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Linux Bootup Time Reduction for Digital Still Camera. Chan Ju, Park SW Laboratories Samsung Electronics. Agenda. Introduction DSC Bootup Procedure Bootup time reduction methods Boot loader Kernel Root File system Application Optimization Suspend/resume Results Further works

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linux bootup time reduction for digital still camera

Linux Bootup Time Reduction for Digital Still Camera

Chan Ju, Park

SW Laboratories

Samsung Electronics

  • Introduction
  • DSC Bootup Procedure
  • Bootup time reduction methods
    • Boot loader
    • Kernel
    • Root File system
    • Application Optimization
    • Suspend/resume
  • Results
  • Further works
  • Conclusion
  • DSC
    • Digital still camera
  • Bootup time
    • The time from platform power on to preview state
  • Preview state
    • The DSC state for ready-to-shot
  • 3A
    • Auto focus, auto white balance, auto expose
  • Suspend/resume
    • Suspend to dram
  • RFS
    • Root file system for Linux Kernel
  • Robust FS
    • Linux file system for OneNAND flash
  • Normal boot, suspend/resume boot
  • About this project
    • In samsung, Embedded Linux ported for many CE devices
      • DTV, DMB, Mobile phone, DVR, other set top boxes, etc
    • But not DSC area
    • DSC use many RTOSes ( vxworks, pSos, uITRON, Nucleus, etc)
    • Project stated for evaluation of embedded linux
  • Why Linux in DSC
    • Technical Convergence in CE Devices
    • Plentiful of Application
    • Open S/W Platform
    • Cost?
Embedded Linux on DSC
    • There exist only few cases which was published
    • E.g. Ricoh Company made prototype Linux DSC
  • DSC & bootup time
    • Long bootup time diminish customer satisfaction
    • Bootup Time is more important in DSC
Linux Bootup Time
    • PC : 1 min or more
    • Embedded System : 2~10 sec
    • Depends on system, Applications, Policy
      • Image loading, H/W peripherals, application init
  • applied Bootup methods for DSC
    • Normal Boot
      • bootloader ~ preview application running
    • Suspend/Resume
      • using suspend-to-ram
  • Goals
    • Normal boot : 2 sec
    • Suspend/resume : 1 sec
test environments
Test Environments
  • Target Platform
    • Core
      • ARM926EJS
    • Image processor
      • Samsung S5C7380x
    • System clock
      • 216Mhz Fclock,108Mhz Hclock
    • Memory
      • 64MB DDR,
      • 64MB One-NAND flash ( async mode )
    • DSC Module & etc
      • 6M CCD(CMOS) censor, AF/Zoom/Shutter/Iris motor, Digital LCD, JPEG/MPEG codec, etc.
      • USB, ADC, SD/MMC Card, etc
  • Kernel
    • 2.4.20
    • Non-compressed Image
    • Size : about 1MB
  • File System
    • Root fs : Cramfs
    • Robust FS for Flash filesystem in OneNAND
bootup time reduction is
Bootup time reduction is
  • Every little makes a mickle
  • All kinds of techniques are needed
    • Firmware (boot loader)
      • Minimal system init
      • shortening image copy time
      • Boot devices
    • Hardware initialization
      • One time System initialization
      • Remove H/W probing time
      • Only initialize the device which was used when bootup
      • E.g. Dsc motors, storage (HDD, Card, Flash), DSP, etc
Image small sizing
    • kernel, root fs (libraries), D/D Modules, etc
    • Depends on the kernel configuration
  • Device driver initialization
    • Remove H/W probing & Initialization
    • Using hard coding
    • Module loading policy
      • Using static module if needed
      • Other modules can load when needed
  • application optimization
    • Resource loading
    • Memory allocation
    • App setup procedure
  • Suspend/resume
    • reset ~ OneNAND boot loader(xloader) execute
    • xloader copied to SDRAM & execute at SDRAM
    • xloader copy u-boot to RAM
    • DSC motor init
    • u-boot execute & copy kernel Image to SDRAM
  • kernel init
    • Kernel Init code execute
    • init kernel subsystem
    • init static module
    • mount cramfs
    • execute init script
  • application init
    • execute basic DSC application module
    • setup preview mode sequence
    • display preview & OSD Image
boot time measurements
Boot time measurements
  • Using H/W devices
    • Expensive
    • Target code modification is needed
    • Exact
  • Using serial outputs
    • ARM or MIPS has no counter register (x86:TSC reg.)
    • Using host serial in cross development environments
    • features
      • Cheap
      • No or few modification for the target code
      • Can collect much data
      • Comparatively small differences
initial bootup time before optimization
Initial bootup time (before optimization)
  • Just after kernel and D/D porting
  • Using NAND flash, zImage
applied methods
Applied methods
  • Normal bootup
    • bootloader
      • OneNAND booting (more faster than Nand flash, 2 times)
    • Kernel / device driver
      • use Preset LJP (Loop Per Jiffies)
      • module init optimization
      • use non-compressed kernel image
      • size optimization ( kernel, library )
      • remove kernel message
    • File system
    • application optimization
  • Suspend/resume
Boot loader
  • Not using u-boot except development period
  • Boot loader
    • initializes a system
    • loads the Kernel image into RAM
  • Minimal initialization
    • Memory, clock
  • Boot device
    • NAND Flash
    • OneNAND Flash
      • When power on, xloader (1KB bootloader of OneNAND flash) is executed automatically
      • hardly influence to bootup time
      • More fast than nand flash (2 times)
flash partition usage onenand flash
Flash Partition Usage (OneNAND flash)



‘boot’ partition


bootloader paramters

‘param’ partition


Linux Kernel Image

‘kernel’ partition



(Code & Library files)

‘root’ partition


Robust FS

(System Config Files &

User Data Files)

‘Robust FS’ partition

Reserved Area


kernel d d
Kernel & D/D
  • Using uncompressed Image
    • Save decompressing time
  • Preset loops_per_jiffy
    • Find out loops_per_jiffy values, and hard coding
  • Disable Console Output
    • Just add ‘quiet’ option to command line when compile
  • Remove root file system check routine
  • Concurrent driver init
    • DSC Motor has long initialization time
    • Modification zoom motor init code
      • More than 1sec
      • Motor init can be parallelized
    • Initialize at start of the bootloader
  • Remove the static device driver
    • It makes smaller kernel
    • Save the module init time at bootup
    • The modules which is not need at bootup time can be loaded after bootup.
Saving memory allocation time for Image processing
    • Using boot-time allocation methods
    • Kernel doesn’t know about area
    • Can save mem alloc time
    • Can using the big area DMA memory
      • Max : 12MB contiguous memory required (capture mode)
Root File system
  • Issues of Root File System
    • Save copy time at bootloader
    • Save decompressing time when kernel initialized
    • small size image
      • Using busy box
    • Read only nand file system
    • Modifiable directory has to mount another R/W file system
      • We use robust file system for OneNAND
      • It include bad block management algorithms
    • Partial uncompressed cramfs
      • Save decompressing time
      • Not tested at this time
application init loading
Application init & loading
  • Loading OSD data
    • When system bootup, load only need data
  • DSC application
    • If preview mode, other process creation init & loading can delay
  • Memory allocation, copy
    • Time spending
    • DSC processing much Image data
  • Storage device Init & mount time
    • Sd/mmc card initialization
    • Initialization can be delayed
  • Background processing
    • Card Device Init (device init, mount, etc)
    • storage information reading
    • Init DCF/Exif S/W module
suspend resume
Suspend / Resume
  • suspend-to-ram
  • During system suspend, the ram change to self-refresh mode
  • issues
    • The cost of suspend/resume to Ram
      • Power consumption
    • Self refresh mode of DRAM
    • power off all devices except but RAM
    • Boot flags registers
      • If it locates at DSP, consume more power
      • Using power management unit (PMU)
    • Other information will be stored at global variables in DRAM
      • CPU register, stack, I/O register values
system suspend procedure
System suspend procedure

Power off Button Push

CPU Register Save to RAM

IO Register Contents save to RAM

Set to self refresh mode of RAM

Save flag of fast boot to PMU Register

Power off CPU &

all devices except PMU & RAM

system resume procedure
System resume procedure

Normal boot process

Resume boot process

Power on

PMU power on

Reset vector

Boot loader

Restore HW register values

DSC H/W init

Set interrupt for resume

Disable Interrupt

Restore variables &

CPU register values

Check if suspended


DSC HW / App init &

Check DSC Mode


Clock, Memory Init

Execute DSC app

Kernel loading & jump

* PMU: Power Management Unit

results of suspend resume
Results of suspend/resume
  • from reset to preview state
    • About 800 ms
  • For power saving
    • It is possible to full shutdown when user does not operate during settled time
excepted methods
Excepted methods
  • Kernel XIP
    • Executing code directly from flash
    • Reduce boot time and save cost, etc
    • Current platform has no proper devices (e.g Nor Flash)
  • Parallelizing of services execution
    • applying techniques of parallelizing RC-scripts at system / user space start up
    • Effectiveness depends on the number of services
    • Embedded system such as DSC has not many services
further works
Further works
  • prelink (library execution optimization)
  • Bootcache
  • Suspend-to-disk
  • Boot process analyzing with tools
    • Ex) Bootchart
  • optimized block copy in OneNAND
    • OneNAND cached copy
    • synchronous mode
  • There exist many methods for reducing the Linux Bootup time
  • The Reduction methods are variant

from the DSC H/W or scenario,

So we have to choice the proper policy.

  • Linux Bootup methods for DSC
    • normal boot
    • Suspend/resume
  • Many reduction methods can be adopted but,
    • choice & evaluation is needed
  • Embedded Linux can satisfy the requirements of DSC Bootup time
  • Linux on a Digital Camera, Porting 2.4 Linux kernel to an existing digital camera,Alain Volmat, Ricoh Company Ltd.
  • Methods to Improve Bootup Time in LinuxTim R. Bird, Sony Electronics
  • IBM developer white paper, “Boot linux faster, parallelize Linux system services to improve boot speed”|