Hindawi Publishing Corporation International Journal of Reconfigurable Computing Volume 2010, Article ID 570279, 10 pages doi:10.1155/2010/570279 Review Article Reconfigurable Multiprocessor Systems: A Review Taho Dorta, Jaime Jimenez,´ Jose´ Luis Martın,´ Unai Bidarte, and Armando Astarloa Department of Electronics and Telecommunications, University of the Basque Country, UPV/EHU, 48013 Bilbao, Spain Correspondence should be addressed to Taho Dorta, [email protected] Received 28 February 2010; Revised 31 July 2010; Accepted 26 October 2010 Academic Editor: Viktor K. Prasanna Copyright © 2010 Taho Dorta et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Modern digital systems demand increasing electronic resources, so the multiprocessor platforms are a suitable solution for them. This approach provides better results in terms of area, speed, and power consumption compared to traditional uniprocessor digital systems. Reconfigurable multiprocessor systems are a particular type of embedded system, implemented using reconfigurable hardware. This paper presents a review of this emerging research area. A number of state-of-the-art systems published in this field are presented and classified. Design methods and challenges are also discussed. Advances in FPGA technology are leading to more powerful systems in terms of processing and flexibility. Flexibility is one of the strong points of this kind of system, and multiprocessor systems can even be reconfigured at run time, allowing hardware to be adjusted to the demands of the application. 1. Introduction significantly. Figure 1 shows the number of publications in the Inspec database using “multiprocessor” and “FPGA” as Multiprocessor Systems-on-Chip (MPSoC) represent an search keywords. important trend in digital embedded electronic systems. Reconfigurable Multiprocessor Systems, also known as MPSoC are systems-on-chip with more than one processor. Multiprocessor-on-Programmable Chip (MPoPC) (or Soft New applications in modern embedded systems require Multiprocessor), are normally presented as a way of making complex multiprocessor designs to reach Real-Time (RT) prototype systems for subsequent implementation on an deadlines while overcoming other critical constraints such as ASIC. Now, not only prototypes are implemented using power consumption and low area. MPSoC seem to be the FPGAs, but final designs too. The growth in FPGA capacity solution for such complex systems. A lot of applications such allows designers to implement a complete multiprocessor as networking, multimedia, and control benefit from this system in a single FPGA. The main FPGA companies offer type of system. The perfect example of this is a cell phone. the possibility of using softcore processors specially designed Currentmodelsmustoffer low power consumption and to fit well in the FPGA; also, some FPGAs allow the use integrate a large number of functions such as audio and video of hard-core processors. Furthermore, FPGAs are equipped encoding, image processing, and Internet access. MPSoC with on-chip memory blocks, peripherals, and interconnec- offer better performance with lower energy consumption tion circuitry. Run-time reconfigurability is one of the strong in this kind of complex systems compared to uniprocessor points of FPGA-based multiprocessors systems. This feature embedded systems. Traditionally, the trend in uniprocessor allows multiprocessor systems to be adapted to a particular systems was to improve performance by increasing clock application, gaining flexibility in the designed system. frequency; now the trend is to work in parallel with lower In the following section, we discuss the viability of frequencies, in order to reduce energy consumption [1–3]. FPGA-based Multiprocessors. In Section 3,weprovidesome In the field of MPSoC, the reconfigurable or FPGA- examples of FPGA-based multiprocessors implemented by based multiprocessor is a new and increasingly important the research community in recent years. In Section 4,we trend. It facilitates rapid prototyping and allows research into examine the challenges of MPoPC. After that, a number of new architectures and communications techniques without different methods of design are presented. In the final section the problems of MPSoC ASIC production. The number of this paper, we highlight a number of important aspects of papers published over the last three years has increased relating to MPoPCs. 2 International Journal of Reconfigurable Computing 2. Viability of FPGA-Based Multiprocessor 90 80 Systems 80 77 The first question we must ask is whether there is any 70 66 sense in implementing a multiprocessor system on an FPGA. The answer is that it depends. The main disadvantage of 60 51 this kind of multiprocessor is reduced performance com- 50 pared with ASIC multiprocessor systems. However, FPGA- Multiprocessor systems have a number of advantages that 40 compensate for this in some way. Publications 30 27 19 20 17 16 (i) Flexibility and reconfiguration. The number of softcore 13 14 processors that can be included is limited only by the capacity 10 of the FPGA. Also, it is possible to configure each processor independently adding cache, FPU modules, and so forth. 0 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 (year) (ii) Less time-to-market. The design process does not include the manufacture of the IC, with a considerable reduction in Figure 1: FPGA multiprocessor publications trend (2010 Febru- design time. ary). (iii) Less cost. The process is cheaper. Nowadays a state-of- the-art FPGA is relatively cheap, enabling own design with 3. FPGA-Based Multiprocessor Systems a small work team. Furthermore, if there is an error in the system design, this is not decisive. In this section, we describe several multiprocessor systems implemented in FPGA. We have tried to include systems ff (iv) Scalability. FPGA-based multiprocessors systems can that represent the di erent trends in architecture and appli- house an increasing number of microprocessors or periph- cations. First, we provide a little background information erals if there are logic resources available in the FPGA. about MPSoC and FPGA-based multiprocessor systems. Therefore, using FPGA is the best choice in certain cases. We also present the most widely accepted classification of MPSoCs: homogeneous and heterogeneous. Multiprocessor (i) Low-volume, mission-critical designs (e.g., radar and systems can be also classified as shared-memory systems military applications). or distributed-memory systems. We also highlight recent advances in run-time reconfigurable multiprocessor systems (ii) Rapid design of new, reconfigurable multiprocessor and give examples of these systems. systems. (iii) Research field. New architectures, memory hierar- 3.1. Main FPGA-Based Processors. In FPGA-based multipro- chies, interprocessor communication, and so forth, cessor systems, the most widely used FPGA soft processors can be developed. are made by one of the two main FPGA companies: Xilinx (iv) Naturally-grown systems. Systems that have to be or Altera. The other option is to use open-source soft able to grow in features depending on the stage of processors. development [4]. Xilinx is the most widely used brand in MPoPC systems. It supplies three main processors: softcore MicroBlaze (MB), The use of FPGA technology provides numerous benefits PicoBlaze (8 bits reduced soft processor), and hard-core for the design of embedded systems. These benefits include PowerPC. The number of PowerPcs is limited by the FPGA the ability to fix design bugs in the FPGA hardware, model to a maximum of four. The number of MicroBlaze and upgrade a system in the field, or simply swap out hardware PicoBlaze processors is limited only by logic resources. functionality without redesigning the physical board that The MicroBlaze is a 32-bit RISC softcore processor. It contains the FPGA [5]. FPGAs already provide a compelling uses the Harvard memory architecture, that is, it has a sepa- time-to-market advantage over ASICs, and advanced tools rate instruction memory and data memory. The MicroBlaze targeting the needs of high-end FPGA designers would help can issue a new instruction every cycle, maintaining single- establish clear leadership [6]. cycle throughput under most circumstances. The shared-bus Ravindran et al. discuss the viability of soft multipro- solution is the CoreConnect On-Chip Peripheral Bus (OPB), cessors [7, 8]. According to them, it is necessary to answer and every MicroBlaze has Fast Simplex Link (FSL) ports to these two questions: (a) Can soft multiprocessors achieve make efficient point-to-point connections [9]. performance levels competitive with custom multiprocessor PicoBlaze is based on an 8-bit RISC architecture and can solutions? (b) How do we design efficient systems of soft reach speeds of up to 100 MIPS in Virtex-4 family FPGAs. multiprocessors for a target application? In both papers, they The processors have an 8-bit address and data port for demonstrate the viability of soft multiprocessors. access to a wide range of peripherals. The core license allows International Journal of Reconfigurable Computing 3 Table 1: Main FPGA processor models. to combine these: master-slave with pipeline, for instance, is very common. Processor Company Type Bits Comments (1) In master-slave systems, one or more processors act MicroBlaze Xilinx RISC 32 bits Harvard as the master processor,