Power Management Discussion

1
Power ManagementDiscussion

• Hiroki Kaminaga
• Sony Corporation
• kaminaga_at_sm.sony.co.jp
• translated by ikoma_at_slab.tnr.sharp.co.jp

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Goal

• Want to shorten start up time of application

HW Initialization
Mounting drivers init
Startup time of application
(Boot loader / kernel)
1 s
1 s
2 s
5 s

• Processing until the application reaches to
  main()
• Transfer of image
• Dynamic linking
• Global constructors
• IPC Processing among applications for the whole
  system running

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Conventional Approaches

• Reduce dynamic linking time
• prelink
• Reduce time for global constructors
• Put constructors in the same place(Localization
  effect)
• Execute in place (XIP)
• Demand Paging of Data Section(From Mizuyamas
  presentation in the previous Jamboree)

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Our Approaches

• Use return from hibernation
• (1) BIOS (Boot loader) level
• (2) Kernel level
• (3) BIOS kernel

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Suspend/Resume Sequence(1)
KERNEL
I/O save
Image save
I/O init
Image restore
I/O rest.
BOOT LOADER
OFF
ON
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Suspend/Resume Sequence (2)
KERNEL
I/O save
Image save
I/O init
Image restore
boot
I/O rest.
I/O s.d.
BOOT LOADER
OFF
ON
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Suspend/Resume Sequence (3)
KERNEL
I/O save
img save
I/O init
img rest
I/O rest.
I/O save
img save
I/O init
img rest
I/O rest.
BOOT LOADER
BOOT LOADER
OFF
ON
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Comparison of Three Approaches

• (1) BIOS (Boot loader) level
• Relatively faster resume from hibernation
• Complicated processing required when data
  integrity lost
• (2) Kernel level
• Can process to ensure the data integrity after
  resume from hibernation
• Slower resume from hibernation
• (3) BIOS kernel
• Fast resume from hibernation
• Can process to ensure the data integrity

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Basic ideas

• Startup
• Reduce processing until the un-hibernate on
  kernel side, using helper function of Boot loader
• DEFERRED_RESUME
• Start up the specified application with high
  priority
• Saving system image
• To start always with the same state
• Others
• Mount
• Splash window
• High speed shutdown

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Hibernation on Linux

• Swsusp
• Included in 2.6 vanilla kernel(Documentation/powe
  r/swsusp.txt)
• Author Pavel Machek
• Software suspend 2
• http//www.suspend2.net/
• Author Nigel Cunningham

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Hibernate on Linux(comparison)
swsusp
suspend2
Source http//www.suspend2.net/features
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Environment

• Target board
• OMAP Starter Kit (OSK 5912)
• OS
• Linux 2.6
• Boot loader
• U-boot

Hardware Features ARM9 core operating at 192
Mhz. DSP core operating at 192 Mhz. TLV320AIC23
Stereo Codec 32 Mbyte DDR SDRAM 32 Mbyte Flash
ROM RS-232 Serial Port 10 MBPS Ethernet port
USB Host Port Compact flash connector On board
IEEE 1149.1 JTAG
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Work Items

• Choosing hibernation on Linux
• Trying with swsusp first
• Porting to ARM
• Hibernation onto FLASH
• Saving system image
• High speed shutdown
• Hibernation on Boot loader
• DEFERED_RESUME

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Current status

• Investigating Suspend2
• Compression of system image
• Encryption of system image
• Porting Suspend2 onto ARM
• Investigating U-boot
• Hibernation on Boot loader side

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Demo
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Community

• Sent ARM port patch to Suspend2 ML Accepted
  favarably.
• ARM ML adviced me on questions/issues

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EOF
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