FPGA computing systems: A Bird’s Eye View

Nowadays the complexity of computing systems is skyrocketing. Programmers have to deal with extremely powerful computing systems that take time and considerable skills to be instructed to perform at their best. It is clear that it is not feasible to rely on human intervention to tune a system: conditions change frequently, rapidly, and unpredictably. It would be desirable to have the system automatically adapt to the mutating environment. This module analyzes the stated problem, embraces a radically new approach, and it introduces how software and hardware systems ca ben adjusted during execution. By doing this, we are going to introduce the Field Programmable Gate Arrays (FPGA) technologies and how they can be (re)configured.

Traditionally, computing was classified into General-Purpose Computing performed by a General-Purpose Processor (GPP) and Application-Specific Computing performed by an Application-Specific Integrated Circuit (ASIC). As a trade-off between the two extreme characteristics of GPP and ASIC, reconfigurable computing has combined the advantages of both. On one hand reconfigurable computing can have better performance with respect to a software implementation but paying this in terms of time to implement. On the other hand a reconfigurable device can be used to design a system without requiring the same design time and complexity compared to a full custom solution but being beaten in terms of performance. The main advantage of a reconfigurable system is its high flexibility, while its main disadvantage is the lack of a standard computing model. In this module we are presenting a first definition of reconfigurable computing, describing the rationale behind it and introducing how this field has been influenced by the introduction of the FPGAs.

From the mid-1980s, reconfigurable computing has become a popular field due to the FPGA technology progress. An FPGA is a semiconductor device containing programmable logic components and programmable interconnects but no instruction fetch at run time, that is, FPGAs do not have a program counter. In most FPGAs, the logic components can be programmed to duplicate the functionality of basic logic gates or functional Intellectual Properties (IPs). FPGAs also include memory elements composed of simple flip-flops or more complex blocks of memories. Hence, FPGA has made possible the dynamic execution and configuration of both hardware and software on a single chip. This module provides a detailed description of FPGA technologies starting from a general description down to the discussion on the low-level configuration details of these devices, to the bitstream composition and the description of the configuration registers.