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====== Making it easy for u-boot to find uImage and uinitrd ======
I often fiddle with testing root images, kernels and initrd on my kirkwood based systems by using usb flash sticks. I found that although Jeff did a brilliant job on uboot, at the time I started fiddling with custom boot images on my dosckstar, his default environment was unable to directly boot all my testing images that were rapidly changing in layout. To work around this I started making canges to his environment.

I made myself a custom environment that was more flexible and allowed me to boot from any usb port as long as the following limitations are met:
  * the kernel must be called uImage or must be linked with that name
  * the initrd must be called uinitrd or must be linked with that name
  * uImage and uinitrd must be contained in the first 4 detected usb devices
  * uImage and uinitrd must be in the root or in a boot sub-directory in the device that holds them
  * the root filesystem bust be labelled "root" and should possibly be ext3 formatted

Heres the environment dumped from fw_printenv: (taken from my GoFlexNet)

  arcNumber=<put here your device's correct arcNumber>
  baudrate=115200
  boot_flash_kernel=nand read $flash_kernel_load_addr $flash_kernel_offest $flash_kernel_size; bootm $flash_kernel_load_addr
  bootargs=console=ttyS0,115200 mtdparts=orion_nand:1M(u-boot),4M(uImage),32M(rootfs),-(data) root=/dev/sda2 ro rootfstype=ext2
  bootcmd=run usb_scan; run set_flash_bootargs; run boot_flash_kernel
  bootdelay=3
  console=console=ttyS0,115200
  ethact=egiga0
  ethaddr=<put here your mac address>
  flash_kernel_load_addr=0x6400000
  flash_kernel_offest=0x100000
  flash_kernel_size=0x300000
  flash_root_fs=root=/dev/mtdblock2
  flash_root_fstype=rootfstype=jffs2
  led_error=orange blinking
  led_exit=green off
  led_init=green blinking
  mainlineLinux=yes
  mtdids=nand0=orion_nand
  mtdparts=mtdparts=orion_nand:1M(u-boot),4M(uImage),32M(rootfs),-(data)
  partition=nand0,2
  root_fs=root=LABEL=root
  rootfstype=rootfs=ext3
  sb_scan_1=usb=0:2 dev=sda2
  set_flash_bootargs=setenv bootargs ${console} ${mtdparts} ${flash_root_fs} ro ${flash_root_fstype}
  set_usb_bootargs=setenv bootargs ${console} ${mtdparts} ${root_fs} ro ${root_fstype}
  stderr=serial
  stdin=serial
  stdout=serial
  usb_boot_6=setenv root_fs root=/dev/sdg${usb_dev_part}
  usb_dev_list=3 2 1 0
  usb_dev_part=1
  usb_part_list=4 3 2 1
  usb_scan=usb start; setenv usb_boot_dev none; for dev in  $usb_dev_list; do test $dev -eq 0 && setenv devname /dev/sda ; test $dev -eq 1 &&  setenv devname /dev/sdb ; test $dev -eq 2 && setenv devname /dev/sdc ; test $dev -eq 3 && setenv devname /dev/sdd ; echo $devname ; for part in $usb_part_list; do echo $dev $part ; if ext2load usb ${dev}:$part 0x800000 /boot/uImage 10 ; then setenv usb_boot_dev $dev:$part ; setenv usb_boot_dir /boot ; fi  ; if ext2load usb ${dev}:$part 0x800000 /uImage 10 ; then setenv usb_boot_dev $dev:$part ; setenv usb_boot_dir ; fi  ; done; done; if test "$usb_boot_dev" = "none" ; then echo "No USB bootable device found" ; else echo "USB device $usb_boot_dev is bootable" ; setenv bootargs $console $mtdparts $root_fs ro $rootfstype ; echo $bootargs ; sleep 1; ext2load usb $usb_boot_dev 0x800000 $usb_boot_dir/uImage && setenv usb_boot_address 0x800000 ; ext2load usb $usb_boot_dev 0x1100000 $usb_boot_dir/uinitrd && setenv usb_boot_address 0x800000 0x1100000 ; bootm $usb_boot_address ; fi;


Labeling the root filesystem was a workaround when I started getting issues on device namings changes as I began using the SATA drives for NAS storage. In practice what was happening was that uboot thought that root was on sda but once the kernel booted it would detect the SATA drives before that and name the usb memory stick to after the last SATA drive causing a kernel panic as initrd attempts to mount the root filesystem.
I thus changed the u-boot environment to pass the root device as a label rather then a device path. This allows me to boot my GoFlexNet correctly from any usb stick (even trough a usb hub) regardless of the presence of the SATA drives.

To my understanding the latest uboot environments actually do more then this now ... so here's my last hybrid environment:

  arcNumber=3089
  baudrate=115200
  bifsload=0x800000 /boot/$kernel && ubifsload 0x1100000 /boot/$initrd; then bootm 0x800000 0x1100000; fi
  bootargs=${console} ${mtdparts} ${root_fs} ro ${rootfstype}
  bootcmd=usb start; run force_rescue_bootcmd; run ubifs_bootcmd; run usb_scan; usb stop; run rescue_bootcmd; run pogo_bootcmd; reset
  bootdelay=3
  console=ttyS0,115200
  ethact=egiga0
  ethaddr=xx:xx:xx:xx:xx:xx
  force_rescue=0
  force_rescue_bootcmd=if test $force_rescue -eq 1 || ext2load usb 0:1 0x1700000 /rescueme 1 || fatload usb 0:1 0x1700000 /rescueme.txt 1; then run rescue_bootcmd; fi
  initrd=uinitrd
  kernel=uImage
  led_error=orange blinking
  led_exit=green off
  led_init=green blinking
  mainlineLinux=yes
  mtdids=nand0=orion_nand
  mtdparts=mtdparts=orion_nand:1M(u-boot),4M(uImage),32M(rootfs),-(data)
  partition=nand0,2
  pogo_bootcmd=if fsload uboot-original-mtd0.kwb; then go 0x800200; fi
  rescue_bootcmd=if test $rescue_installed -eq 1; then run rescue_set_bootargs; nand read.e 0x800000 0x100000 0x400000; bootm 0x800000; else run pogo_bootcmd; fi
  rescue_installed=0
  rescue_set_bootargs=setenv bootargs console=$console ubi.mtd=2 root=ubi0:rootfs ro rootfstype=ubifs $mtdparts $rescue_custom_params
  root_fs=root=LABEL=root
  rootfstype=rootfs=ext3
  safearcNumber=2097
  setbootargs=setenv bootargs console=${console} ${mtdparts} ${root_fs} ro ${rootfstype}
  stderr=serial
  stdin=serial
  stdout=serial
  ubifs_bootcmd=run ubifs_set_bootargs; if ubi part data && ubifsmount rootfs && ubifsload 0x800000 /boot/uImage && ubifsload 0x1100000 /boot/uInitrd; then bootm 0x800000 0x1100000; fi
  ubifs_mtd=3
  ubifs_set_bootargs=setenv bootargs console=$console ubi.mtd=$ubifs_mtd root=ubi0:rootfs rootfstype=ubifs $mtdparts $ubifs_custom_params
  usb_dev_list=3 2 1 0
  usb_part_list=4 3 2 1
  usb_rootdelay=10
  usb_scan=sleep 5; setenv usb_boot_dev none; for dev in $usb_dev_list; do for part in $usb_part_list; do if ext2load usb ${dev}:$part 0x800000 /boot/$kernel 10; then setenv usb_boot_dev $dev:$part; setenv usb_boot_dir /boot; fi; if ext2load usb ${dev}:$part 0x800000 /$kernel 10; then setenv usb_boot_dev $dev:$part; setenv usb_boot_dir ; fi; done; done; if test "$usb_boot_dev" = "none"; then echo "No USB bootable device found"; else echo "USB device $usb_boot_dev is bootable"; run setbootargs; echo $bootargs; sleep 1; ext2load usb $usb_boot_dev 0x800000 $usb_boot_dir/$kernel && setenv usb_boot_address 0x800000; ext2load usb $usb_boot_dev 0x1100000 $usb_boot_dir/$initrd && setenv usb_boot_address 0x800000 0x1100000; bootm $usb_boot_address; fi;

====== Sources ======
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