embedded microprocessors and
related peripherals to form a complete "system on a programmable
chip". This work mirrors the architecture created by Ron Perlof and
Hana Potash of Burroughs Advanced Systems Group in 1982 which combined
a reconfigurable CPU architecture on a single chip called the SB24.
Examples of such hybrid technologies can be found in the Xilinx
Zynq-7000 All Programmable SoC, which includes a 1.0 GHz dual-core ARM
Cortex-A9 MPCore processor embedded within the FPGA's logic fabric or
An alternate approach to using hard-macro processors is to make use of soft processor cores that are implemented within the FPGA logic. Nios II , MicroBlaze and Mico32 are examples of popular softcore processors. Many modern FPGAs are programmed at "run time", and this is leading to the idea of reconfigurable computing or reconfigurable systems – CPUs that reconfigure themselves to suit the task at hand. Additionally, new, non-FPGA architectures are beginning to emerge. Software-configurable microprocessors such as the Stretch S5000 adopt a hybrid approach by providing an array of processor cores and FPGA-like programmable cores on the same chip.
Companies like Microsoft have started to use FPGA to accelerate high-performance, computationally intensive systems (like the data centers that operate their Bing search engine), due to the performance per Watt advantage FPGAs deliver.
* 1982: 8192 gates, Burroughs Advances Systems Group, integrated
into the S-Type 24-bit processor for reprogrammable I/O.
* 1987: 9,000 gates,
* 1985: First commercial FPGA :
* 2005: 80,000 * 2008: 90,000
Historically, FPGAs have been slower, less energy efficient and
generally achieved less functionality than their fixed ASIC
counterparts. An older study had shown that designs implemented on
FPGAs need on average 40 times as much area, draw 12 times as much
dynamic power, and run at one third the speed of corresponding ASIC
implementations. More recently, FPGAs such as the
Advantages of FPGAs include the ability to re-program in the field to fix bugs, and may include a shorter time to market and lower non-recurring engineering costs. Vendors can also take a middle road by developing their hardware on ordinary FPGAs, but manufacture their final version as an ASIC so that it can no longer be modified after the design has been committed.
* Integrated circuit development costs are rising aggressively * ASIC complexity has lengthened development time * R white-space:nowrap;">. Customers wanting a higher guarantee of tamper resistance can use write-once, Antifuse FPGAs from vendors such as Microsemi .
In 2012, researchers, Sergei Skorobogatov and Christopher Woods, demonstrated that FPGA's can be vulnerable to hostile intent. They discovered a critical backdoor vulnerability had been manufactured in silicon as part of the Actel/ Microsemi ProAsic 3 making it vulnerable on many levels such as reprogramming crypto and access keys, accessing unencrypted bitstream, modifying low-level silicon features, and extracting configuration data.
An FPGA can be used to solve any problem which is computable . This
is trivially proven by the fact FPGA can be used to implement a soft
microprocessor , such as the
Specific applications of FPGAs include digital signal processing , software-defined radio , ASIC prototyping, medical imaging , computer vision , speech recognition , cryptography , bioinformatics , computer hardware emulation , radio astronomy , metal detection and a growing range of other areas.
FPGAs originally began as competitors to CPLDs and competed in a similar space, that of glue logic for PCBs . As their size, capabilities, and speed increased, they began to take over larger and larger functions to the point where some are now marketed as full systems on chips (SoC ). Particularly with the introduction of dedicated multipliers into FPGA architectures in the late 1990s, applications which had traditionally been the sole reserve of DSPs began to incorporate FPGAs instead.
Another trend on the usage of FPGAs is hardware acceleration, where one can use the FPGA to accelerate certain parts of an algorithm and share part of the computation between the FPGA and a generic processor.
Traditionally, FPGAs have been reserved for specific vertical applications where the volume of production is small. For these low-volume applications, the premium that companies pay in hardware costs per unit for a programmable chip is more affordable than the development resources spent on creating an ASIC for a low-volume application. Today, new cost and performance dynamics have broadened the range of viable applications.
Common FPGA Applications:
* Aerospace and Defense
* Avionics/ DO-254 * Communications * Missiles & Munitions * Secure Solutions * Space
* Medical Electronics * ASIC Prototyping
* Connectivity Solutions * Portable Electronics * Radio * Digital Signal Processing (DSP)
* High Resolution Video * Image Processing * Vehicle Networking and Connectivity * Automotive Infotainment
* Real-Time Video Engine * EdgeQAM * Encoders * Displays * Switches and Routers
* Consumer Electronics
* Digital Displays * Digital Cameras * Multi-function Printers * Portable Electronics * Set-top Boxes * Flash Cartridges
* Servers * Security * Hardware security module * Routers * Switches * Gateways * Load Balancing
* High Performance Computing
* Servers * Super Computers * SIGINT Systems * High-end RADARs * High-end Beam Forming Systems * Data Mining Systems
* Industrial Imaging * Industrial Networking * Motor Control
* Scientific Instruments
* Lock-in amplifiers * Boxcar averagers * Phase-locked loops
* Industrial Imaging * Secure Solutions * Hardware security module * Image Processing
* Video "> Simplified example illustration of a logic cell
The most common FPGA architecture consists of an array of logic blocks (called configurable logic block, CLB, or logic array block, LAB, depending on vendor), I/O pads, and routing channels. Generally, all the routing channels have the same width (number of wires). Multiple I/O pads may fit into the height of one row or the width of one column in the array.
An application circuit must be mapped into an FPGA with adequate resources. While the number of CLBs/LABs and I/Os required is easily determined from the design, the number of routing tracks needed may vary considerably even among designs with the same amount of logic. For example, a crossbar switch requires much more routing than a systolic array with the same gate count. Since unused routing tracks increase the cost (and decrease the performance) of the part without providing any benefit, FPGA manufacturers try to provide just enough tracks so that most designs that will fit in terms of lookup tables (LUTs) and I/Os can be routed. This is determined by estimates such as those derived from Rent\'s rule or by experiments with existing designs.
In general, a logic block (CLB or LAB) consists of a few logical cells (called ALM, LE, slice etc.). A typical cell consists of a 4-input LUT, a full adder (FA) and a D-type flip-flop , as shown below. The LUTs are in this figure split into two 3-input LUTs. In _normal mode_ those are combined into a 4-input LUT through the left mux . In _arithmetic_ mode, their outputs are fed to the FA. The selection of mode is programmed into the middle multiplexer. The output can be either synchronous or asynchronous, depending on the programming of the mux to the right, in the figure example. In practice, entire or parts of the FA are put as functions into the LUTs in order to save space.
Modern FPGA families expand upon the above capabilities to include higher level functionality fixed into the silicon. Having these common functions embedded into the silicon reduces the area required and gives those functions increased speed compared to building them from primitives. Examples of these include multipliers, generic DSP blocks, embedded processors, high speed I/O logic and embedded memories.
Higher-end FPGAs can contain high speed multi-gigabit transceivers
and _hard IP cores_ such as processor cores,
Most of the circuitry built inside of an FPGA is synchronous circuitry that requires a clock signal. FPGAs contain dedicated global and regional routing networks for clock and reset so they can be delivered with minimal skew . Also, FPGAs generally contain analog PLL and/or DLL components to synthesize new clock frequencies as well as attenuate jitter . Complex designs can use multiple clocks with different frequency and phase relationships, each forming separate clock domains. These clock signals can be generated locally by an oscillator or they can be recovered from a high speed serial data stream. Care must be taken when building clock domain crossing circuitry to avoid metastability. FPGAs generally contain block RAMs that are capable of working as dual port RAMs with different clocks, aiding in the construction of building FIFOs and dual port buffers that connect differing clock domains.
To shrink the size and power consumption of FPGAs, vendors such as
Xilinx's approach stacks several (three or four) active FPGA die side-by-side on a silicon interposer – a single piece of silicon that carries passive interconnect. The multi-die construction also allows different parts of the FPGA to be created with different process technologies, as the process requirements are different between the FPGA fabric itself and the very high speed 28 Gbit/s serial transceivers. An FPGA built in this way is called a _heterogeneous FPGA_.
Altera's heterogeneous approach involves using a single monolithic FPGA die and connecting other die/technologies to the FPGA using Intel's embedded multi-die interconnect bridge (EMIB) technology.
DESIGN AND PROGRAMMING
To define the behavior of the FPGA, the user provides a design in a hardware description language (HDL) or as a schematic design. The HDL form is more suited to work with large structures because it's possible to just specify them numerically rather than having to draw every piece by hand. However, schematic entry can allow for easier visualisation of a design.
Then, using an electronic design automation tool, a technology-mapped netlist is generated. The netlist can then be fit to the actual FPGA architecture using a process called place-and-route , usually performed by the FPGA company's proprietary place-and-route software. The user will validate the map, place and route results via timing analysis , simulation , and other verification methodologies. Once the design and validation process is complete, the binary file generated (also using the FPGA company's proprietary software) is used to (re)configure the FPGA. This file is transferred to the FPGA/ CPLD via a serial interface (JTAG ) or to an external memory device like an E EPROM .
The most common HDLs are
Verilog , although in an attempt to
reduce the complexity of designing in HDLs, which have been compared
to the equivalent of assembly languages , there are moves to raise the
abstraction level through the introduction of alternative languages .
To simplify the design of complex systems in FPGAs, there exist libraries of predefined complex functions and circuits that have been tested and optimized to speed up the design process. These predefined circuits are commonly called _IP cores _, and are available from FPGA vendors and third-party IP suppliers (rarely free, and typically released under proprietary licenses). Other predefined circuits are available from developer communities such as OpenCores (typically released under free and open source licenses such as the GPL , BSD or similar license), and other sources.
In a typical design flow, an FPGA application developer will simulate the design at multiple stages throughout the design process. Initially the RTL description in VHDL or Verilog is simulated by creating test benches to simulate the system and observe results. Then, after the synthesis engine has mapped the design to a netlist, the netlist is translated to a gate level description where simulation is repeated to confirm the synthesis proceeded without errors. Finally the design is laid out in the FPGA at which point propagation delays can be added and the simulation run again with these values back-annotated onto the netlist.
More recently, OpenCL is being used by programmers to take advantage of the performance and power efficiencies that FPGAs provide. OpenCL allows programmers to develop code in the C programming language and target FPGA functions as OpenCL kernels using OpenCL constructs.
B ASIC PROCESS TECHNOLOGY TYPES
* SRAM – based on static memory technology. In-system programmable
and re-programmable. Requires external boot devices.
By 2006, long-time industry rivals
Other manufacturers include:
Lattice Semiconductor (SRAM based with integrated configuration
flash, instant-on, low power, live reconfiguration)
In March 2010, Tabula announced their FPGA technology that uses time-multiplexed logic and interconnect that claims potential cost savings for high-density applications. On March 24, 2015, Tabula officially shut down.
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* FPGA Center, tutorials