Actel, ARM put soft CPU in FPGA -

Actel, ARM put soft CPU in FPGA


FREMONT, Calif. — Actel Corp. and ARM Ltd. will announce Monday (March 7) a collaboration that has led to the first certified ARM CPU core available as soft IP for implementation in an FPGA.

Previously, Altera had released an FPGA with a diffused ARM processor on the die, but this is the first time such a core has been available as soft IP.

Three barriers had to be overcome to make the product possible, according to the partners: size and performance, license issues and the challenge of protecting ARM's intellectual property from theft.

Until recently, FPGAs lacked the density and performance to implement a full ARM-compliant processor core in the logic fabric. At current densities, this is no longer the case. “All but three or four of the smallest FPGAs in Actel's ProASIC-3 family can do useful SoC designs that include the ARM core,” said Wayne Lyons, ARM's director of embedded solutions.

Even so, the two companies found it necessary to collaborate on a special implementation of the core optimized for use in the FPGA. “This is an ARM7 tdmi-s core, without a cache controller or MMU,” Lyons explained. “We determined that many of today's embedded applications are running at no more than 40 MHz, and don't use these features.”

Dennis Kish, Actel vice president of marketing, added that even with the high underlying performance of the Pro-ASIC flash-based FPGA fabric, “The core will require a significant amount of circuit optimization. This is going on as we speak.”

While these measures will put the ARM core in the size and performance range for many embedded applications, that leaves two more issues to be addressed: licensing and security.

The licensing problem will be handled by a novel exploitation of the fact that the Actel FPGAs include an encryption engine on-chip to handle encrypted programming bit streams. Actel will release a new version of the ProASIC-3 family that will be labeled as “ARM-Enabled.”

These devices will have a modified bit stream decoder that will recognize and accept the specially-encrypted bit stream for the ARM core. The license fee for using the ARM architecture will be bundled in the price of the FPGA chips, making access to a soft ARM license available for the first time to customers whose needs are too small to justify a license directly with ARM.

“This is bringing ARM to the masses without making them buy a stand-alone CPU chip,” Kish said.

The encryption approach also deals with the security issue. Because the ARM core is supplied in an encrypted form, and can only be successfully encoded into an ARM-enabled ProASIC-3, there is little chance of the IP being hijacked, according to the companies.

“This was a big issue for ARM,” Lyons said. In fact, it could be a big issue for both companies in the hot Asian market, as it for the first time will make an ARM license available to small SoC developers there. These companies had previously relied on ARM-based microcontroller chips.

The devices, for which final pricing has not yet been set, will be handled by a standard ARM co-marketing approach: ARM will promote the devices in its target application areas, but the chips will be sold directly by Actel.

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