Method and Apparatus for Power Management in a Multi-voltage System
Original Publication Date: 2002-May-08
Included in the Prior Art Database: 2003-Jun-21
Mobile PC systems' operations are severely limited by battery technology. The power used by the system's microprocessor keeps increasing due to gains in technology that enable additional function and faster operational speed. However, battery technology doesn't realize gains as fast paced as semiconductor technology. In addition, the space constraints dealt with in the design of mobile PCs limits the battery size. Since the size of a battery is directly related to its physical volume, this places an upper limit to the amount of power a battery can supply to a system, hence the length of operation while operating on battery. This problem was recognized after the first round of mobile PC systems were introduced. A person could not travel by plane from New York to L.A. and work continuously with their mobile system without carrying multiple spare batteries. There have been several attempts in both the mobile PC system and the operating system to reduce the power requirements. With the exception of completely turning off devices and components within the PC, which is not always practical, all efforts to extend the useful life of a battery have been towards mechanisms that save power based upon a linear relationship. This invention describes the software and states required to save power based upon the inverse square law. This is a major advantage over power saving techniques in practice today. Mobile PC Systems in general are very similar to the ubiquitous desktop PC. Most of this is required because of software compatibility reasons. This presents an interesting dilemma to the mobile PC Manufacturer. A mobile PC is required to have a lot of the same logic and devices as a desktop, but it doesn't have the same power supply capacity when it is receives power from a battery. Operation of the mobile PC while powered by an electric utility is virtually unlimited, devices and logic may remain powered on all the time and the microprocessor can run at its maximum specified clock rating. This presents some interesting challenges when mobile PC users are travelling for long distances and don't readily have convenient access to an electric utility power source. To work around the battery life constraints, most mobile PC systems employ some form of power management. It may be all in the hardware or it may be a combination of both hardware and software. Managing power only in the hardware is awkward and if done, may lead to using more power and affecting the reliability of certain hardware components. For example, the mobile PC could turn off the hardfile when it is not busy. The problem here is that the hardware has no idea when the next request will arrive. The hardfile actually consumes more power if it is powered-off and then instantaneously powered-on as the start-up current is very high compared to leaving the hardfile on once the media is up to speed.