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Embedded Systems October 2000 Vol13_11

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devices such as Web processors, car navigation systems, and other new-age consumer-e lectroni cs devices be ing suggested by Internet designe rs. The approach rests on two bedrock concepts, according to the two compa- nies. First, there is Lx's new clustered VLIW core architecture (see Figure 1) and microarchi tecture specialized to an application domai n that ensures scaleabili ty and customizability. Next, HP and ST have developed a toolchain they say is based on "aggres- sive ILP technology." This is intended to give the user a uniform view of the platform at th e programming lan- guage level. The first maj ol' peek at the Lx pro- j ect came in June, when engineers from the two companies delivered a j oint paper on the effort at the 27th Annual In te rnational Symposium on Computer Architecture in Vancouver, B.C. In terms of design, the basic Lx is laid out as a cluster of four VLIW exe- cution units. That is, the low-end design would be a four-issue machine con ta ining four 32-bit integer ALUs, two 16-by-32 multipliers, one load/ store unit and one branch unit. One level up in the family, an eight- issue device could be constructed by ganging together two clusters. The added cluster would bring along its own set of registers, along with other detritus to minimize the difficulties inhe rent in scaling up a processor. Lx also relies on a two-level code compression scheme. The instruction cache is compressed so that unused slots don 't consume space durin g encoding, the compani es' engineers write. More ambitious is an effort in the works to compress binaries with Huffman-Ii ke tech n iq ues and then decompress blocks of instructions dur- ing I-cache retil ls. To clarify each company's role in the overall effort, so far as is known publicly, HP developed the insu'uction set architecture and much of the soft- ware behind Lx, while ST implement- ed the hardware. "The Lx proj ect has concentrated on producing a highly automated way o f explo ring architectures," said Shephe rd . "Not on implemen ting them, but exploring them." Though Shephe rd 's statemen t sounds cryptic, he really means that the process is not yet enti rely hands off. Right now, the tools output a com- piled description of the device that must be tweaked. However, he sees things moving in the direction of even- tual full automation. In a separate effort that delves in to some of the same concepts as Lx, HP is also working on a proj ect called tlle PICa Architecture Synthesis System. (PICa itself stands for "Program In , Chip Out"). Led by Bob Rau, out of HP's labs in Cupertino, CA, PICa also aims to create a set of software tools that could make it economically feasi- ble to quickly roll custom processors in low volumes for specialized embed- ded applications. Howevel~ PICa appears to be work- ing with more complex cores, akin to HP and Intel's highly advanced lA-54 architecture. Lx takes a more down- sized tack, both in terms of power con- sumption and complexity. esp Optimizing C Compiler Integrated Development Environment Built-in Macro Assembler BClink Linker Runs under: Windows 95/9 Also available for DOS, HP-UX Alfxandfr Wolfe is fdi tor-at-largf for ESP. He holds a BE in eli' ftrical engi- neering from Coo/Jer Unio ll. Hp has writ- ten assembly language code f or embedded systems. He is co-author of From Chi ps to Sys tems: An In t roduction to Microcompute rs, 2nd Edition (Sybex, 1987). He can be reached at awol[e@C1/ljJ .I'O'/1/ x40 j S&Ox20) table() ; LIMITaD Resources Faraboschl p. G. Brown. et al. "Lx: A Technology Platform for Customizable VlIW Embedded Processing." IS avail- able at www.hpl.hp.comlcambridge/ projeds/cfpldocsllSCAOO paper. pdf 114 oaOBER 2000 Embedded Systems Programming

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