Finding Fusion
Actel's Single-Chip Savant

In assembling a typical embedded system, we often find ourselves on our system-design podium, conducting a virtual symphony of suppliers – analog components companies for the wiggly parts of our system, MCU/CPU suppliers handing us processing capabilities, ASIC companies for high-performance custom hardware, and FPGA companies providing glue logic to help connect the incompatible parts we’re using from all the other suppliers. Any time we can increase our level of integration and reduce the number of suppliers and components, we save ourselves design time, BOM cost, power, and form-factor space. If we can integrate and add programmability, we also reduce our risk, further shorten our design cycles, and increase the life of our system in the field. Since we can distribute new software (or firmware) and hardware just by sending out a new bitstream for a programmable system-on-chip device, our customers can upgrade, add features, and get bug fixes after our systems have shipped. We can also develop a single physical hardware platform that can be reconfigured as many different product variants serving different points in the market by leveraging programmability.

Actel announced this week that it has begun shipping its new Fusion programmable system-on-chip devices. The combination of features Fusion brings to the table sets a new standard for single-chip diversity for integration of embedded systems. Normally, we digitally-biased embedded systems designers consider only part of the picture in our quest for integration. We are all too happy to defer the analog part of our design to the tie-dye wearing types down the hall. They can have their own chips so none of that messy stuff spills over onto our silicon. Of course, we understand that our final product includes lots of things outside the boundaries of our “system-on-chip” efforts. Mechanical parts, power supplies, antennae, and other components congregate around our centerpiece device, brining data and signals in and out and connecting us to the physical world. It’s all too easy to let analog slide onto the other side of a dividing line in our system-level gerrymandering.

Actel’s Fusion family is a programmable system device, probably closest to an FPGA with built-in analog. Fusion’s built-in analog allows us to integrate much more of our system into a soft-hardware reprogrammable device. We can have analog, ARM7 processors, memory, peripherals, interconnect busses, and custom hardware modules all contained in a single device that can be reprogrammed in the field. It challenges our usual definitions and requires us to re-think our regular design strategy, considering new possibilities. In order to ease that transition, Fusion also carries with it a well-conceived design environment and methodology that will simplify the task of assembling a single-chip, mixed-signal embedded system-on-chip with built-in volatile and non-volatile memory.

Image provided by Actel.

Fusion was born of marketing savvy and a fortuitous combination of features in Actel’s existing Pro-ASIC FPGA technology. Actel took advantage of the higher voltages and other characteristics of its flash-based ProASIC FPGA architecture to add analog capabilities that would be difficult to adapt from any other starting point. The wider voltage rails required for flash also allow greater swing and accuracy in analog components of the device and simplify analog connectivity to the outside world by eliminating the need for voltage scaling. Actel’s triple-well process also reduces noise in analog portions of the circuit, creating isolation from the switching noise of the digital domain.

Image provided by Actel.

Actel’s Fusion concept goes a great distance beyond a new FPGA family with a little added analog. While the new family boasts a unique combination of programmable fabric, volatile and non-volatile memory, soft and external processor integration and programmable analog, it also comes complete with a multi-tiered design philosophy that will offer embedded system design teams a simple, mix-and-match, IP-based design flow. Actel’s Fusion design philosophy is based on a layered scheme of plug-and-play IP, which Actel calls a “Fusion Technology Stack”.

At the lowest level of the architecture, which Actel calls “Level 0”, are “Fusion peripherals” which are IP blocks ranging from hard-wired IP to programmable analog blocks to soft-programmed blocks. These peripherals can be selected from a library of Actel and third-party provided IP, or created by the user. Connecting these components together is the “Fusion Backbone” (“Level 1” for those following along in our diagram) which is an intelligent bus structure capable of managing peripheral configuration and controlling peripheral behavior via a low-level state machine integrated into the backbone.

One level up from the Fusion Backbone, is Level 2, the “Fusion Applet”. An applet is a higher-level building block implementing a function based on programmable hardware fabric, and communicating with peripherals through the backbone. Actel has designed the applet structure as the primary IP integration level, with a well-defined interface for plug-and-play use of IP from a variety of sources. The robustness of this level of Actel’s environment, the degree of complexity involved with integrating new IP applets into the Fusion framework, and ultimately Actel’s success in providing a rich library of applets through original development and third-party partnerships is likely to be a key deciding factor in Fusion’s success in the market.

Sitting atop the Applet layer, at Level 3 are what Actel refers to as “System Applications”. These applications are generally user-supplied and are built in reprogrammable logic fabric from groups of applets working together. Actel claims that System Applications allow complete Fusion-based systems to be created without any HDL coding. Dispensing with the HDL requirement opens up the new Fusion platform to a much wider audience, and brings single-chip system design within reach of the masses of embedded system design teams who might have previous experience only with board-based systems.

Leveraging their recently announced partnership with ARM, Actel offers an ARM7 soft-core processor in Fusion along with its existing 8051 microcontroller. The Fusion architecture is designed to be compatible with external processors/MCUs as well, giving design teams the flexibility to choose a processing environment that best suits the needs of their design. The combination of the IP-based hardware configuration environment and industry-standard processors and programming environments opens up Fusion to a broader and more diverse audience.

Fusion devices are available in sizes ranging from 90K to 1.5M “system gates” (Note to the uninitiated: these are not to be confused with any gates you studied in school. Conventional wisdom is that you should divide by a factor of 4 to 10 to compare with a conventional standard like ASIC gates) They contain integrated block RAM ranging from 6 to 60 blocks at 512X9 per block, yielding from 27K to 270K bits of RAM. They also contain 1K flash ROM blocks and from 256KB to 1,024KB of embedded flash that can be used for non-volatile storage of encryption keys, subscriber info, serial numbers and other data required for many of today’s popular embedded device services.

In the new analog area, the devices contain from 5 to 10 analog quads, and from 15 to 30 analog inputs plus from 5 to 10 FET drivers. For total I/O, this means (depending on package and device selection) that Fusion devices range from 53 digital with 20 analog I/O to 228 digital with 40 analog I/O.

Image provided by Actel.

Actel says initial target applications for Fusion include power and temperature management applications like smart battery charging, fan and heat-element control and monitoring, and other voltage, current and temperature monitors and alarms. Fusion would also be appropriate for motor and motion control, system initialization and configuration, and virtually any application requiring a tightly integrated digital and analog system with non-volatile storage, low-power consumption, and high performance.

Actel is now shipping Fusion silicon samples (with volume prices starting at $4.95 (USD) per device in the second half of 2006), software design tools, and a starter kit with software, evaluation board, tutorial and documentation, programmer, and debugger for $349 (USD). Fusion likely leads a wave of new, highly integrated programmable devices that will be hitting the embedded systems market over the next few years. Expect to see devices with more specific IP built-in aimed at highly targeted applications, but including both digital and analog programmability so that systems designers can add their own value to their end products.

Kevin Morris, Embedded Technology Journal

December 13, 2005

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