Low-Power Computing For Embedded Mobile System Software With DVS Support

With rapid development of semiconductor technologies, embedded circuit technology has been improved constantly. The integration and complexity of the chip is increased, as well the size is getting smaller and smaller. As the performance of processor increased, the power consumption of processor is bigger than ever before. Because of the improved integration and complexity, the power consumption is rising. Power consumption per unit area is rising linearly as circuit area increase. The rising of power consumption per unit becomes a constraint for processor development. Most of the mobile embedded systems are driven by battery. Because of the limitation of battery capacity, mobile embedded systems should be more power aware. Compared to the rapid development of processor technology, battery technology is lag behind. So extending the limited battery life is one of the important topics for portable embedded systems.Embedded system is a mixture of hardware and software. Power is consumed by hardware running. Software is the controller of hardware, and it drives the hardware to run. So software is the sole of embedded system, and it is consuming power by driving the hardware run indirectly. For power aware computing, the behavior and characteristic of software should be taking into account. Especially, the DVS technology provides an effective way for software to reduce the hardware power consumption. By the help of DVS, software can adjust the core supply voltage of processor dynamically.In this thesis, it focuses on applying DVS to mobile embedded system. There are some questions about using DVS in mobile embedded system. One question is what about the battery behavior will be affected by DVS, and the other is what about the effective of using DVS in real-time embedded system. So this thesis makes the following contributions:(1)First, it presents a battery driven power aware design method for mobile embedded system with DVS support. The discharged capacity of battery is not a constant, which will be affected by current intensity. And the current of battery is decided by hardware running status. So in this thesis, the relationship between battery capacity discharged and DVS is studied. Then this thesis gives a power aware mobile embedded system design method driven by battery. This method quantifies the DVS impact on battery capacity, and gives a theory model about power aware design. According to this model, it deduces a principle for mobile embedded system power aware design.(2)It proposes a power aware operating system scheduling and a power aware dispatching for storage devices access requests, especially for real-time system. It first studies the real-time task model with DVS support, and use offline schedule to try completing the tasks as much as possible during the battery life with the task deadline guaranteed. As the offline schedule is static, and it can't gain any running information. Operating system could collect the running information for whole system or any tasks. On this basis, an online schedule algorithm is developed to enhance the offline scheduler. Power consumption for peripheral equipments is also very important. This thesis takes HDD as an example, to study the power reduction technology for HDD using access requests schedule.(3) This thesis also studies how to use compiler to support lower power scheduling. The compiler is used to analyze the memory behavior of task, and build a task power model. Using this model, compiler gives a static DVS decision for task. And it also studies the cooperative protocol between Operating system and Compiler. Operating system uses the fine-grained information from compiler static decision in power aware task scheduling. This fine grained information would give some hint for online schedule.At last, this thesis evaluates the proposed power aware method and optimization. Experimental results show that these optimization methods can effectively reduce the power consumption for whole system. This research fully utilizes the characteristics of DVS technology and battery. It studies DVS technology effective for low power real-time scheduling and compilers from battery model, and gives a system level solution.