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分类: LINUX

2009-08-31 22:41:12

The default Blackfin development board Linux and User-Space configuration examples, are optimized for ease of use and flexibility, and not for size and startup time.There are hundreds of options enabled by default, allowing you to test drive various Linux drivers and application examples. Or there are options only useful during development and debugging. Having these options in an embedded production system is pointless.

Small memory footprint, low and a time are typically in the interest of the embedded system designer.

This capture illustrates a 1 Second boot. For instrumentation I used GPIOs.

Configuration:

  • Linux-2.6.24
  • Standard kernel features including MTD/Block Layer support, but without TCP/IP Networking and kernel debug facilities.
  • Rootfs in Initial RAM filesystem and RAM disk (initramfs/initrd).
Section Time Spend Comments
Boot Bootloader 20ms Time between RESET High and u-boot invoking bootcmd=bootm 0x20040000
Bootloader loading u(vm)Image 381ms Time between bootm command and executing the first kernel instruction in head.S
Linux kernel Startup 302ms Time between executing the first kernel instruction and kernel invoking /bin/init
User Space Setup 271ms Time between kernel invoking /bin/init and end of /etc/rc scrip
Total Boot Time 973ms

Config files used during this benchmark are available here:

Configuration:

  • Linux-2.6.24
  • Standard kernel features including MTD/Block Layer support, TCP/IP Networking but without kernel debug facilities.
  • Rootfs in Initial RAM filesystem and RAM disk (initramfs/initrd).
Section Time Spend Comments
Boot Bootloader 20ms Time between RESET High and u-boot invoking bootcmd=bootm 0x20040000
Bootloader loading u(vm)Image 427ms Time between bootm command and executing the first kernel instruction in head.S
Linux kernel Startup 366ms Time between executing the first kernel instruction and kernel invoking /bin/init
User Space Setup 244ms Time between kernel invoking /bin/init and end of /etc/rc scrip
Total Boot Time 1057ms

Config files used during this benchmark are available here:

  • Increase timing parameters). Typical values for BF537/527 set CCLK to 525MHz while SCLK is 131.5MHz.
  • When boot speed is a major concern, and you are trying to save a few milliseconds- avoid using SPI Flash (BFIN_BOOT_SPI_MASTER) preferably use NOR Flash, there are now generic drivers for GPIO assisted maps in u-boot and the Linux kernel allowing you to utilize more memory than actually mapped by physical address lines. With latest u-boot (starting SVN revision 1326) there is DMA SPI Flash Read support – this boosts the sequential read speed up to 3.2MByte/s.

See SPI flash boot example below: spi_boot_linux_form_processor_reset_into_user_space_in_less_than_1.4_second

  • When booting from

    See also here:

    u-boot env:
    #set bootdelay 0
    

    Once you set bootdelay 0 in u-boot and the environment I saved. The only way to revert this without reflashing u-boot is to do it from the Linux that is going to be booted, and does include the uboot-utils.

    root:/> fw_setenv bootdelay 1

    Compile u-boot with #define CONFIG_SILENT_CONSOLE

    u-boot env:
    #set silent 1
    

    u-boot env:
    #set baudrate 115200
    

    The time spend here scales linearly with the size of your image your loading into memory.

    Image sizes in the example discussed here:

    michael@mhenneri-D02:~/devel/svn/uclinux-dist-trunk_3/images> ll
    total 9600
    lrwxrwxrwx 1 michael users      18 2008-08-05 13:12 linux -> linux.initramfs.gz
    -rwxr-xr-x 1 michael users 2185567 2008-08-05 13:12 linux.initramfs
    -rwxr-xr-x 1 michael users 1816927 2008-08-05 13:12 linux.initramfs.gz
    -rw-r--r-- 1 michael users  773120 2008-08-05 13:12 rootfs.initramfs
    -rw-r--r-- 1 michael users    8236 2008-08-05 13:12 rootfs.initramfs.contents
    -rw-r--r-- 1 michael users  406936 2008-08-05 13:12 rootfs.initramfs.gz
    -rw-r--r-- 1 michael users  359142 2008-08-05 13:12 System.map.initramfs
    -rw-r--r-- 1 michael users  359142 2008-08-05 13:12 System.map.initramfs.gz
    lrwxrwxrwx 1 michael users      16 2008-08-05 13:12 uImage -> uImage.initramfs
    -rw-r--r-- 1 michael users  940474 2008-08-05 13:12 uImage.initramfs
    -rw-r--r-- 1 michael users  941208 2008-08-05 13:12 uImage.initramfs.gz
    -rw-r--r-- 1 michael users  533519 2008-08-05 13:12 vmImage
    -rwxr-xr-x 1 michael users 1398334 2008-08-05 13:12 vmlinux
    

    • Preferably use compressed images (uImage, vmImage), especially when loading from slow Flash memory.
    • Disable the checksum calculation over the complete image in the bootm command to trade speed for safety in the boot process. Note that the header checksum is still verified.

    u-boot env:
    #set verify n
    

    • Remove unused kernel features and functionality. Kernel debugging is to late in production systems, therefore remove all debug functionality.

    See this configuration can be booted in exactly 1 Second.

    • Pass loops_per_jiffy on the kernel command line lpj=xxxxxxx to the kernel. (get the value once from your kernel startup messages)

    Example:
    Calibrating delay loop... 1046.52 BogoMIPS (lpj=2093056)
    

    • Disable earlyprintk and suppress kernel messages on startup see:

    Example Kernel command line:

          root=/dev/mtdblock0 rw console=ttyBF0,115200 quiet lpj=2093056
    

    Further speedups are easily possible:

    • If your application doesn’t need to access mtd/storage other then your initial ram filesystem (initramfs/initrd), remove the block and mtd layer (approx -100ms)

    By removing more options, such as support for printk, System V IPC, etc. the overall bootime can be less than 0.7 Seconds.

    • Slim down your user space configuration by removing unused commands in busybox and by disabling other applications in the uClinux-dist.
    • Try to find the executable file format that fits best your application needs: FLAT, Shared-FLAT or FDPIC. Uncheck installation of shared libraries if you are not going to use them. Typically Shared-FLAT performs best.
    • Don’t build debugable libraries and applications: remove the –g flag form your user/lib CFLAGS.
    • Remove unused functionality from your /etc/rc script. For example don’t try to mount usbfs if you are not planning to use USB, etc.
    • Use static device nodes (/dev/) versus dynamic. Static device nodes don’t have any runtime overhead.
    • Remove options form your C-library you are not going to use such as wchar support, etc.

    In case you use static device nodes and don't mount proc and sysfs the time spend here can be as low as 20ms

    Disabling sysfs and procfs does have some negative side effects:
    sysfs
    No firmware loading (which affects most wireless cards). No power control/events. No tweaking of devices which export attributes only in sysfs (which is more and more each day but largely device-specific). No bus discovery (any bus, but for us usb is what really matters). Some more …

    procfs
    No information about running processes, filesystems, memory, network. No access to sysctl tunables (/proc/sys/)

    Boot Linux from Processor Reset into user space in 0.4 Seconds

    This capture illustrates a 0.4 Seconds boot, of minimalistic system.

    Almost all device drivers are removed except for Serial and GPIO. Kernel features such as loadable module support and many others are removed. User space only includes init, shell, ls and echo.

    This setup may fit together with the bootloader into 0.5 Mega Byte of flash memory.

    Section Time Spend Comments
    Boot Bootloader 20ms Time between RESET High and u-boot invoking bootcmd=bootm 0x20040000
    Bootloader loading u(vm)Image 168ms Time between bootm command and executing the first kernel instruction in head.S
    Linux kernel Startup 224ms Time between executing the first kernel instruction and kernel invoking /bin/init
    User Space Setup 9ms Time between kernel invoking /bin/init and end of /etc/rc scrip
    Total Boot Time 421ms

    The config files used can be downloaded here:

    Config Files

    michael@mhenneri-D02:~/devel/svn/uclinux-dist-trunk_3/linux-2.6.x> bfin-uclinux-size vmlinux */built-in.o
       text    data     bss     dec     hex filename
     713068   54280   17604  784952   bfa38 vmlinux
      69558    3692    3428   76678   12b86 drivers/built-in.o
     116032    1224    1748  119004   1d0dc fs/built-in.o
      13820    2509    1128   17457    4431 init/built-in.o
      95120    7176    5488  107784   1a508 kernel/built-in.o
      19028      12      16   19056    4a70 lib/built-in.o
      44700    2852     508   48060    bbbc mm/built-in.o
        120       0       0     120      78 net/built-in.o
       1352       4       4    1360     550 security/built-in.o
     305664       0       0  305664   4aa00 usr/built-in.o
    

    michael@mhenneri-D02:~/devel/svn/uclinux-dist-trunk_3/images> ll
    total 4180
    lrwxrwxrwx 1 michael users     18 2008-08-05 15:16 linux -> linux.initramfs.gz
    -rwxr-xr-x 1 michael users 939908 2008-08-05 15:16 linux.initramfs
    -rwxr-xr-x 1 michael users 796548 2008-08-05 15:16 linux.initramfs.gz
    -rw-r--r-- 1 michael users 305664 2008-08-05 15:16 rootfs.initramfs
    -rw-r--r-- 1 michael users   6895 2008-08-05 15:16 rootfs.initramfs.contents
    -rw-r--r-- 1 michael users 164813 2008-08-05 15:16 rootfs.initramfs.gz
    -rw-r--r-- 1 michael users 125155 2008-08-05 15:16 System.map.initramfs
    -rw-r--r-- 1 michael users 125155 2008-08-05 15:16 System.map.initramfs.gz
    lrwxrwxrwx 1 michael users     16 2008-08-05 15:16 uImage -> uImage.initramfs
    -rw-r--r-- 1 michael users 415208 2008-08-05 15:16 uImage.initramfs
    -rw-r--r-- 1 michael users 416145 2008-08-05 15:16 uImage.initramfs.gz
    -rw-r--r-- 1 michael users 250272 2008-08-05 15:16 vmImage
    -rwxr-xr-x 1 michael users 623513 2008-08-05 15:16 vmlinux
    

    This example uses a similar configuration than the first 1 Sec. boot from to read more.

    Test Setup
    u-boot-1.1.6

     SPI Fast Boot Example

    Configuration:

    • Standard kernel features including MTD/Block Layer support, but without TCP/IP Networking and kernel debug facilities.
    • JFFS2 Rootfs in

      Section Time Spend Comments
      Boot Bootloader 35ms Time between RESET High and u-boot invoking bootcmd=eeprom read 0x1000000 0x40000 8b7ff;bootm
      Bootloader loading vmImage 364ms Time between eeprom read command and executing the first kernel instruction in head.S
      Linux kernel Startup 539ms Time between executing the first kernel instruction and kernel invoking /bin/init
      User Space Setup 423ms Time between kernel invoking /bin/init and end of /etc/rc scrip
      Total Boot Time 1.36s

      michael@mhenneri-D02:~/devel/svn/uclinux-dist-trunk_3/linux-2.6.x> bfin-uclinux-size vmlinux */built-in.o
         text    data     bss     dec     hex filename
       949649   64356   49016 1063021  10386d vmlinux
        32606     962    1080   34648    8758 block/built-in.o
       121916    4794    3828  130538   1fdea drivers/built-in.o
       302511    2560    2132  307203   4b003 fs/built-in.o
        16807    2509    1128   20444    4fdc init/built-in.o
        14176     684       0   14860    3a0c ipc/built-in.o
       155093   12968   30476  198537   30789 kernel/built-in.o
        35164      72    2296   37532    929c lib/built-in.o
        71212    3740     576   75528   12708 mm/built-in.o
       119772    3972    1796  125540   1ea64 net/built-in.o
         2522       0       0    2522     9da security/built-in.o
          133       0       0     133      85 usr/built-in.o
      

      lrwxrwxrwx 1 michael users      18 2008-08-21 17:26 linux -> linux.initramfs.gz
      -rwxr-xr-x 1 michael users 2130338 2008-08-21 17:26 linux.initramfs
      -rwxr-xr-x 1 michael users 1827234 2008-08-21 17:26 linux.initramfs.gz
      -rw-r--r-- 1 michael users  643072 2008-08-21 17:25 rootfs.initramfs
      -rw-r--r-- 1 michael users   12071 2008-08-21 17:25 rootfs.initramfs.contents
      -rw-r--r-- 1 michael users  343870 2008-08-21 17:25 rootfs.initramfs.gz
      -rw-r--r-- 1 michael users  430228 2008-08-21 17:25 rootfs.jffs2
      -rw-r--r-- 1 michael users  377012 2008-08-21 17:26 System.map.initramfs
      -rw-r--r-- 1 michael users  377012 2008-08-21 17:26 System.map.initramfs.gz
      lrwxrwxrwx 1 michael users      16 2008-08-21 17:26 uImage -> uImage.initramfs
      -rw-r--r-- 1 michael users  915303 2008-08-21 17:26 uImage.initramfs
      -rw-r--r-- 1 michael users  916128 2008-08-21 17:26 uImage.initramfs.gz
      -rw-r--r-- 1 michael users  571390 2008-08-21 17:25 vmImage
      -rwxr-xr-x 1 michael users 1473255 2008-08-21 17:25 vmlinux
      

      Configuration:

      • Standard kernel features including MTD/Block Layer support, with TCP/IP Networking but without kernel debug facilities.
      • JFFS2 Rootfs in

        Section Time Spend Comments
        Boot Bootloader 35ms Time between RESET High and u-boot invoking bootcmd=eeprom read 0x1000000 0x40000 8b7ff;bootm
        Bootloader loading vmImage 436ms Time between eeprom read command and executing the first kernel instruction in head.S
        Linux kernel Startup 521ms Time between executing the first kernel instruction and kernel invoking /bin/init
        User Space Setup 451ms Time between kernel invoking /bin/init and end of /etc/rc scrip
        Total Boot Time 1.44s

        michael@mhenneri-D02:~/devel/svn/uclinux-dist-trunk_3/linux-2.6.x> bfin-uclinux-size vmlinux */built-in.o
           text    data     bss     dec     hex filename
        1982319   74400   55416 2112135  203a87 vmlinux
          32606     962    1080   34648    8758 block/built-in.o
           3299      36       8    3343     d0f crypto/built-in.o
         136690    5270    3860  145820   2399c drivers/built-in.o
         302511    2560    2132  307203   4b003 fs/built-in.o
          16807    2509    1128   20444    4fdc init/built-in.o
          14176     684       0   14860    3a0c ipc/built-in.o
         155093   12968   30476  198537   30789 kernel/built-in.o
          35164      72    2296   37532    929c lib/built-in.o
          71212    3740     576   75528   12708 mm/built-in.o
         332314   13772    8164  354250   567ca net/built-in.o
           2522       0       0    2522     9da security/built-in.o
         803840       0       0  803840   c4400 usr/built-in.o
        

        lrwxrwxrwx 1 michael users      18 2008-08-21 16:24 linux -> linux.initramfs.gz
        -rwxr-xr-x 1 michael users 2597785 2008-08-21 16:25 linux.initramfs
        -rwxr-xr-x 1 michael users 2220953 2008-08-21 16:24 linux.initramfs.gz
        -rw-r--r-- 1 michael users  803840 2008-08-21 16:24 rootfs.initramfs
        -rw-r--r-- 1 michael users   12783 2008-08-21 16:24 rootfs.initramfs.contents
        -rw-r--r-- 1 michael users  429021 2008-08-21 16:24 rootfs.initramfs.gz
        -rw-r--r-- 1 michael users  529440 2008-08-21 16:24 rootfs.jffs2
        -rw-r--r-- 1 michael users  432847 2008-08-21 16:25 System.map.initramfs
        -rw-r--r-- 1 michael users  432847 2008-08-21 16:24 System.map.initramfs.gz
        lrwxrwxrwx 1 michael users      16 2008-08-21 16:25 uImage -> uImage.initramfs
        -rw-r--r-- 1 michael users 1142481 2008-08-21 16:25 uImage.initramfs
        -rw-r--r-- 1 michael users 1141928 2008-08-21 16:24 uImage.initramfs.gz
        -rw-r--r-- 1 michael users  713205 2008-08-21 16:24 vmImage
        -rwxr-xr-x 1 michael users 1775055 2008-08-21 16:24 vmlinux
        

        For more information see here:

        • Set

          Index: include/configs/bf537-stamp.h
          ===================================================================
          #define CONFIG_BFIN_BOOT_MODE			BFIN_BOOT_SPI_MASTER
          #define CONFIG_VCO_MULT				21
          #define CONFIG_SCLK_DIV				4
          
          #define CONFIG_EBIU_SDRRC_VAL  			0x3F8
          #define CONFIG_EBIU_SDGCTL_VAL 			0x009111CD
          
          #define CONFIG_SPI
          #define CONFIG_SPI_BAUD				2
          #define CONFIG_SPI_BAUD_INITBLOCK		2
          
          #undef CONFIG_RTC_BFIN
          #define CONFIG_SILENT_CONSOLE
          

          baudrate=57600
          loads_echo=1
          ipaddr=192.168.0.15
          serverip=192.168.0.2
          autoload=no
          rootpath=/romfs
          gatewayip=192.168.0.1
          netmask=255.255.255.0
          hostname=bf537-stamp
          loadaddr=0x1000000
          ubootfile=u-boot.ldr
          update=tftp $(loadaddr) $(ubootfile);eeprom write $(loadaddr) 0x0 $(filesize)
          addip=set bootargs $(bootargs) ip=$(ipaddr):$(serverip):$(gatewayip):$(netmask):$(hostname):eth0:off
          ramargs=set bootargs root=/dev/mtdblock0 rw earlyprintk=serial,uart0,57600 console=ttyBF0,57600
          ramboot=tftp $(loadaddr) uImage;run ramargs;run addip;bootm
          nfsargs=set bootargs root=/dev/nfs rw nfsroot=$(serverip):$(rootpath),tcp,nfsvers=3
          nfsboot=tftp $(loadaddr) vmImage;run nfsargs;run addip;bootm
          flashboot=bootm 0x20100000
          ethaddr=00:E0:22:FE:52:3A
          ethact=Blackfin EMAC
          verify=n
          bootcmd=eeprom read 0x1000000 0x40000 8b7ff;bootm
          silent=y
          stdin=serial
          stdout=nc
          stderr=nc
          bootargs=root=/dev/mtdblock2 rw rootfstype=jffs2 console=ttyBF0,57600 quiet lpj=2093056
          bootdelay=0
          

          Some Flash Memory Technologies require a specially structured JFFS2 filesystem image. Therefore additional flags for mkfs.jffs2 must be given during the uClinux-dist build process.

          For ATMEL Binary Page Size DataFlash use these options:

          make MKFS_JFFS2_FLAGS='-e 0x2000 -n'

          Typically it's more convenient updating flash partitions in Linux.

          root:/> modprobe mtdchar
          root:/> flash_eraseall -j /dev/mtd2
          Erasing 0 Kibyte @ 2dfe00 -- 99 % complete.
          root:/> cp /var/rootfs.jffs2 /dev/mtd2
          root:/> cp /var/vmImage /dev/mtd1   
          

          root:/> cat /etc/rc
          # This file targets a *development* system.  Many things are not
          # needed for *production* systems.  Comment out what you do not need.
          
          #hostname blackfin
          
          mount -t proc proc /proc -o noexec,nosuid,nodev
          mount -t sysfs sysfs /sys -o noexec,nosuid,nodev
          
          #
          # Setup dynamic /dev and let mdev manage it for us
          #
          #if [ -e /bin/mdev ] ; then
          #       mount -t tmpfs mdev /dev -o exec,nosuid,mode=0755,size=10M
          #       [ -e /proc/sys/kernel/hotplug ] && echo /bin/mdev > /proc/sys/kernel/hotplug
          #       /bin/mdev -s
          #fi
          
          #
          # Setup dynamic pseudo-terminal file system ... needed by any system that
          # uses telnet or ssh (like dropbear) rather than the old static pty system.
          # You should give this a dedicated gid and set the mode to 0650.
          #
          mkdir -p /dev/pts
          mount -t devpts devpts /dev/pts -o noexec,nosuid
          
          #
          # Give the log/state/runtime files in /var temporary storage that'll be
          # lost when we reboot.
          #
          mount -t ramfs var /var
          mkdir /var/tmp /var/log /var/run /var/lock
          
          #
          # Give temp files a read/write location not in flash/etc...
          #
          mount -t tmpfs tmp /tmp -o nosuid,nodev
          
          #
          # Needed if you plan on doing anything USB related
          #
          #[ -d /proc/bus/usb ] && mount -t usbfs usbfs /proc/bus/usb
          
          #
          # Needed if you run an NFS server on the board
          #
          #grep -qs nfsd /proc/filesystems && mount -t nfsd nfsd /proc/fs/nfsd
          
          #
          # Useful for debugging only
          #
          #[ -d /sys/kernel/debug ] && mount -t debugfs debugfs /sys/kernel/debug
          
          #
          # Create your own interpreters for random file formats
          #
          #[ -d /proc/sys/fs/binfmt_misc ] && mount -t binfmt_misc binfmt_misc /proc/sys/fs/binfmt_misc
          
          #
          # User interface to security modules (selinux, etc...)
          #
          #[ -d /sys/kernel/security ] && mount -t securityfs securityfs /sys/kernel/security
          
          #
          # Do random network setup
          #
          #dhcpcd &
          #ifconfig eth0 10.100.4.251 up
          #ifconfig lo 127.0.0.1
          #inetd &
          
          #cat /etc/issue
          #cat /etc/motd
          

          Linux version 2.6.26.2-ADI-2009R1-pre-svn5184-dirty8 (michael@mhenneri-D02) (gcc version 4.1.2 (ADI svn)) #5648 Thu Aug 21 16:19:22 CEST 2008
          Board Memory: 64MB
          Kernel Managed Memory: 64MB
          Memory map:
            fixedcode = 0x00000400-0x00000490
            text      = 0x00001000-0x000e6dd0
            rodata    = 0x000e6de0-0x00111da8
            bss       = 0x00111dc0-0x0011f638
            data      = 0x0011f638-0x0012e000
              stack   = 0x0012c000-0x0012e000
            init      = 0x0012e000-0x00141000
            available = 0x00141000-0x03eff000
            DMA Zone  = 0x03f00000-0x04000000
          Hardware Trace Active and Enabled
          Blackfin support (C) 2004-2008 Analog Devices, Inc.
          Compiled for ADSP-BF537 Rev 0.3
          Blackfin Linux support by 
          Processor Speed: 525 MHz core clock and 131 MHz System Clock
           boot memmap: 0000000000141000 - 0000000003eff000 (usable)
          On node 0 totalpages: 16127
            DMA zone: 126 pages used for memmap
            DMA zone: 0 pages reserved
            DMA zone: 16001 pages, LIFO batch:3
            Normal zone: 0 pages used for memmap
            Movable zone: 0 pages used for memmap
          NOMPU: setting up cplb tables for global access
          Instruction Cache Enabled
          Data Cache Enabled (write-back)
          Built 1 zonelists in Zone order, mobility grouping off.  Total pages: 16001
          Kernel command line: root=/dev/mtdblock2 rw rootfstype=jffs2 console=ttyBF0,57600 quiet lpj=2093056
          Configuring Blackfin Priority Driven Interrupts
          PID hash table entries: 256 (order: 8, 1024 bytes)
          console [ttyBF0] enabled
          Dentry cache hash table entries: 8192 (order: 3, 32768 bytes)
          Inode-cache hash table entries: 4096 (order: 2, 16384 bytes)
          Kernel managed physical pages: 16127
          Memory available: 62644k/65536k RAM, (76k init code, 919k kernel code, 285k data, 1024k dma, 584k reserved)
          Calibrating delay loop (skipped)… 1046.52 BogoMIPS preset
          Mount-cache hash table entries: 512
          Blackfin Scratchpad data SRAM: 4 KB
          Blackfin L1 Data A SRAM: 16 KB (15 KB free)
          Blackfin L1 Data B SRAM: 16 KB (16 KB free)
          Blackfin L1 Instruction SRAM: 48 KB (42 KB free)
          net_namespace: 192 bytes
          NET: Registered protocol family 16
          Blackfin GPIO Controller
          Blackfin DMA Controller
          stamp_init(): registering device resources
          NET: Registered protocol family 2
          IP route cache hash table entries: 1024 (order: 0, 4096 bytes)
          TCP established hash table entries: 2048 (order: 2, 16384 bytes)
          TCP bind hash table entries: 2048 (order: 1, 8192 bytes)
          TCP: Hash tables configured (established 2048 bind 2048)
          TCP reno registered
          NET: Registered protocol family 1
          JFFS2 version 2.2. (NAND) © 2001-2006 Red Hat, Inc.
          msgmni has been set to 122
          io scheduler noop registered (default)
          simple-gpio: now handling 48 GPIOs: 0 - 47
          Serial: Blackfin serial driver
          bfin-uart.1: ttyBF0 at MMIO 0xffc00400 (irq = 18) is a BFIN-UART
          bfin_mac_mdio: probed
          bfin_mac: attached PHY driver [Generic PHY] (mii_bus:phy_addr=0:01, irq=-1, mdc_clk=2500000Hz(mdc_div=25)@sclk=131MHz)
          bfin_mac bfin_mac.0: Blackfin on-chip Ethernet MAC driver, Version 1.1
          mtd_dataflash spi0.1: at45db321d (4096 KBytes) pagesize 512 bytes, erasesize 4096 bytes
          Creating 3 MTD partitions on “SPI Dataflash”:
          0x00000000-0x00040000 : “bootloader(spi)”
          0x00040000-0x00120000 : “linux kernel(spi)”
          0x00120000-0x00400000 : “file system(spi)“
          bfin-spi bfin-spi.0: Blackfin BF5xx on-chip SPI Controller Driver, Version 1.0, regs_base@ffc00500, dma channel@7
          rtc-bfin rtc-bfin: rtc core: registered rtc-bfin as rtc0
          bfin-wdt: initialized: timeout=20 sec (nowayout=0)
          TCP cubic registered
          NET: Registered protocol family 17
          rtc-bfin rtc-bfin: setting system clock to 1970-01-01 21:06:10 UTC (75970)
          JFFS2 write-buffering enabled buffer (512) erasesize (8192)
          VFS: Mounted root (jffs2 filesystem).
          Freeing unused kernel memory: 76k freed
          dma_alloc_init: dma_page @ 0x0013a000 - 256 pages at 0x03f00000
          

          Conclusion

          Loading compressed kernel (vmImage) or kernel+initrd (uImage) in u-boot from SPI flash is fast. However accessing SPI flash backed JFFS2 file systems in the kernel tends to be slow.

          Therefore it is recommendable loading a kernel image with an attached Initial RAM Disk(initrd).

          Then mount a JFFS2 file system (from your rc script), holding files that needs to be preserved during reboots, of files that are not frequently accessed. (Sacrifice runtime memory usage for boot speed.)
          Use RamFS or TmpFS File systems for temporary files not needed after a reboot.

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