[U-Boot] newbie questions regarding some config options.

[Christopher Harvey]

 On Mon, 13 Jun 2011 15:08:35 +0100, PHIL.EDWORTHY at renesas.com wrote:
> Hi Matthias,
>
>> >> What is the CONFIG_SYS_TEXT_BASE variable and how can
>> >>  I figure out what it should be?
>> >
>> > U-boot is typically stored in flash and one of the first things it 
>> does when executed is relocate to ram. CONFIG_SYS_TEXT_BASE is
>> > the relocation
>> > address. Typically, u-boot global data, heap and then stack is 
>> stored just below this.
>>
>> On ARM, CONFIG_SYS_TEXT_BASE is typically the base address of the 
>> image
>> in flash. This is, on a system booting from NOR, the address of the
>> first instruction which is fetched from the CPU.
>>
>> > Since u-boot is used to load some other program like the kernel, 
>> you need the u-boot relocation address to be out of the way of this. 
>> So, for the
>> > boards I have seen (not arm), CONFIG_SYS_TEXT_BASE is set to the 
>> top of ram - 256KB, i.e. enough room for the u-boot image.
>>
>> The relocation address is dynamically calculated from a couple of
>> (runtime) information and has nothing to do with 
>> CONFIG_SYS_TEXT_BASE.
>> This is true for ARM and AFAIK for PPC.
>
> Thanks for the additional info - SH is a little different then!
>
> Phil

 Thanks for the information. Since CONFIG_SYS_TEXT_BASE seems to be a 
 critical value and isn't something that can be ignored, maybe it 
 deserves an entry in the already helpful README. I'd write it myself but 
 I'm not qualified.

 -Chris