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Xilinx has announced its first family of non-volatile FPGAs – the Spartan-3AN FPGA platform. Now, your first reaction may be something like: "Ho hum, just another flash-based FPGA." But there's much more to the Spartan-3AN than you might suppose.
Here's the deal. SRAM-based FPGAs typically ride the crest of the technology wave. When a new technology node arrives – such as the 65 nm node, for example – FPGAs are some of the first components to appear. This is because SRAM-based FPGAs are constructed using standard CMOS processes. Using smaller geometries allows more integration, so SRAM-based FPGAs tend to boast large amounts of on-chip RAM, multiplier cores, and so forth.
The big downside to SRAM-based FPGAs is that they are volatile – they lose their configuration when power is removed from the system &Ndash; so they require an external configuration file, which increases the number of components on the board.
By comparison, flash-based and antifuse-based FPGAs and non-volatile and do not require an external configuration device. The disadvantage to these devices is that they require additional processing steps "on top" of the standard CMOS process; the result is that they typically lag their SRAM-based cousins by one or two technology generations. For example, the two leading vendors in conventional Flash-based FPGAs are currently at the 180 nm and 130 nm technology nodes.
[Editor's Note: The various conventional FPGA fabrics are introduced and contrasted in the article FPGA Architectures from 'A' to 'Z'
In many respects, the solution introduced by Xilinx appears to offer the best of both worlds. Until now, the Spartan-3 generation of low-cost FPGAs consisted of three families: the Spartan-3 for the highest-density and pin-count applications; the logic-optimized Spartan-3E, and the I/O-optimized Spartan-3A with the largest number of I/Os and the lowest cost.
Now, Xilinx have introduced the Spartan-3AN, which essentially comprises two die stacked together in the same package. One of these die is a Spartan-3A, while the other is a flash memory from one of the world's leading vendors of flash devices (the result is pin-compatible with existing Spartan-3A platform for easy migration).
This innovative offering provides a number of advantages. First, it features one of the leading 90 nm SRAM-based FPGA fabrics. The underling Spartan-3A die boasts large amounts of block RAM and large numbers of 18 × 18 multipliers; suspend and hibernate modes providing more than 40% and 99% static power reduction, respectively; support for the 26 most popular I/O standards; and . . . the list goes on.
Meanwhile, the stacked flash device provides a huge amount of user memory. In the case of the 3S1400AN, for example, out of 16 Mbits of flash, only 5 Mbits are required for configuration, leaving 11 Mbits free for user code and applications. Furthermore, the fact that this is a state-of-the-art flash memory device means that it provides 20-year data retention and 100,000 write/erase cycles (that's up to 1,000× the write/erase cycles guaranteed by competitive offerings).
Flexible low-cost security
The Spartan-3AN platform offers a range of device security features that safeguard against reverse engineering, cloning, and unauthorized overbuilding. It builds on Xilinx Device DNA technology to provide a low-cost and effective mechanism for authenticating a valid design and ensuring a flexible design level security. Designers have full flexibility in customizing algorithms for both authentication as well as responses to authentication failures. With its embedded flash, the Spartan-3AN platform further optimizes security by hiding any configuration communication from the outside, making it extremely difficult to understand the design contained within the FPGA.
The advanced flash technology of the Spartan-3AN platform takes the DeviceDNA feature to a new level, offering factory flash ID and flash user field. The factory flash ID is very similar to the Device DNA serial number, with a unique factory set ID that is different in every flash device, offering a 64 byte long word that can be read and added into the authentication algorithm. The flash user field is a one time programmable 64 byte word that can be used to store the authentication result. The user field can also be used to store revision tracking serial numbers or user data constants that will never be changed in the system.
Next-generation configuration management
The Spartan-3AN platform provides a flexible, cost-effective approach to address the non-volatile needs of rapidly changing industries. Designers can build a single device while managing a variety of different feature sets with multiple configurations. The capacity of Spartan-3AN devices makes it possible for designers to store multiple configurations and dynamically select between configuration files.
Multiple configurations also can be used to support diagnostic nodes, feature upgrades, and complete product differentiation while using the same hardware design. Decisions such as protocols, buses, and the number of interfaces can all be dynamically changed to address new market requirements. The built-in multiboot feature, which allows virtually infinite re-configurations, lowers overall system cost and facilitates easier field upgrades.
About Spartan-3AN FPGAs
The Spartan-3AN platform is available in five non-volatile device options (3S50AN, 3S200AN, 3S400AN, 3S700AN, 3S1400AN). Configurations range from 50K to 1.4M system gates with up to 576 KB block RAM, 16 MB total embedded flash, and up to 502 I/Os supporting 26 popular I/O protocol standards, In addition, unique FPGA capabilities such as digital clock managers (DCMs), multipliers, and low power modes make these devices ideal for bridging, memory interfacing, digital signal co-processing and embedded control applications. All devices are pin-compatible with Spartan-3A FPGAs.
Pricing and availability
Customers can immediately begin designing systems with Spartan-3AN FPGAs using the ISE 9.1i design tool suite and Spartan-3 Generation library of application-specific IP. Engineering samples are shipping now for the XC3S200AN, XC3S700AN and XC3S1400AN devices with all five devices in production by Q3 2007. At customer production timeframes at the end of 2007, Spartan-3AN devices will offer designers over 4,000 logic cells and 195 I/O for USD $4.90 (250k resale volume, 3S200AN-4FT256C), resulting in the world's first integrated FPGA offering 4 Mbits of flash for under $5.00.
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