Software benefits of FPGA

Question

I have a doubt: I understood that it takes advantage of hardware parallelism and that it controls I/O at the hardware level in order to provide faster response times but which are the software benefits of an FPGA? Which software components can be accelerated? Thanks in advance.

Answer 1

Some think of FPGAs as an alternative to processors. This is usually fundamentally wrong. FPGAs are customizable logic. You can implement a processor in a FPGA and then run your regular software on that processor. The key advantage with FPGAs is the flexibility to implement any kind of logic.

Think of a processor system. It might have a serial port, USB, Ethernet. What if you need another more specialized interface which your processor system does not support? You would need to change your hardware. Possibly create a new ASIC.

With a FPGA you can implement a new interface without the need for new hardware or ASICs.

FPGAs are almost never used to replace a processor. The FPGA is used for particular tasks, such as implementing a communications interface, speed up a specific operation, switch high bandwidth communication traffic, or things like that. You still run your software on a CPU.

Answer 2

You are correct about the parallelism and I/O control of an FPGA. FPGA's are just huge re-configurable logic circuits that allow a developer to create circuits with very specific and dedicated functions. They typically come with a very large amount of I/O when compared to typical micro-controllers as well. Because it is basically a bunch of gates in silicon, everything you code in your hardware description language (HDL) will happen in parallel. This combined with the fact that you can write custom circuits is what gives the ability to accelerate operations in an FPGA over a typical processor even though the processor may have a much higher clock speed. To better illustrate this point, lets say you have an algorithm that you need to run and you want to compare an FPGA to a processor. The FPGA is clocked at 100Mhz and the processor at 3Ghz. This means the processor is running at a rate that is 30 times faster than the FPGA. Let's say you code up a circuit that is capable of computing the algorithm on the FPGA in 10 clock cycles. The equivalent algorithm on a processor could take thousands of instructions to execute. This places the FPGA far ahead of the processor in terms of performance. And, because of the parallel nature of FPGA's, if you code it right and the flow through the FPGA is continuous, every clock cycle, the FPGA can finish the computation of a new result. This is because every stage in an FPGA will execute concurrently. So it may take 10 clock cycles, but at each clock cycle, a different piece of 10 different results can be computed simultaneously (this is called pipelinine: http://en.wikipedia.org/wiki/Pipeline_%28computing%29 ). The processor is not capable of this and can not compute the different stages in parallel without taking extra time to do so. Processors are also bound on a performance level by their instruction set whereas on an FPGA, this can be overcome by good and application specific circuit design. A processor is a very general design that can run any combination of instructions, so it takes longer to compute things because of its generalized nature. FPGAs also don't have the issues of moving things in and out of cache or RAM. They typically do use RAM, but in a parallel nature that does not inhibit or bottleneck the flow of the processing. It is also interesting to note that a processor can be created and implemented on an FPGA because you can implement the circuits that compose a processor.

Typically, you find FPGAs on board with processors or microcontrollers to speed up very math intensive or Digital Signal Processing (DSP) tasks, or tasks that require a large flow of data. For example, a wireless modem that communicates via RF will have to do quite a bit of DSP to pick signals out of the air and decode them. Something like the receiver chip in a cell phone. There will be lots of data continually flowing in and out of the device. This is perfect for an FPGA because it can process such a large amount of data and in parallel. The FPGA can then pass the decoded data off to a microcontroller to allow it to do things like display the text from a text message on a pretty touchscreen display. Note that the chip in your cell phone is not an FPGA, but an ASIC (application specific integrated circuit). This is a bunch of circuits stripped down to the bare minimum for maximum performance and minimal cost. However, it is easy to prototype ASICs on FPGAs and they are very similar. An FPGA can be wasteful because it can have a lot of resources on board that are not needed. Generally you only move from an FPGA to an ASIC if you are going to be producing a TON of them and you know they work perfectly and will only ever have to do exactly what they currently do. Cell phone transceiver chips are perfect for this. They sell millions and millions of them and they only have to do that one thing their entire life.

On something like a desktop processor, it is common to see the term "hardware accleration". This generally means that an FPGA or ASIC is on board to speed up certain operations. A lot of times this means that an ASIC (probably on the die of the processor) is included to do anything such as floating point math, encryption, hashing, signal processing, string processing, etc. This allows the processor to more efficiently process data by offloading certain operations that are known to be difficult and time consuming for a processor. The circuit on the die, ASIC, or FPGA can do the computation in parallel as the processor does something else, then gets the answer back. So the speed up can be very large because the processor is not bogged down with the computation, and is freed up to continue processing other things while the other circuit performs the operation.

Answer 3

Both for prototyping and parallelism. Since FPGAs are cheap they are good candidates for using both when making industrial protypes and paralell systems. FPGAs consist of arrays of logic elements connected with wires. The elements contain small lookup tables and flip-flops. FPGAs scale to thousands of lookup tables. Lookup tables and programmable wires are flexible enough to implement any logic function. Once you have the function ready then you might want to use ASIC. Xilinx and Altera are the major brands. Personally I use the Altera DE2 and DE2-115.