ARM Wrestles picoTurbo in Court By Tom R. Halfhill PicoTurbo, a two-year-old startup based in Milpitas, Calif., has a new twist on ARM: a family of embedded-processor cores that's compatible with the ARM architecture. Indeed, the cores are apparently too compatible for ARM, which has filed a patent-infringement lawsuit against picoTurbo in U.S. District Court in San Jose. ARM alleges that picoTurbo infringes three of ARM's U.S. patents. One patent describes shadow registers that temporarily store the contents of data registers during exception processing. The other two patents are related to ARM's Thumb instructions -- a subset of the normal 32-bit instruction set that uses 16-bit instruction words for greater code density. PicoTurbo maintains that its cores do not infringe on ARM's patents, because they either don't perform the patented functions or perform similar functions in different ways, with an independently designed "clean room" microarchitecture. PicoTurbo's pT-100, pT-110, and pT-120 cores are based on a similar design with several variations. Like the ARM9, they are 32-bit uniscalar RISC processors with five-stage pipelines and fully static cores. To address different segments of the market, picoTurbo removed some elements from the pT-110 to produce the lower-end pT-100, and it added some features to produce the higher-end pT-120. But even the pT-100 retains a 32-bit Wallace-tree multiplier, a separate Thumb decoder, a 32-bit barrel shifter, and power-management logic. It's easy to see why ARM is giving picoTurbo the cold shoulder. Millions of dollars are at stake for both companies. ARM feels compelled to defend its hard-won market share against an invader that is undercutting its license fees and royalties. PicoTurbo stands to gain a lucrative chunk of the market by riding the coattails of the popular ARM architecture. We don't expect this case to be settled anytime soon.