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Linley Newsletter

ARM CPU Secures APM Processor

June 20, 2011

Author: Joseph Byrne

At the Linley Tech Carrier Conference on June 6, 2011, AppliedMicro provided additional details about the trust-management unit in its PacketPro line and about the company’s newly announced PacketPro APM86791 processor. This PowerPC product is a lower-cost derivative of the PacketPro family targeting low-end routers and access points; the first of these processors are nearing qualification for production.

The trust-management unit is part of PacketPro’s SlimPro subsystem. Residing at the heart of SlimPro is a 250MHz CPU, which AppliedMicro recently revealed to be an ARM Cortex-M3. Able to boot from an on-chip ROM, which is inherently trustworthy, SlimPro endows PacketPro with unusually high integrity. The ROM-based program can load a larger kernel image from off chip, cryptographically authenticate this code, and jump to it for a second boot stage. This second stage locks in a configuration for the overall PacketPro processor; it then loads and authenticates the boot code for the primary PowerPC CPUs and turns over control to those CPUs. The result is a system that is hard to hack, as any change to the PowerPC software causes authentication to fail.

SlimPro can also authenticate code during run time. The system passes an image from DRAM to SlimPro, which compares a hash of this image with a known-good hash to ensure that the copy in DRAM has not been altered. SlimPro can also hold cryptographic keys for PacketPro’s security accelerator.

The newest PacketPro model to incorporate SlimPro is the APM86791 Keelback, a cost-reduced version of previously announced Mamba and Diamondback processors. Compared with earlier PacketPros, it offers only a single CPU that tops out at 1.0GHz. For further cost reduction, AppliedMicro packages the chip in a 19mm wire-bonded BGA instead of a 27mm flip-chip BGA. Other features include various hardware engines to accelerate packet processing, four Gigabit Ethernet controllers, and two controllers each for PCI Express Gen2 ×1, SATA, and USB. AppliedMicro plans to sample Keelback in 3Q11 and qualify it for production in 1Q12. The company has not disclosed pricing, but we estimate that it will be less than $20 in 1,000-unit quantities.

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