| Designing Software Radio Systems With FPGAs |
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| Sep 01 2008 | |
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advertisement: While these DSP capabilities of new FPGAs are truly remarkable, several other significant features add even more benefits to software radio applications. Onboard serial gigabit transceivers and channel coding/decoding engines support the emerging switched serial fabric protocols that are quickly replacing conventional parallel buses and backplanes for high speed inter-chip and interboard data transfers. Other new features include onboard programmable RISC processors that can execute code for local supervision and control functions, thus greatly reducing the need for an external host processor. These processors slash loop latencies to deliver much tighter real-time control systems. Ethernet MACs (media access controllers), incorporated as I/O resources for the latest generation FPGAs, simplify TCP/IP communication links to a wide range of host processors and various operating systems. Finally, complete switched fabric engines supporting protocols such as PCI Express save valuable FPGA resources for other signal processing tasks. Evolution of New FPGA FeaturesFPGA vendors constantly strive to outdo their competition in an exciting race to provide features that deliver maximum performance and specific benefits. Winning this race, however, is a complex and elusive goal. Many different types of resources are now found in FPGAs including block RAM, distributed RAM, DSP blocks, logic blocks, microcontrollers, gigabit ports, I/O drivers and pins. Trying to find a single optimum ratio of resources is futile because each application requires a different mix. For example, the design engineer selecting the best part for a logic-intensive application will avoid an FPGA device heavily burdened in cost and power with a wealth of powerful DSP blocks. As a compromise, vendors have developed multi-pronged product offerings, each targeting different classes of applications.After the Virtex-II Pro family, Xilinx began using this strategy with the Virtex- 4 family, splitting the devices into three sub-families, each emphasizing distinct application spaces. In its latest Virtex-5 family, Xilinx now offers four distinct sub-families, each with its own special blend of resources. Devices within three of these four sub- families have been released so far. The Virtex-5 LX devices provide an ample quantity of logic slices but offer no gigabit serial interfaces. The LXT and SXT devices add the gigabit serial interfaces, along with PCI Express fabric end-point engines to simplify system connectivity. Like the LX and FX families in the Virtex-4 family, the Virtex-5 LXT and SXT devices offer maximum resources for logic and digital signal processing algorithms, respectively. The yet unreleased FXT devices should follow suit with the Virtex-4 FX devices by providing 405 PowerPC processor cores and other resources well suited for embedded systems. The chart in Figure 1 summarizes the highlights of the evolving resources in three successive generations of Xilinx FPGAs. |
