The document discusses various topics related to Android internals including power management, input subsystems, sensors, and data storage. It describes the Linux and Android approaches to power management including wakelocks and suspend/resume. It also outlines the different types of input devices, sensor types, and approaches to handling sensor data and reducing noise. Finally, it briefly discusses the various options for data storage in Android.

1. Android internals
Egor Elizarov
SPbSU 2012

2. Legal info
 Android internals by Egor Elizarov is licensed under a
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 Corrections, suggestions, contributions and translations are welcome!
2 Egor Elizarov SPbSU 2012

3. Lecture 9
Power Management
Input subsystem
Sensors
Data storage
yegor.yelizarov(at)gmail.com
Rev: 1.1 http://vk.com/android_internals
Last update: 06/01/2012
3 Egor Elizarov SPbSU 2012

4. 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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5. 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– APM (Advanced Power Management) - outdated
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6. Linux suspend/resume flow
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7. Android Power Managment

Wakelocks
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.

Early Suspend (disable some devices)

Interaction with kernel through SysFs

Android kernel PM on top of Linux PM
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8. Power Managment subsystem
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9. 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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10. Input subsystem
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11. 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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12. Event codes
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13. 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_T
ouchscreen.idc)
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14. Sensor types
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15. Sensor subsystem
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16. HAL/Kernel interaction

No unified interface

SysFs

DevFs

Industrial input output system
(kernel/drivers/staging/iio)
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17. Sensor settings
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18. 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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19. Raw data example
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20. Noise reduction approaches

Polynomial approximation

Evaluation of derivatives

Integrators

Kalman filters

etc
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21. Data storage

Shared preferencies

Internal storage

External storage

SQLite DB

Network connection
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22. 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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23. External storage
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24. SQLite DB
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25. Next Time

Profiling /
Debugging

WiFi / BT / RIL
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26. 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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27. 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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28. 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)
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