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Communications breakdown

16 сентября 2008

Freescale Semiconductor invented the communications processor more than 15 years ago, and its PowerQuicc products have become hugely popular for a wide variety of networking and communications functions. Intel and other vendors offer similar products combining general- purpose CPUs with programmable data-plane engines.

But the era of the communications processor is winding down as designers increasingly turn to multicore processors to perform these functions. These processors can run the control plane on one CPU and the data plane on additional CPUs. Despite the performance and power inefficiencies of this approach, designers appreciate the simpler programming model.

Freescale is fighting back with a line of multicore processors under its new QorIQ brand. But the company faces much more competition in the multicore space.

Technology trends

Several trends have led to the downfall of the communications processor. The initial PowerQuicc chips handled many common protocols, such as TDM, HDLC and Fast Ethernet, using their data-plane engine, known as the CPM. New protocols could be added with only a firmware upgrade; PowerQuicc was able to handle almost any protocol and interwork among them.

As data rates increased, however, the CPM couldn't keep up. New chips added hard-wired MACs for Gigabit Ethernet and PCI Express. Furthermore, the rise of carrier Ethernet has reduced the need for interworking.

Applications with more complex data-plane needs, such as security and services, require a new approach. These functions require extensive software and frequent updates. OEMs often consider these functions to be their core value, therefore these functions must be programmable. Although the CPM and the newer Quicc Engine are programmable, Freescale generally does not permit its customers to program them.

Multicore concerns

Multicore processors contain general-purpose CPUs based on a popular instruction set such as Power or MIPS. These general-purpose CPUs are not particularly optimized for data-plane processing, whereas the Quicc Engine is designed specifically for these tasks. As a result, a multicore design may require more or faster CPUs to deliver the same level of performance.

As the number of CPUs exceeds four, communication and coordination among the CPUs becomes increasingly burdensome. For larger numbers of CPUs, programmers typically adopt a light OS or even a "bare metal" approach with a minimal OS.

Once this step is taken, however, the scalability of multicore solutions can be a big plus. Data-plane throughput is easily scaled by changing the number and speed of the CPUs. Cavium Networks offers versions of its Octeon processor with up to 16 CPUs, enabling a range of platforms that share hardware and software designs. Freescale, in contrast, offers the choice of one or two Quicc Engines.

According to our research, communications-processor sales peaked in 2006 at $538 million, and we expect them to drop below $150 million by 2012. During the same period, sales of multicore processors into networking and comms will rise from $52 million to more than $450 million. As chip vendors develop fewer new communications processors, system designers must consider the multicore alternative.


Источник: EETimes.com

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