[U-Boot] Loading and Running u-boot from context RAM

[Stefan Roese]

Hi Ronny,

On Wednesday 31 March 2010 07:16:33 Ronny D wrote:
> I am working on PPC440 based customized board having 4MB context ram.
> 
> what are all changes need to perform to skip relocation of u-boot in DDR
> and relocated it to context ram and run from the same location.

I'm not sure if I understand your question correctly. Are you looking for a 
way to skip the SDRAM initialisation and relocation from FLASH to SDRAM and 
directly "jump" to the U-Boot code already located somewhere in RAM? If yes, 
then you should take a look at the Sequoia (440EPx) ramboot build target. Here 
the commit log from the base support patch:

    ppc4xx: Add Sequoia RAM-booting target
    
    This patch adds another build target for the AMCC Sequoia PPC440EPx
    eval board. This RAM-booting version is targeted for boards without
    NOR FLASH (NAND booting) which need a possibility to initially
    program their NAND FLASH. Using a JTAG debugger (e.g. BDI2000/3000)
    configured to setup the SDRAM, this debugger can load this RAM-
    booting image to the target address in SDRAM (in this case 0x1000000)
    and start it there. Then U-Boot's standard NAND commands can be
    used to program the NAND FLASH (e.g. "nand write ...").
    
    Here the commands to load and start this image from the BDI2000:
    
    440EPX>reset halt
    440EPX>load 0x1000000 /tftpboot/sequoia/u-boot.bin
    440EPX>go 0x1000000
    
    Please note that this image automatically scans for an already
    initialized SDRAM TLB (detected by EPN=0). This TLB will not be
    cleared. This TLB doesn't need to be TLB #0, this RAM-booting
    version will detect it and preserve it. So booting via BDI2000
    will work and booting with a complete different TLB init via
    U-Boot works as well.

Hope this helps.

Cheers,
Stefan

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