Power Management from Linux Kernel to Android
黃俊維 R97944026 資訊網路與多媒體所 王博榮 R97942139 電信工程研究所
1. Introduction拆迁计划
For normal desktop computer, power management (PM) is ud to reduce power consumption and reduce cooling requirements. Lower power consumption means lower heat dissipation, which increas system stability, and less energy u, which saves money and reduces the impact on the environment. For mobile device and embedded system device, it’s much more important becau the battery power is very limited. Nowadays, android phone and iPhone are more and more pervasive. There are more and more nsors and I/O in mobile device that can be ud to improve the effectiveness of PM. The PM needs to be tuned for new mobile device’s need. In this survey, we want to not only know the power management system ud before, but also want to compare them with the design of Android PM.
男人压力大2. How does power management system work?
One power management standard for computers is ACPI, which superdes APM. All recent (consume
r) computers have ACPI support. Why ACPI has more advantage than APM? We’ll write a brief introduction both of them and compare the difference.
APM (Advanced Power Management) APM consists of one or more layers of software that support power management in computers with power manageable hardware. APM defines the hardware independent software interface between hardware-specific power management software and an operating system power management policy driver. It masks the
details of the hardware, allowing higher-level software to u APM without any knowledge of the hardware interface.
The APM software interface specification defines a layered cooperative environment in which applications, operating systems, device drivers and the APM BIOS work together to reduce power consumption. In brief, APM can extend the
用继续造句life of system batteries and thereby increas productivity and system availability.
ACPI (Advanced Configuration & Power Interface) The ACPI specification was developed to establish industry common interfaces enabling robust operating system (OS)-directed motherboard d
evice configuration and power management of both devices and entire systems. Different from APM, ACPI allows control of power management from within the operating system. The previous industry standard for power management, APM, is controlled at the BIOS level. APM is activated when the system becomes idle. The longer the system idles, the less power it consumes (e.g. screen saver vs. sleep vs. suspend). In APM, the operating system has no knowledge of when the system will change power states. There are veral software components that ACPI has: A subsystem which controls hardware states and functions that may have previously been in the BIOS configuration The states include: Thermal control Motherboard configuration Power states (sleep, suspend) a policy manager, which is software that sits on top of the operating system and allows ur input on the system policies The ACPI also has device drivers tho control/monitor devices such as a laptop battery, SMBus (communication/transmission path) and EC (embedded controller).
Figure 2.1
CPI architecture四年级手抄报
Figure 2.2墨水瓶事件
CPI power state transition diagram
Table 2.1 APM
comparison between APM and ACPI ACPI
o. Control resides in BIOS. o. Us activity timeouts to determine when to power down a device o. Bios rarely ud in embedded systems o. Makes power-management decisions management without informing OS or individual applications o. No knowledge off add-in cards or new in devices (e.g. USB, IEEEE 1394)
o. Control divided between BIOS and OS o. Decisions managed through the OS. Enables sophisticated power policy for general-purpo computers with standard purpo usage patterns and hardware o. No knowledge of device-specific specific scenarios (e.g. Need to provide predictable respon times or to respond to critical events over extended period) o. More power state means more spe specific adjustment to save power.
Figure 2.3
ACPI Monitor Usages自信的名言名句
We can either u “acpi -V” or look in each of the acpi files individually for information about our syst
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em. Check in the /proc/acpi directory for various things of importance. If you want to check your battery we can read the following file like this: cat/proc/acpi/battery/BAT1/state.
3. The Concept of Android power management
First of all, Android OS design is bad on Linux kernel. Linux has its own power management that we have described in previous ction. The following diagram (Figure 3.1) shows the main components of the Android OS.
扫黄打非宣传内容Figure 3.1
Android architecture
Android inherits many kernel components from Linux including power management component. Original power management of Linux is designed for personal computers, so there are some power saving status such as suspend and hibernation. However, the mechanisms of Linux PM do not satisfied and suitable for mobile devices or embedded systems. Mobile devices such as cell phones are not as same as PCs that have unlimited power supply. Becau mobile devices have a hard constraint of limited battery power capacity, they need a special power management mechanism. Therefore, Android has an additional methodology for power saving.
