[U-Boot] Mips, U-Boot and ramdisk

[Detlev Zundel]

Hi Robert,

> Can anybody help me? I'm working on this for a few days...
>
> I'm working on a custom developed board, with Au1200, and I'd like to 
> use the U-Boot as bootloader. I ported the U-Boot to my board, made a 
> Linux kernel image, and a ramdisk image.
>
> To try out the configuration, I burn the U-Boot image into the flash (it 
> works well), and after I start the board, it download the kernel image 
> and the ramdisk image through TFTP. I'm using the following two commands:
>
> tftp 81000000 uImage
> tftp 81FFFFC0 uRamdisk
>
> I set the bootargs variable to: root=\dev\ram (I used: set bootargs 
> root=/dev/ram)

root=/dev/ram is definitely correct.  It was MS-DOS a while ago, which
switched the '/'s to '\'s on stealing the hierarchical file system
concept from Unix ;)

> But when I'm trying to start the Linux with the
>
> bootm 81000000 81FFFFC0
>
> the Linux can't find the ramdisk. It write out:
>
> Initrd not found or empty - disabling initrd
>
> But when I set its address into the bootargs (so the bootargs: 
> root=/dev/ram rd_start=0x82000000 rd_size=0x191160), it works well; it 
> successfully find the image, and can mount it.
>
> How does the U-Boot pass the ramdisk information? 

This is highly specific to the architecture.  Looking into MIPS code, it
an environment like datastructure is built and passes that to the kernel
(lib_mips/bootm.c).

> It sets some kind of environment variables in the bootm.c. 

Right, that's what I see also.

> But it doesn't work for me. Why?

I can't help you here, the best thing would be to debug this.  Maybe the
MIPS kernel changed the way the environment is passed?  

Cheers
  Detlev

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