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Understanding U-boot environment variables

Posted by balanga 
Understanding U-boot environment variables
August 21, 2018 01:30AM
I often see displays of various environment variables but never pay much attention to them apart from a few specific ones, but I'd like to know if there is a definite reference for them and what they mean, or a guide to explain what they are used for.
Here is what I currently have on a Seagate GoFlex Home unit running the Stock version of Linux:-

baudrate=115200
loads_echo=0
ipaddr=169.254.254.253
serverip=169.254.254.254
rootpath=/mnt/ARM_FS/
netmask=255.255.0.0
run_diag=yes
console=console=ttyS0,115200
CASset=min
MALLOC_len=1
ethprime=egiga0
bootargs_end=:::DB88FXX81:eth0:none
image_name=uImage
standalone=fsload 0x2000000 $(image_name);setenv bootargs $(console) root=/dev/mtdblock0 rw ip=$(ipaddr):$(serverip)$(bootargs_end) $(mvPhoneConfig); bootm 0x2000000;
ethaddr=00:50:43:34:33:06
ethmtu=1500
usb0Mode=host
nandEcc=1bit
netretry=no
rcvrip=169.254.100.100
loadaddr=0x02000000
autoload=no
ethact=egiga0
stdin=serial
stdout=serial
stderr=serial
mainlineLinux=no
enaMonExt=no
enaCpuStream=no
enaWrAllo=no
pexMode=RC
disL2Cache=no
setL2CacheWT=yes
disL2Prefetch=yes
enaICPref=yes
enaDCPref=yes
sata_dma_mode=yes
netbsd_en=no
vxworks_en=no
bootdelay=3
disaMvPnp=no
enaAutoRecovery=yes
pcieTune=no
filesize=33AA2E
bootargs=console=ttyS0,115200 root=/dev/ram0 rw ramdisk=0x01100000,8M install_type=nand
bootargs_root=ubi.mtd=2,2048 root=ubi0:rootfs rootfstype=ubifs init=/linuxrc
console2=console=ttyS0,115200
bootcmd=nand read.e 0x800000 0x100000 0x600000; setenv bootargs $(console2) $(bootargs_root); bootm 0x800000
Re: Understanding U-boot environment variables
August 21, 2018 02:42AM
This is the official manual:
http://www.denx.de/wiki/DULG/UBootEnvVariables

It is, as usual for open source software, quite old.

-bodhi
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Re: Understanding U-boot environment variables
August 21, 2018 09:47AM
bodhi Wrote:
-------------------------------------------------------
> This is the official manual:
> http://www.denx.de/wiki/DULG/UBootEnvVariables
>
> It is, as usual for open source software, quite
> old.

Thanks, it's a start, but as it says:-

This section lists the most important environment variables,

and many are not mentioned. There must be some guide somewhere about how to use these variables, but I haven't found one yet.

One thing which strikes me is the IP adresses used...

ipaddr=169.254.254.253
serverip=169.254.254.254
rcvrip=169.254.100.100

I'm obviously missing something significant about the use of this subnet...
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