Getting smarter: Three in one platform to enable platform design.

4 mins read

When the programmable logic device first appeared in the first half of the 1980s, it was used almost entirely as a means of fixing design errors – the so called 'glue logic'. But with evolutions in process technology, programmable logic has evolved.

Along the way, probably towards the end of the 1990s, programmable logic developers began talking differently about the technology. Instead of the parts being glue logic and similar, the word 'system' entered the conversation. And since then, attention has focused on the ability of a programmable logic device to absorb functionality previously provided by discrete components. However, there has been a fairly large 'but' involved in that conversation. While fpgas have been quite capable of accommodating soft processors and high speed communications links, they have, almost without exception, failed to accommodate analogue components. This apparent shortcoming was addressed by a couple of companies, again in the late 1990s, who developed programmable analogue arrays but without much success. It wasn't until 2005 that a programmable device appeared on the market which was capable of supporting logic, processor and analogue functionality. This was Fusion from Actel. Fusion blended Actel's ProASIC3 fpga fabric with support for soft microcontrollers such as ARM and 8051 and, importantly, programmable analogue components such as a/d converters and voltage and temperature monitors. At the time, Actel noted that system designers had been forced to choose discrete analogue components alongside programmable logic to implement a typical system. Fixed architectures and other technology barriers, it claimed, prevented the integration of individual components into a single chip that met all design requirements. As such, Fusion was said to be the first mixed signal fpga platform. Now Actel has moved a step on from Fusion with the launch of SmartFusion. Described by the company as 'intelligent mixed signal fpgas', the parts are being targeted at embedded designers who need an SoC solution. According to Christian Plante, director of product marketing with Actel: "SmartFusion is a convergence of three technologies in a single device. While it is a follow on device from Fusion, one of the key elements is the flash based fpga fabric. Flash allows the three elements to be combined in a single device, in turn allowing a full Cortex-M3 system to be included." The device is intended to meet many of the requirements of embedded systems developers, including the need to reduce system cost and size, as well as getting products to market more quickly. The flash based fabric helps to meet these objectives. Because it is non volatile, there is no need for sram based configuration and its voltage tolerance supports 12 to 14V on the I/Os, said Plante. "This would be difficult to do on sram based devices," he noted. Based on Actel's 130nm, seven layer metal cmos process, SmartFusion integrates a 350MHz fpga fabric with high performance programmable analogue and a hard 100MHz 32bit ARM Cortex-M3 processor. Three members of the range have been announced, with 60, 200 and 500k system gates. "When we designed SmartFusion," Plante continued, "we wanted to make sure the blocks weren't compromised. We wanted to make sure the microcontroller subsystem was the right one, with the right set of peripherals in order that it could stand alone as a microcontroller." The advantage of this, said Plante, is full customisation. "The user can partition the device as they want, bringing ease of use." Two use models are being proposed for SmartFusion based systems. The first of these targets microcontroller users who can't find the exact device they need. "In this instance," Plante suggested, "they can use the fpga fabric to provide, for example, more interfaces." The other use model is for those users who find microcontrollers either too slow for their needs or too power hungry. "Motor control needs response times of less than 1µs," Plante pointed out. "Customers tell us that getting something less than 20µs from an off the shelf device is difficult. That leaves the choice of selecting a dsp or SmartFusion. But with SmartFusion, customers have three different platforms in the one device." Security is also a growing issue with industrial designs and Actel claims to have improved this with SmartFusion. "It uses the same kind of scheme found in ProAsic fpgas," Plante explained. "This is more secure than the combination of a microcontroller and a standalone fpga. And users can specify AES encryption." At the heart of SmartFusion is an fpga fabric based on the ProASIC3 architecture. The fabric is composed of a sea of VersaTile cells, connected by four levels of routing hierarchy. Each VersaTile can implement any three input combinatorial function, a latch or a D-type flip-flop. The SmartFusion analogue solution consists of an analogue front end (AFE) and an analogue compute engine (ACE). The ACE is a small, independent processor used to offload the Cortex-M3 cpu from initialisation and control of the AFE, which comprises 12bit a/d converters running at up to 600ksample/s, sigma-delta d/a converters and system configuration blocks. The ACE is comprised of a sample sequencing engine (SSE), plus a post processing engine (PPE). The SSE sets up the a/d and d/a conversion parameters, while the PPE enables functions such as low pass filtering and linear transformation. Up to 10 50ns comparators are available, as well as up to 32 analogue inputs and three outputs. Rajiv Nema, senior product marketing manager, noted: "The ACE is equivalent in performance to an 8bit microcontroller, which can be used for pre and post processing." Nema also pointed out that SmartFusion features a full Cortex-M3 with peripherals. "It's housed in an asic cell, which is equivalent to 10million gates. If more peripherals are needed for a design, they can be created within the fpga fabric." There are a number of market segments which Actel is targeting for SmartFusion, including motor control, industrial automation and system management. In motor control applications, the device is said to allow precision control of multiple motors, with the fpga fabric implement closed loop algorithms and the Cortex-M3 handling other aspects. In industrial control, the fpga fabric is seen as being a major benefit. The programmable analogue section can handle sensing and similar tasks, while the microcontroller and the fpga fabric handle control. In system management applications, the device can monitor and control variables such as voltage, current and temperature. Software development can take place in parallel, with fpga designers using Actel's Libero suite and embedded designers working within a familiar integrated development environment. Meanwhile, the Cortex-M3's peripherals and I/O can be can be set up using the MSS Configurator. Plante said: "We've learned that we need to provide two points of access. In this way, designs can be started by embedded or by fpga designers." The Micrium rtos is supported, with more options being introduced in the near future. Initial configuration of the mixed signal portions of a design are handled via a graphical configurator included in the Libero IDE tool. At run time, C language drivers communicate with the ACE and take advantage of the analogue blocks. Unusually for announcements from the programmable logic world, SmartFusion A2F200 devices are already in volume production. Meanwhile, the A2F500 is scheduled for delivery shortly, with the A2F060 devices expected later in the year. Evaluation and development kits are also available. "We have been engaging with key customers since September 2009," Plante concluded, "and the family is already generating revenue."