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Boosting Battery Life For RISC Processors
prostoalex writes "National Semiconductor and ARM Holdings will jointly develop the power management solution for RISC chips, that they estimate will improve battery life by 25-400%. The target date of the first sample product is Q2 2003." My old Tadpole laptop sure could have used this. I counted myself as lucky when I got a whole 45 minutes out of a battery.
When developing portable devices the most limiting factor today is not processing resources, memory or anything such. It is simply the power source.
Batteries of today are either too weak or too heavy. How ofter does one have to choose between a slim-line battery or an ultra-long life.
There have been many suggestions for competing technologies such as fuelcells, harvesting of motion energy and solar cells to mention a few. But still, they have proven to be too expensive, large or have some other problem (such as not being ready for production use yet). Hopefully these one of these, or any other, portable power sources will make it possible to carry real computing power without having to carry a heavy battery pack.
The solution today is to reduce the power usage. This can be done by shutting down parts of the clock trees in the CPUs, or by using Intel's PowerStep (i.e. two working speeds), or Transmetas's variable voltage and frequency technology, LongRun. As the article lacks technical details we can only guess about the techniques used behind the PowerWise solution. Also, the figures 25-75% efficiency gain is most probably measured under special conditions.
But, in order to avoid sounding too negative, it seems like the industry has realized the problem and are working for a solution. I feel that most of today's solutions (power saving) are just a cure for the symptoms (bad battery time), not for the cause (bad battery technology).
Another advantage of the ARM is the Thumb instructions that reduces the traffic over the memory bus. We must remember that driving memory bus is an expensive operation (power wise) compared to finding data in the cache. Smaller code means more code in the cache. One problem is that multimedia applications (such as movies, music, etc) fails to utilize the cache well (since the data isn't re-accessed). This is a problem area that needs more research.