VLIW processors: once blue sky, now commonplace

摘要

Very long instruction word (VLIW) is an architectural style that one of the authors-Josh Fisher- proposed about 30 years ago to speed up computers and otherwise enhance their performance. Those listening to Fisher's first public "blue-sky" expositions of this technology [1] in the early 1980s did not generally expect it to succeed. Indeed, they would have been stunned to hear of the success these processors are enjoying today, especially as embedded processors, designed to perform special-purpose functions, usually in real time, in some kind of hardware. For example, the VLIW family we are most familiar with, the STMicroelectronics ST200 [2], accounts for more than 70 million processor cores in just the past few years. VLIW processors are beginning to dominate the most performance-intensive embedded applications, including everyday consumer-level electronics found in Best Buy, FNAC, or the Akihabara district: mobile phones, digital televisions, receivers and recorders, digital cameras, multifunction printer/scanner/copier/faxes, and more. VLIWs obtain high performance from ordinary programs in a way that is simple to describe: Instead of issuing a single operation from an instruction stream in a given cycle, a VLIW processor issues many of them together in a single execution stream, and it issues new operations before old ones have finished.