U-Boot Overview

Offical website
- git
- FTP
Boot Linux Kernel
- Boot from SD Card
- Boot over Network (Ethernet)
U-Boot Commands
U-Boot Environment Variables
U-Boot Scripting Capabilities
Misc
- examine the boot arguments
Further Reading

Offical website

http://www.denx.de/wiki/U-Boot/WebHome

git

http://www.denx.de/cgi-bin/gitweb.cgi?p=u-boot.git;a=summary

FTP

ftp://ftp.denx.de/pub/u-boot/

Boot Linux Kernel

Boot from SD Card

TI8168_EVM# mmc rescan 0
TI8168_EVM# fatload mmc 0 0x81000000 uImage
TI8168_EVM# setenv bootargs 'console=ttyO0,115200n8 root=/dev/mmcblk0p2 mem=128M rootwait'
TI8168_EVM# bootm 0x81000000

Boot over Network (Ethernet)

Overview

When kernel image and ramdisk image are fetched from a tftp server:

Ensure that the EVM is connected to network with DHCP and TFTP server set up
Set 'ethaddr' U-Boot environment variable with proper ethernet address in format 'xx:xx:xx:xx:xx:xx' (replace 'xx' with proper hexadecimal values)
Copy kernel image and ramdisk to TFTP server's root directory.
Execute follwing commands at U-Boot prompt. We assume kernel image name as 'uImage' and ramdisk file name as 'ramdisk.gz'

Method1 (DHCP) for ramdisk,gz

TI8168_EVM# setenv autoload no
TI8168_EVM# dhcp
TI8168_EVM# setenv serverip <Server IP Address>
TI8168_EVM# tftp 0x81000000 uImage
TI8168_EVM# tftp 0x82000000 ramdisk.gz
TI8168_EVM# setenv bootargs 'mem=200M console=ttyO0,115200n8 root=/dev/ram0 initrd=0x82000000,40M ramdisk_size=45000 ip=dhcp'
TI8168_EVM# bootm 0x81000000

Method 2 for NFS Filesystem

root=/dev/nfs rw: the root filesystem will be mounted using NFS, and it will be writable.
nfsroot=192.168.1.1:/opt/eldk-4.2/ppc_4xx: the NFS server has the IP address 192.168.1.1, and exports the directory /opt/eldk-4.2/ppc_4xx for our system to use as root filesystem.
ip=192.168.100.6:192.168.1.1:192.168.1.1:255.255.0.0:canyonlands::off: the target has the IP address 192.168.100.6; the NFS server is 192.168.1.1; there is a gateway at IP address 192.168.1.1; the netmask is 255.255.0.0 and our hostname is canyonlands. The first ethernet interface (eth0) will be used, and the Linux kernel will immediately use this network configuration and not try to re-negotiate it (IP autoconfiguration is off).

static IP

Alternatively, kernel can be made to use the same IP address as assigned to U-Boot instead of doing DHCP request again by setting U-Boot parameters as follows:

TI8168_EVM# print ethaddr <-- Check if MAC address is assigned and is unique
TI8168_EVM# setenv ethaddr <unique-MAC-address> <-- Set only if not present already, format xx:yy:zz:aa:bb:cc
TI8168_EVM# setenv bootcmd 'dhcp;run addip; tftp 81000000 uImage;bootm'
TI8168_EVM# setenv hostname <unique-hostname>
TI8168_EVM# setenv addip 'setenv bootargs ${bootargs} ip=${ipaddr}:${nfsserver}:${gatewayip}:${netmask}:${hostname}:eth0:off'
TI8168_EVM# setenv autoload no
TI8168_EVM# setenv nfsserver <nfs-server-ip> <-- Make sure the same NFS server IP is used below
TI8168_EVM# setenv bootargs 'console=ttyO0,115200n8 root=/dev/nfs nfsroot=<nfs-server-ip>:<path-to-nfs-share>,nolock rw mem=128M'
TI8168_EVM# setenv serverip <tftp-server-ip>
TI8168_EVM# saveenv
TI8168_EVM# boot

DHCP

TI8168_EVM# print ethaddr <-- Check if MAC address is assigned and is unique
TI8168_EVM# setenv ethaddr <unique-MAC-address> <-- Set only if not present already, format uv:yy:zz:aa:bb:cc
TI8168_EVM# setenv bootcmd 'dhcp;tftp 81000000 uImage;bootm'
TI8168_EVM# setenv autoload no
TI8168_EVM# setenv nfsserver <NFS server-ip> <-- Make sure the same NFS server IP is used below
TI8168_EVM# setenv bootargs 'console=ttyO2,115200n8 root=/dev/nfs nfsroot=<NFS server-ip>:<NFS share>,nolock rw mem=128M ip=dhcp'
TI8168_EVM# setenv serverip <tftp-server-ip>
TI8168_EVM# saveenv
TI8168_EVM# boot

Example 1 (dhcp)

setenv bootdelay 4
setenv baudrate 115200
setenv bootargs console=ttyO0,115200n8 rootwait rw mem=364M@0x80000000 mem=324M@0x9F900000 vmalloc=500M notifyk.vpssm3_sva=0xBF900000 root=/dev/nfs nfsroot=143.89.147.79:/home/testbed/targetfs ip=dhcp
setenv bootcmd 'dhcp;setenv serverip 143.89.147.79;tftpboot;bootm'
setenv autoload no
setenv serverip 143.89.147.79
setenv bootfile uImage

Example 2 (static ip)

host PC

sudo  ifconfig eth0 10.2.1.10 netmask 255.255.255.0 up

ti816x board

setenv ipaddr 10.2.1.9
setenv serverip 10.2.1.10
setenv bootcmd 'tftpboot 0x81000000 uImage; bootm 0x81000000'
setenv autoload no
setenv bootargs 'mem=128M console=ttyO0,115200n8 root=/dev/nfs rw  nfsroot=10.2.1.10:/home/testbed/targetfs  ip=10.2.1.9:10.2.1.10:10.2.1.1:255.255.255.0::eth0:off'
boot

setenv bootargs 'console=ttyO0,115200n8 rootwait rw  mem=364M@0x80000000 mem=324M@0x9F900000 vmalloc=500M notifyk.vpssm3_sva=0xBF900000 root=/dev/nfs  nfsroot=10.2.1.10:/home/testbed/targetfs  ip=10.2.1.9:10.2.1.10:10.2.1.1:255.255.255.0::eth0:off'

U-Boot Commands

bdinfo - print Board Info structure

The bdinfo command (short: bdi) prints the information that U-Boot passes about the board such as memory addresses and sizes, clock frequencies, MAC address, etc. This information is mainly needed to be passed to the Linux kernel.

=> bdi
memstart    = 0x00000000
memsize       = 0x20000000
flashstart  = 0xFC000000
flashsize   = 0x04000000
flashoffset = 0x00000000
sramstart   = 0x00000000
sramsize    = 0x00000000
bootflags   = 0xFFFE6530
...

md - memory display

md - memory display

Usage:
md [.b, .w, .l] address [# of objects]

The md can be used to display memory contents both as hexadecimal and ASCII data.

=> md 0x100000
00100000: 8083764e bd86200a 60a19054 2c12c402    ..vN.. .`..T,...
00100010: c101d028 00438198 7ab01239 62406128    ...(.C..z..9b@a(
00100020: 0c900d05 320b4581 1ca3d0a2 c498293a    ....2.E.......):

mm - memory modify (auto-incrementing)

mm - memory modify (auto-incrementing address)

Usage:
mm [.b, .w, .l] address

mtest

mtest <start-address> <end-address> <test pattern> <# of iterations>

Example

Target# mtest 0x80000000 0xA0000000 0xaa55aa55 3 (referred as Test A)
Target# mtest 0xA0000000 0xC0000000 0xaa55aa55 3 (referred as Test B)

List files on a FAT32 formated SD card

TI8168_EVM# mmc rescan 0
TI8168_EVM# fatls mmc 0

Set static ip

TI8168_EVM# setenv ipaddr <your static ip>

U-Boot Environment Variables

`bootargs`

bootargs: The contents of this variable are passed to the Linux kernel as boot arguments (aka "command line").

`bootcmd`

bootcmd: This variable defines a command string that is automatically executed when the initial countdown is not interrupted. This command is only executed when the variable bootdelay is also defined!

`ethaddr`

ethaddr: Ethernet MAC address for first/only ethernet interface (= eth0 in Linux). This variable can be set only once (usually during manufacturing of the board). U-Boot refuses to delete or overwrite this variable once it has been set.

`serverip`

serverip: TFTP server IP address; needed for tftp command.

U-Boot Scripting Capabilities

$ mkimage -A arm -O linux -T script -C none -a 0 -e 0 -n "boot" -d boot.cmd boot.scr

Misc

examine the boot arguments

Note: Once your system is up and running, if you have a simple shell login, you can normally examine the boot arguments that were used by the kernel for the most recent boot with the command:

$ cat /proc/cmdline