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Roundtable: Will the mcu-fpga combination remain a high end solution?

Roundtable: will the mcu-fpga combination remain a high end solution?

In the late 1990s, a leading fpga company launched a campaign under the heading of 'system on a programmable chip'. The idea was that the combination of a programmable logic fabric and a soft processor would help to cut time to market and reduce development costs. For a number of reasons, the idea didn't catch on quite as anticipated.

Since then, the concept of an fpga replacing microcontroller functionality in industrial products has surfaced every so often, but the approach hasn't found any particular interest. However, attention is turning again to the idea. Altera, for example, has recently unveiled its SoC FPGA concept, while Xilinx has launched the Zynq platform. Both approaches blend hard ARM processor systems with a programmable fabric and both have the industrial market in their sights.

So will this version of a programmable device appeal to the industrial market? What are the benefits and, importantly, what are the drawbacks? New Electronics discussed the issues at a recent roundtable.

According to a recent survey, 57% of mcu based products designed by New Electronics readers feature an fpga. Of these, 70% have considered moving mcu functionality into an fpga. So, if the interest is there, what's stopping them?

Steve Clark, director of Arrow Design Solutions, pointed out the 8bit sector remains the largest part of the microcontroller market. "There are thousands of customers developing products based on 8bit mcus," he said. "Demand remains strong because these companies care about cost and low power." The inference is the fpga based approach just doesn't meet these needs.

But are things beginning to change? "Not necessarily," said Clark. "We're seeing an unprecedented choice of new mcus. The ARM architecture has opened up the market." Because vendors now have to differentiate on peripherals, more capable mcu solutions are available to designers.

And Clark outlined other reasons why designers may be happier to stay with mcus. "One reason is price; fpgas are expensive and we have never won a design on price alone. Another reason is competition; designers only see a limited number of fpga vendors, but a wide range of mcu vendors. They see the fpga route as narrowing their choice," he contended.

Stefano Zammatio, product manager with Altera Europe, said: "Semiconductor vendors have increased the number of mcu variants. How do you know what's going to be the best solution? Adding an fpga to your design might add more cost, but it's a way to differentiate."

But while demand for 8bit mcus remains strong, there are other sectors of the market. And that is where the fpga vendors are beginning to look. Giles Peckham, Xilinx' European marketing director, said: "While 8bit is a commodity market, 16bit and 32bit mcus are where designers are more likely to add their own functionality." Clark commented: "16 and 32bit mcus tend to be used in IP based applications – security and point of sale systems, for example. Those applications could be good targets for fpga based designs."

Zammatio believes there's a good reason why low end mcu sales remain high. "You wouldn't design a mechanical control system today; it's too hard. It's easier to use an 8bit mcu and there is a trail of low end applications where 'good enough' is 'good enough'." He also believes applications evolve. "Basic control might suit an 8bit mcu, but integration means you might need to move up in technology. The trend is to more features, smaller, cheaper and this won't go away."

Why have Altera and Xilinx decided now is the time to address the industrial market? Zammatio said: "Altera and Xilinx have offered hard processors for 10 years, but these haven't dominated because they were targeted at fpga customers and the combination of a high cost fpga and a high cost processor didn't have much appeal. Now, power consumption is lower, cost is lower and the approach is more competitive with high end mcus."

Peckham added: "Zynq is different to what Xilinx offered before because it's a processor, not an fpga. Alongside the ARM cores, there's a programmable fabric; you can extend the I/O through high speed connectivity and can accelerate routines. It's an SoC that looks like a processor and that allows software engineers to 'own' the project."

Zammatio outlined the advantages of the fpga based approach. "While standard products bring the lowest power and cost, you can only differentiate via software. FPGAs allow you to integrate the system; not just putting an mcu and an fpga together, but also bringing in other functions.

"Designers can then add custom features and change them. They can migrate designs to a new fpga to reduce cost while bringing in new hardware features. FPGAs are an easier way to move IP to a lower cost platform and you don't have to wait for a vendor to upgrade an assp.

Zammatio gave motor control as an example of this progression. "A decade ago, it was an mcu/dsp. As you look for more control, you need encoders and a/d conversion; communications needs an Ethernet chip; handling a display probably needs a system processor. Then there's custom PWM control and so on. Suddenly, the original chip is looking inadequate.

"The solution is to integrate the components into an fpga. It has an ARM processor and standard peripherals that allow a powerful motor control system to be developed. All custom features are in soft logic and the developer has full control of the system."

For Xilinx, Peckham noted the suitability of the Zynq processor to similar applications. "It includes everything needed for it to be treated as a processor. It's flexible, even though it's hard programmable." But he admits Zynq is not necessarily a cheaper solution. "But when you look at the cost of ownership, it becomes more attractive. When customers take a look at the bigger picture, they see more value in Zynq.

"People gradually warmed to the idea of mcus in fpgas the past, but take up not what was expected. With Zynq, it's surprising how many more people see value. It's not for everyone, but we're surprised at the response."

The New Electronics survey also picked up concerns about design tools. Peckham admitted Zynq had a new design flow, but said that, in the long term, the move would bring flexibility. "And users can access the ecosystem you'd expect for a standard ARM processor."

Zammatio added: "Altera's Quartus software allows someone to create a custom mcu based system. Today, someone who isn't a hardware designer can design hardware systems. And we're looking to introduce OpenCL into the design flow."

Concluding, Clark said: "The availability of more capable fpga based solutions is moving engineers away from the 'pick and mix' approach. FPGAs allow them to take a system view; not only what can be done today, but also what can be done in the future. But it's about what the customer wants to achieve. If there's a mix of products, then flexibility and inventory costs become more important."

Graham Pitcher

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