Limits of Conventional STA
STA, while very successful, has a number of limitations:
- Cannot easily handle within-die correlation, especially if spatial correlation is included.
- Needs many corners to handle all possible cases.
- If there are significant random variations, then in order to be conservative at all times, it is too pessimistic to result in competitive products.
- Changes to address various correlation problems, such as CPPR (Common Path Pessimism Removal) make the basic algorithm slower than linear time, or non-incremental, or both.
SSTA attacks these limitations more or less directly. First, SSTA uses sensitivities to find correlations among delays. Then it uses these correlations when computing how to add statistical distributions of delays.
Interestingly, there is no technical reason why determistic STA could not be enhanced to handle correlation and sensitivities, by keeping a vector of sensitivities with each value as SSTA does. Historically, this seemed like a big burden to add to STA, whereas it was clear it was needed for SSTA, so no-one complained. See some of the criticism of SSTA below where this alternative is proposed.
Read more about this topic: Statistical Static Timing Analysis
Famous quotes containing the words limits of, limits and/or conventional:
“In a virtuous action, I properly am; in a virtuous act, I add to the world; I plant into deserts conquered from Chaos and Nothing, and see the darkness receding on the limits of the horizon.”
—Ralph Waldo Emerson (1803–1882)
“An art whose limits depend on a moving image, mass audience, and industrial production is bound to differ from an art whose limits depend on language, a limited audience, and individual creation. In short, the filmed novel, in spite of certain resemblances, will inevitably become a different artistic entity from the novel on which it is based.”
—George Bluestone, U.S. educator, critic. “The Limits of the Novel and the Limits of the Film,” Novels Into Film, Johns Hopkins Press (1957)
“First it must be known that only a spoken word or a conventional sign is an equivocal or univocal term; therefore a mental content or concept is, strictly speaking, neither equivocal nor univocal.”
—William of Occam (c. 1285–1349)