| Designing Software Radio Systems With FPGAs |
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| Sep 01 2008 | |
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advertisement: Putting FPGAs To WorkTaking advantage of these resources for a high-performance software radio product illustrates the usefulness of the sub-family differentiation. Shown in Figure 2 is the Model 7142 PMC (PCI Mezzanine Card) module suitable for use in many different types of embedded software radio systems, including PCI, VME, and CompactPCI card cages. The XMC extension to PMC defined by VITA 42 offers gigabit serial links supporting the new popular switched fabric protocols. Four 125 MHz 14-bit A/D converters and one 500 MHz 16-bit D/A converter provide analog IF (intermediate frequency) signal interfaces to external analog RF up and down converters and RF amplifiers for ultimate connection to the antenna. Real-time digital signal processing tasks such as digital up and down conversion, modulation and demodulation, encoding and decoding, and other operations are often all performed using FPGA-based DSP resources. All PMC modules require a PCIbus interface. However, if the interface is equipped with DMA controllers and FIFO buffers, they can dramatically improve performance by initiating efficient data transfers between the PCI bus and the many peripherals on the module. To qualify as an XMC module, the unit must include gigabit serial transceivers and some facility for implementing a serial fabric and/or protocol.Commencing just before the availability of Virtex-5 devices, the design cycle of this product dictated the use of the Virtex- 4 family. The only Virtex-4 sub-family that met all of the requirements was the versatile FX series, so it became an obvious choice for this product. Nevertheless, the FX family is quite limited in DSP capability compared to the SX family. Even the largest member of the FX family has only the same number of XtremeDSP slices as one of the smaller SX devices. Since customer access to ample DSP horsepower was a critical factor, an SX55 device was added to the PMC module, significantly boosting the total quantity of DSP slices from 192 to 704. After incorporating the SX55 to handle real-time digital signal processing for the A/D, D/A, and SDRAM, those peripherals were attached directly to it by choosing the most appropriate interface type. Therefore, the FX device became the natural candidate for the PCI interface, DMA controller, and giga-bit serial interface. To speed development time and ensure full compatibility with all PCI 2.2 PCIbus specifications, the PCI interface for the FX device incorporated an off-the-shelf IP core. Because of the many different peripherals and devices, the local side of the PCI core is supported with a custom 9-channel DMA engine and FIFO buffers. This provides a dedicated logical channel to and from the PCI bus to manage multiple streams and simplify transfers. |
