24-12-2009, 07:30 PM
Abstract
In January of 2000, Transmeta Corporation introduced the Crusoe processors, an x86- compatible family of solutions that combines strong performance with remarkably low power consumption. As might be expected, a new technology for designing and implementing microprocessors underlies the development of these products. As might not be expected, the new technology is fundamentally software-based: the power savings come from replacing large numbers of transistors with software.
The Crusoe processor solutions consist of a hardware engine logically surrounded by a software layer. The engine is a very long instruction word (VLIW) CPU capable of executing up to four operations in each clock cycle. The VLIWâ„¢s native instruction set bears no resemblance to the x86 instruction set; it has been designed purely for fast lowpower implementation using conventional CMOS fabrication. The surrounding software layer gives x86 programs the impression that they are running on x86 hardware. The software layer is called Code Morphing software because it dynamically morphs x86 instructions into VLIW instructions. The Code Morphing software includes a number of advanced features to achieve good system-level performance. Code Morphing support facilities are also built into the underlying CPUs. In other words, the Transmeta designers have judiciously rendered some functions in hardware and some in software, according to the product design goals and constraints. Transmetaâ„¢s Code Morphing technology changes the entire approach to designing microprocessors. By demonstrating that practical microprocessors can be implemented as hardware-software hybrids, Transmeta has dramatically expanded the design space that microprocessor designers can explore for optimum solutions. Upgrades to the software portion of a microprocessor can be rolled out independently from the chip. Finally, decoupling the hardware design from the system and application software that use it frees hardware designers to evolve and eventually replace their designs without perturbing legacy software.
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