In the set-top box market, designers use DSPs need to implement fan-out connections to a Wi-Fi radio and a USB 3.0 endpoint, as shown in Figure 4.
Fig 4: Fan-out in set top box.
In this usage model, the PCIe switch is providing pure fan-out connectivity to multiple endpoints. With USB 3.0 emerging as the successor to USB 2.0 (thanks to the 10x speed bump), the trend is pointing towards more and more consumer devices incorporating this technology, thus driving up the need for PCIe connectivity.
PCIe technology has become truly ubiquitous, and the last remaining markets – DSP-based designs -- are now adopting PCIe on a large scale. These DSPs support PCIe Gen 2 for the higher speeds. However, DSPs are always going to be limited in the number of PCIe lanes and ports they can support, which often won’t be sufficient for designers. In fact, most of DSPs support only one x2 PCIe Gen 2 interface. This is where the PCIe switch comes into play; it will not only provide fan-out but also help balance the speeds and feeds in the system, due to its flexibility to operate at both Gen 1 and Gen 2 speeds on each lane or port independently.
This is tricky, however, because the markets using DSPs are varied. Some market segments need the PCIe switch to provide a large number of lanes and ports for scalability, as shown in the DSP farm usage model (figure 3) and also satisfy the “Three Ps” essential in the consumer market for designs such as set-top boxes: package, power and price.
Since the boards and systems in these markets are essentially size-limited, it is crucial for the PCIe switch come in the smallest-possible package. Power is of extreme importance in these markets – simply because these are consumer products with small board sizes and no heat-sinks and/or air-flow. It is essential that a design requires no extra components, which would drive the total system cost up, making low power all the more important.
Vendors such as PLX Technology satisfy these requirements with flexible, high-performance yet power-efficient PCIe switches, which are being designed into the full range usage models cited above. These vendors will continue to play a key role in the development of the PCIe ecosystem with the widely deployed PCIe Gen 2 standard, as well as the forthcoming PCIe Gen 3 and its 8Gbps transfer rates.
About the author:
Krishna Mallampati (email@example.com
) is product marketing director for PCIe switches at PLX Technology
, Sunnyvale, Calif.