Android internalsEgor ElizarovSPbSU 2012

Egor Elizarov SPbSU 20122

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Egor Elizarov SPbSU 20123

Lecture 9

Power Management

Input subsystem

Sensors

Data storage

yegor.yelizarov(at)gmail.com

http://vk.com/android_internalsRev: 1.1Last update: 06/01/2012

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Previous time

Linux boot flow

Android boot flow

Android init

Main media related services

Standard media player components

Video HW acceleration

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Power Managment basics

An idle CPU should only wake up when needed

Unused hardware and devices should be disabled completely

Low activity should translate to low wattage

PM standards– ACPI (Advanced Configuration and Power Interface) -

Mostly x86 specific

– APM (Advanced Power Management) - outdated

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Linux suspend/resume flow

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Android Power Managment

Wakelocks

Early Suspend (disable some devices)

Interaction with kernel through SysFs

Android kernel PM on top of Linux PM

WakeLock Type CPU Screen Keyboard

PARTIAL_WAKE_LOCK On* Off Off

SCREEN_DIM_WAKE_LOCK On Dim Off

SCREEN_BRIGHT_WAKE_LOCK On Bright Off

FULL_WAKE_LOCK On Bright Bright

*If you hold a partial wakelock, the CPU will continue to run, irrespective of any timers and even after the user presses the power button. In all other wakelocks, the CPU will run, but the user can still put the device to sleep using the power button.

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Power Managment subsystem

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HID Input device classes

Keyboards (qwerty, hard keys)

Cursor (Mouse, trackball)

Multitouch (Touchscreen)

External (IR/Bluetooth remote control)

etc. (frameworks/base/services/input/EventHub.h)

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Input subsystem

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Control points

Driver and Firmware Configuration

Board Configuration Properties

Resource Overlays (frameworks/base/core/res/res/values/config.xml)

Key Maps (Ex: device/samsung/tuna/tuna-gpio-keypad.kl)

Input Device Configuration Files (Ex: device/samsung/tuna/Melfas_MMSxxx_Touchscreen.idc)

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Event codes

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System files

● Key layout files (device/samsung/tuna/tuna-gpio-keypad.kl)

● Key character map files (device/samsung/tuna/tuna-gpio-keypad.kl)

● Input device configuration files (device/samsung/tuna/Melfas_MMSxxx_Touchscreen.idc)

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Sensor types

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Sensor subsystem

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HAL/Kernel interaction

No unified interface

SysFs

DevFs

Industrial input output system (kernel/drivers/staging/iio)

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Sensor settings

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Input noise reduction

Needed for both sensors and input devices

Usually implemented in HW or FW

Precision vs jittering

Using of previous/next values

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Raw data example

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Noise reduction approaches

Polynomial approximation

Evaluation of derivatives

Integrators

Kalman filters

etc

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Data storage

Shared preferencies

Internal storage

External storage

SQLite DB

Network connection

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FS types

RootFs (linux permission support) Ext* yaffs ubifs

● External storage (same uid/gid for all files) Fat Ntfs / ntfs-3g

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External storage

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SQLite DB

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Next Time

Profiling / Debugging

WiFi / BT / RIL

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Useful links

http://vk.com/android_internals

http://docs.fedoraproject.org/en-US/Fedora/15/html/Power_Management_Guide/index.html

http://kzjblog.appspot.com/2010/11/20/suspend-en.html

http://developer.android.com/reference/android/os/PowerManager.html

http://source.android.com/tech/input/overview.html

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Useful links (2)

http://developer.android.com/guide/topics/sensors/index.html

Savitzky, A.; Golay, M.J.E. (1964). "Smoothing and Differentiation of Data by Simplified Least Squares Procedures". Analytical Chemistry 36 (8): 1627–1639. doi:10.1021/ac60214a047

http://developer.android.com/guide/topics/data/data-storage.html

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Thanks to

Sergey Matyukevich for review and advices (www.linkedin.com/pub/sergey-matyukevich/31/889/769)

Nikolay F. Fominykh for review and advices

Vladimir Barinov for review and advices (http://www.linkedin.com/pub/vladimir-barinov/2a/18a/bab)