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FPGA FAQ

14/09/2021, hardwarebee

What is FPGA and why it is used?

 

FPGA stands for Field Programmable Gate Array. It’s a programmable integrated circuit, a chip that can be programmed unlimited times and perform any digital function i.e., mathematical equations, state machines, implement signal processing algorithms and more.

 

FPGA would be able to perform any digital logic operation. In FPGAs, there are small blocks named Look-up-Tables (LUT), all the functions, codes, logic we wish to implement is synthesized into these LUTs to mimic the operations of that logic. All the logic is converted into Boolean equations and these equations are implemented in the LUTs to behave exactly as the RTL code.

 

So, FPGA is a programmable chip that is designed to implement any function in the form of digital logic that are implemented into the LUTs.

 

What is FPGA programming used for?

 

FPGA programming is being used to program the FPGA chip. The programming language is usually calls RTL which has the two main flavors: Verilog and VHDL. A developer can write a program in any one of these languages, the program is then downloaded into the FPGA. FPGA programming can be used for implementing various designs such as signal processing, communication interfaces, image processing, logic operations, and protocol implementation.

 

FPGA programming depicts the hardware functionality. VHDL syntax is more like Pascal  language while Verilog is similar to C, which is more user friendly. There is no limitation to what a digital design can be used with a any of these programing languages.

 

Is FPGA faster than GPU?

 

This question has been discussed so many times, and there is an enormous amount of data available to support both devices trying to beat each other. Generally, it is not straightforward to give the answer to this question and announce the verdict in the favor of one.

 

The hardware architecture of FPGA and GPU are quite different, FPGAs are based on LUT and they are generic so the developer can program it or use them accordingly, whereas GPU has series of cores where a thread-level distributor, distribute the load to many cores to achieve high performance.

 

It all depends on the application and the developers ability to use the resources optimally and tailored to the application. For example, image and computer vision applications will perform faster on GPU based on vector processing rather than FPGA, but FPGA will perform faster for communication protocol implementation where parallel processing can be exploited easily.

 


Is FPGA faster than CPU?

 

For parallel processing, FPGA is faster than a CPU. FPGA logic can work and manipulate things in a parallel fashion rather than sequential fashion. CPU is based on instruction set architecture, each vendor like Intel or AMD has its architecture and instruction set. These instructions are running on the ALU in a sequential fashion. Each instruction has a different number of clock cycles to execute instructions. Whereas in FPGA, LUTs are operating in parallel to perform a task. A CPU is more generic and can perform any task, while an FPGA has a programmable hardware architecture that enables parallel processing capabilities and be used, for example, in high-speed applications.

 

CPUs are sequential devices that process instructions in series order. Whereas FPGAs are parallel processing devices, this allows completing an entire process in single clock cycle. In FPGAs, multiple parallel execution units can be built, to allow distribution of the implementation across several blocks.

 

What are the advantages of FPGA?

 

FPGA advantages are: re-programmability, flexibly, parallel processing, low development cost, fast time to market,  In addition to that, they have a simple design cycle, a design can set up the entire development environment within a few hours. FPGAs are also suitable for real-time data processing, the allow code manipulation and code updating is very easy and flexible.

 

Various vendors offer IP cores that are available for fast prototyping, for example different communication peripheral block such as SPI, ethernet and more.

 

What language is used for FPGA?

 

VHDL, Verilog and System Verilog are the most common languages.

 

FPGA is programmed using Hardware Description Languages such as Verilog and VHDL. These languages are used to program FPGAs since the 1980s. To use these languages the programmer needs to think at low hardware level, such as gates, flip flops and multiplexers.

 

Verilog and VHDL are used to write the application at a higher abstraction level that depicts the functional and behavioral level. Then these codes are converted into the netlist through software conversion tools.

 

How many times can you reprogram an FPGA?

 

Tens of Thousands, sometimes as long as the FPGA is intact, you can still program it.

 

FPGA vendors like Altera and Xilinx do not specify how many times one can program an FPGA. These devices are based on SRAM technology — SRAM is a set of transistors one can use as long as they didn’t burn out.

 

So, you can program FPGAs tens of thousands of times. FPGA device configuration is volatile. As power goes down the configuration goes down. The programmer can load the program again and again. Xilinx and Altera never set a limitation or neither published how many times one can load and unload the configuration.

 

Can FPGA replace CPU?

 

Absolutely yes, but it depends on the size of the CPU and it’s functionality. Today, designers can get a CPU IP core and download it into an FPGA. There is also a possibility to add an operating system into the FPGA. In this case the user can even develop the software and add additional hardware around the CPU to support additional functionality.

In recent years, FPGA vendors have introduced a new type of FPGAs that are very similar to SoC (System on Chip) architecture. This means that a CPU is almost always one of the blocks inside the FPGA.

 


Why are FPGA expensive?

 

FPGAs are expensive as there are very few vendors who manufactured FPGA chips – the market is not competitive enough. Also, it requires a huge amount of research and development effort and capital to design and produce FPGAs in high volume.

 

Developing an FPGA requires a set of complex software tools that are also provided by the FPGA vendors. Developing and updating these tools requires also time and money that is added to the FPGA cost.

 

Why is ASIC faster than FPGA?

 

FPGA’s architecture is based on many logic gates and a flexible connectivity matrix. This flexibly increase internal delay therefore has impact on speed. ASIC is particularly designed to implement a specific function without any redundant logic that exist in an FPGA. Therefore, FPGA is better for ASIC prototyping, and ASIC is a better fit to high volume production applications. In ASIC design an engineer designs the logic, power lines and clocks according to the application, whereas in the FPGA all resources are present and the engineer can use them automatically through programming.

 

Because ASICs are optimized for one specific application and can be realized on more advanced semiconductor manufacturing process node than FPGAs, as a result ASIC circuits can run at a much higher speed than FPGAs.

 

What are the disadvantages of FPGA?

 

FPGA chips are relatively expensive to manufacture, which make then unattractive for high volume applications. In many case, FPGAs are ending up being used as prototypes. FPGA’s flexibility makes them slow in speed compared to a dedicated ASIC. FPGA also consume more power than ASIC which makes them less energy-efficient and more power-hungry.

 

In addition to that, FPGAs cannot include analogue blocks, therefore, the only use of an FPGA is for implementing digital logic circuits.

 

Why FPGA prefer over microcontroller?

 

FPGA can be given preference over microcontrollers, as microcontrollers are not effective to handle a huge amount of data, they have memory constraints and they also base on the instruction set architecture, so they depend on the instruction cycle time that makes them slow. It is preferable to use FPGA compared to the microcontroller.

 

How do I start an FPGA developer?

 

The first step is to learn digital design, know how the processor works, have some basic programming fundamentals. Then you can start learning VHDL/Verilog, FPGA architecture, , learn about FPGA design tools. Later on you can, practice your skills with using or modifying some FPGA free codes, then you will be able to write code for FPGA yourself.

 


What is FPGA design?

 

FPGA design flow starts with specifications, RTL coding, then synthesis that converts the design into the netlist, use an FPGA tool like Vivaldo to do the mapping, where the logic goes into the FPGA which LUTs should use to implement the logic, then after that you need to perform placement and routing, after that, a bit file will be generated that the user can download onto the FPGA.

 

What is the difference between CPLD and FPGA?

 

CPLD is the subset of FPGA. FPGA has a large logic density than a CPLD. CPLDs are based on the PAL and PLA architecture, and FPGA is based on LUTs architecture. CPLDs have a fixed placement and routing structure whereas FPGAs have versatility in placement and routing. From for programming perspective, both can program as many times as they can, CPLDs have a better power consumption compare to FPGAs. FPGAs are larger in size while CPLD are smaller in size.. FPGA can operate in higher speed than CPLDs. FPGA are more expensive than CPLDs.

 

What are field-programmable gate arrays used for?

 

FPGA are great in applications that require flexibly and re-programmability. For example, in cases where the functionality of the FPGA would need an update after product deployment. FPGA has a fast time to market, and offer high performance, a simple design cycle, and suitable for real-time data processing.

 

FPGAs are particularly good for prototyping purposes. Because an FPGA can be reprogrammed millions of times engineers use FPGA to debug and create a bug-free code. FPGA can be used for prototyping for new chips before design ASIC or send them foundry for the final chip manufacturing.

 

What are FPGAs good for?

 

FPGAs are good for applications that require flexibly and reprogrammability. Today, FPGA are used for various application such as: parallel application processing, communication systems and video processing algorithm. FPGA can easily meet power requirements, size, cost, and security challenges for all different kinds of applications.

FPGAs are particularly good for prototyping specific applications or processors. An FPGA can be reprogrammed millions of times until the design is final and bug-free, this is particularly beneficial for ASIC prototyping.

 

What are the most common uses for FPGA today?

 

FPGAs are being used in a wide range of applications such as in medical equipment, communication hardware, and radio devices. Following are some more applications of the FPGAs.

 

  • Data centers
  • Radar signal processing
  • Communication
  • Protocol implementation
  • Image and Video processing
  • Machine learning
  • Neural Network
  • Aerospace and defense
  • Telecom and data

 

How do I start a simple FPGA design?

 

The first step is to learn the digital logic design, get some basic programming fundamentals, acquire knowledge about FPGA design tools and flow. Then you can start learning about VHDL/Verilog, get familiar with FPGA architecture, practice some easy FPGA codes, then you will be able to write your own code for FPGAs. Good luck. Oh yes, and you can always check out our FPGA Academy.

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