Re: [ECOS] Which is correct start address with romram modewithpowerpc 8245 ?? 0x0 or 0xfff00100??

[Gary Thomas <gary at mlbassoc dot com>]

On Fri, 2005-08-12 at 09:52 +0800, Steven_cheng wrote:
> Dear Thomas,
> 
>     Thank you for your reply~~
>     I have one question about the vector address with different startup 
> mode. I think the bootup procedure of the ROMRAM is similar to the 
> ROM, it should bootup from ROM address, so the vector address of 
> the ROMRAM should be the same with ROM.
> 
> In other words, the ROM and ROMRAM should bootup from ROM
> address.  Is it correct ??
> 
> But I find that the vector adderss are different in ROM/ROMRAM/RAM
> with Cogent csb281 images.
> 
> StarupMode |  Vector Address | Reset Vector Address
> ---------------------------------------------------------------
> ROM            |    0xFFF00000   |   0xFFF00100
> ROMRAM   |    0x0                  |   0x100
> RAM            |    0x0                  |   0x100
> 
> The ROMRAM vectort address is the same with the RAM. Is is correct ??

Do you understand how the "start from RESET" works on this platform?
Try reading the documentation (hardware manuals) and you'll see that
after RESET, *ALL* addresses map only onto the FLASH, so it doesn't
really matter what address the ROMRAM version is linked at. It starts
executing, just like the ROM version, at 0x100 into the code.  The
next thing that gets done is to set up the hardware to actually be
able to access the RAM, etc.  Once this is done, the code is copied 
from the FLASH (aka ROM) to RAM and then execution continues from 
that RAM location.  Thus the code needs to be linked at RAM addresses
even though it starts out life in ROM (hence the ROMRAM moniker)

In the case of the ROM version, it actually executes from the ROM
(FLASH), so it must be linked to those addresses.

-- 
------------------------------------------------------------
Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
------------------------------------------------------------


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