Optimization of power consumption for an ARM7-based multimedia handheld device

We have developed a multimedia handheld educational device and optimized the current consumption not only by employing several software optimization techniques but also by using dynamic clock frequency scaling scheme (DFS). Although the ARM7 CPU employed does not support operating voltage scaling, the controlling of the operating frequency helps reducing the current consumption in the idle time and results in up to 25 % of power reduction in the system level. The CPU operation frequency is determined by profiling the multimedia program components, which include LZW (Lempel-Ziv Welch) image decompression, MP3 audio decoding, CELP based speech decoding, speech recognition and ADPCM. Especially, it is shown that the time for LZW decompression is proportional to the image size rather than the size of the compressed file. The CPU load becomes almost full, between 80 to 95%, after applying the DFS.