Latest revision as of 14:43, 26 June 2015

u-boot

This page is only for kernel older than 2.6.26, for newer kernels, see Hardware/ARMEBS/3/u-boot

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 Hardware/ARMEBS/3/AutoUpdate 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 zImage.img will build this image for you.

Automatic startup bootcmd

At boot, u-boot do 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 (zImage.img) 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 zImage.img ; bootm 0x21000000"
 save

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

• the kernel image (zImage.img) 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 zImage.img ; 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 intance)
• 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 zImage.img ; 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

give 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, and it's possible to

• 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 intsance cp.b 0x21000000 0x10060000 0x200000 for copying 0x20000 byte from 0x21000000 (SDRAM) to 0x10060000 (flash)

u-boot works with environment variable for storing configuration option, 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)

 saveenv
 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.

• boot-delay

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

*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

• checkout the sources from https://svn.hevs.ch/svn/uit/armebs3/u-boot/trunk

 cd /opt/armebs3
 /opt/armebs3 snv 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 [source:/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 [source:/u-boot/trunk/cpu/arm920t/cpu.c u-boot/cpu/arm920t/cpu.c]
        • basic board dependent setup board_init [source:/u-boot/trunk/board/armebs3/armebs3.c u-boot/board/armebs3/armebs3.c]
        • set up exceptions interrupt_init [source:/u-boot/trunk/cpu/arm920t/at91rm9200/interrupts.c u-boot/cpu/arm920t/at91rm9200/interrupts.c]
        • initialize environment env_init [source:/u-boot/trunk/common/env_flash.c u-boot/common/env_flash.c]
        • initialze baudrate settings init_baudrate [source:/u-boot/trunk/lib_arm/board.c u-boot/lib_arm/board.c]
        • serial communications setup serial_init [source:/u-boot/trunk/cpu/arm920t/at91rm9200/serial.c u-boot/cpu/arm920t/at91rm9200/serial.c]
        • stage 1 init of console console_init_f [source:/u-boot/trunk/board/armebs3/armebs3.c u-boot/board/armebs3/armebs3.c]
        • say that we are here display_banner [source:/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) [source:/u-boot/trunk/board/armebs3/armebs3.c u-boot/board/armebs3/armebs3.c]
        • display dram info display_dram_config [source:/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: [1].