Hardware/ARMEBS/3/u-boot

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u-boot

for Linux < 2.6.26 see : u-boot before 2.6.26

u-boot is a bootloader, we've choosen it because it supports usb and network operations.

It has been adapted to support our board, especially an auto-update function, using an USB flash drive.

As any bootloader, u-boot can be used (and this is it's main purpose) to start another program (or operating system), for instance Linux. The application we want to run must be in a special form called image and can be generated using mkimage (in u-boot/tools/), for instance generating a Linux kernel image is done using the following command :

 mkimage -A ARM -T kernel -C none -O Linux -a 0x20008000 -d /opt/armebs3/linux-2.6.15/output/arch/arm/boot/zImage linux.img

After r641 of our Linux kernel, make uImage will build this image for you.

Automatic startup bootcmd

At boot, u-boot does this:

  • By default, it runs the command in the bootcmd variable.
  • If the first button (S1 on the ARMEBS3) is pressed, it tries to do AutoUpdate on the USB key. If it fails, it runs bootcmd}.
  • If the third button (S3 on the ARMEBS3) is pressed, it jumps to 0x10060000, after disabling instruction cache.

Settings for the technical informatics laboratories

The instruction cache must be shut-down before downloading a software via the JTAG interface.

 set bootcmd icache off
 save


Get the Linux kernel from tftp (using a static ip address), and launch it

  • the kernel image (uImage) is at the root of the tftp server
  • the tftp server IP is 153.109.5.233
  • the armebs3 IP is 153.109.5.232
  • don't forget to set the LinuxCommandLine in the bootargs variable
 set ipaddr 153.109.5.232
 set serverip 153.109.5.233
 setenv bootcmd "tftpboot 0x21000000 uImage ; bootm 0x21000000"
 save


Get the Linux kernel from tftp (using DHCP), and launch it

  • the kernel image (uImage) is at the root of the tftp server
  • the tftp server IP is 153.109.5.233
  • don't forget to set the LinuxCommandLine in the {{{bootargs}}} variable
 set serverip 153.109.5.233 
 setenv bootcmd "bootp 0x21000000 uImage ; bootm 0x21000000"
 save


Get the Linux kernel from flash, and launch it

  • The kernel image is supposed to be flashed at 0x10060000
  • Download the kernel to ram (using tftp for instance)
  • Flash it
 erase 0x10060000 +0x200000
 cp.b 0x21000000 0x10060000 0x200000
  • don't forget to set the LinuxCommandLine in the bootargs variable
 setenv bootcmd "bootm 0x10060000"
 save


Get the Linux kernel from an USB key, and launch it

  • The USB key must be FAT16 formated, without partitions
  • don't forget to set the LinuxCommandLine in the bootargs variable
 set bootcmd "usb start ; fatload usb 0 0x21000000 uImage ; bootm 0x21000000"


Configuration

The first time you start u-boot there are some things to configure.

Connect with a terminal emulator on the first serial port (115200,8,n,1).


Basic commands

here is a small list of usefull commands:

  • help : gives you help for built-in commands (without argument, display a list of all commands)
  • bmp : used to display a bmp on the screen (example: bmp 0x10f00000 will display the bitmap at address 0x10f00000). This command support standard bmp or gzipped bmp.
  • usb : used to manage usb for instance: usb start, then usb storage to see which storage has been attached.
  • fatload : load a file from a fat file system into memory, example : fatload usb 0 0x21000000 linux.img will load the linux kernel image at 0x21000000, don't forget to do usb start before that :-)
  • erase : erase flash, for instance erase 0x10060000 +0x200000 for erasing flash from 0x10060000 to 0x10260000
  • cp![.size] : copy from memory to memory (or to flash), for instance cp.b 0x21000000 0x10060000 0x200000 for copying 0x20000 byte from 0x21000000 (SDRAM) to 0x10060000 (flash)

u-boot works with environment variables for storing configuration options, and here are the basic commands for setting/reading variables:

  • setting a variable (v1)
 setenv toto hello world
 toto=hello world
  • printing a variable (v1)
 printenv toto
 toto=hello world
  • printing a variable (v2)
 echo ${toto}
 hello world
  • saving variables (to flash)
 save
 Saving Environment to Flash...
 Un-Protected 1 sectors
 Erasing Flash...
 . done
 Erased 1 sectors
 Writing to Flash... .
 done
 Protected 1 sectors

Well known variables

u-boot uses some known variables names for it's own use, here is an overview.

  • board (armebs3 specific) and protected* variable

name (type of the board), used to init board specific hardware. u-boot is compiled to support ALL ARMEBS3 based board and uses this variable to know which board it is running on. possible values are : armebs3, ipresenter, sidney, proto.

  • ethadd protected* variable

Ethernet address, MUST be set-up for boards using network, example : setenv ethaddr 00:00:17:00:00:00.

  • bootdelay

delay after reset before the bootcmp is run

  • bootcmd

command to run automatically after a reset, example : setenv bmp display 0x10f00000 \; bootm 0x10060000 to diplay the bitmap located at 0x10f00000 and run the software from 0x10060000. unset it (setenv bootcmd) to do nothing at boot.

  • bootargs ( see also [wiki:LinuxCommandLine linux command line])

boot arguments, passed to the application to be run (at least passed to linux as the kernel command line), example setenv bootargs root=1f03 ro rootfstype=romfs console=ttyS0,9600 video=s1d13x06fb:crt,mode:800x600-16

  • baudrate

The baudrate for the console

  • sdtin, stdout, stderr

Defines where the standard input, output and error stream are sent by u-boot, values can be : serial, vga (for the mezza_lcd and it's keyborard) and vga-serial (for both serial AND mezza_lcd).

  • video : Setup the vga output, values can be :
    • video=lcd,640x480-16 for the mezza_lcd + the laboratory LCD screen.
    • video=crt,800x600-16 for the mezza_lcd + vga output
    • video=lcd,320x240-16 for the sidney board.

*protected variables can only be set once. To reset this variables, the flash configuration area must be erased and the system rebooted (flash protect off all ; erase 0x10040000 + 0x20000 ; boot), then the protected variables can be set again.


compiling/installing

 cd /opt/armebs3
 /opt/armebs3 svn checkout https://svn.hevs.ch/svn/uit/armebs3/u-boot/trunk u-boot
  • compile it
 /opt/armebs3 cd u-boot
 /opt/armebs3/u-boot make armebs3_config
 /opt/armebs3/u-boot make
 /opt/armebs3/u-boot
  • flash it
 /opt/armebs3/u-boot cp u-boot.bin /opt/armebs3/tftp
 reset
 mm 0xfffffc20  0x0000ff01
 mm 0xffffff70  0x000030ff
 mm 0xfffffc30  0x00000001
 unlock 0x10000000 0x20000 2
 erase 0x10000000 0x20000 2
 Erasing flash at 0x10000000
 Erasing flash at 0x10020000
 Erasing flash passed
 prog 0x10000000 u-boot.bin bin
 Programming u-boot.bin , please wait ....
 Programming flash passed

u-boot, step by step, file by file

here is a small overview of what is done in which file

  • /u-boot/trunk/cpu/arm920t/start.S u-boot/cpu/arm920t/start.S
    • reset vectors -> reset
    • reset
      • do cpu init
      • call lowlevel_init from [source:/u-boot/trunk/cpu/arm920t/at91rm9200/lowlevel_init.S u-boot/cpu/arm920t/at91rm9200/lowlevel_init.S]
        • init sdram, chip select, ...
      • relocates to sdram, setup stack, clear bss section
      • jump to start_armboot (relocated)
    • start_armboot from /u-boot/trunk/lib_arm/board.c u-boot/cpu/arm920t/lib_arm/board.c
      • init global data sturcture (gd)
        • call every functions from the init_sequence[] table
          • basic cpu dependent setup cpu_init u-boot/trunk/cpu/arm920t/cpu.c u-boot/cpu/arm920t/cpu.c
          • basic board dependent setup board_init u-boot/trunk/board/armebs3/armebs3.c u-boot/board/armebs3/armebs3.c
          • set up exceptions interrupt_init /u-boot/trunk/cpu/arm920t/at91rm9200/interrupts.c u-boot/cpu/arm920t/at91rm9200/interrupts.c
          • initialize environment env_init /u-boot/trunk/common/env_flash.c u-boot/common/env_flash.c
          • initialze baudrate settings init_baudrate /u-boot/trunk/lib_arm/board.c u-boot/lib_arm/board.c
          • serial communications setup serial_init /u-boot/trunk/cpu/arm920t/at91rm9200/serial.c u-boot/cpu/arm920t/at91rm9200/serial.c
          • stage 1 init of console console_init_f /u-boot/trunk/board/armebs3/armebs3.c u-boot/board/armebs3/armebs3.c
          • say that we are here display_banner /u-boot/trunk/lib_arm/board.c u-boot/lib_arm/board.c
          • configure available RAM banks dram_init (only setup how many sdram is here for u-boot, no sdram initialization) /u-boot/trunk/board/armebs3/armebs3.c u-boot/board/armebs3/armebs3.c
          • display dram info display_dram_config /u-boot/trunk/lib_arm/board.c u-boot/lib_arm/board.c
          • ...
          • run u-boot

External link(s)

here is the u-boot home page: http://u-boot.sourceforge.net/.

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