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Using two types of memory on a board

Posted on 2011-02-15
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Last Modified: 2012-05-11
I'm programming an embedded system using a custom board that has two types of memory on the board, 2MB of SRAM and 128 MB of SDRAM.

My operating system and application have broken the 2MB limit and so I need to start using the SDRAM too.  I have some large data structures that if I could just get those into SDRAM it would probably solve the problem.

I know the address for both types of memory.  How do I get my data structures to be store in the SDRAM?

Thanks.
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Question by:JohnSantaFe
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7 Comments
 

Author Comment

by:JohnSantaFe
ID: 34902667
As a follow up, I found that there is a gcc option to define where the text is located.  I could run my entire application out of SDRAM.  That would be ok too.

Anybody know how to use the gcc option to do that?

Thanks.
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LVL 12

Expert Comment

by:HappyCactus
ID: 34904499
Not gcc but maybe the linker.
But it depends on the platform and SDK - this is usually a customized feature.
what are you using?

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Author Comment

by:JohnSantaFe
ID: 34911911
I'm using a Sparc 8 based processor called a Leon3.  
I thought this was a standard feature of the linker that comes with GCC?
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LVL 12

Accepted Solution

by:
HappyCactus earned 1500 total points
ID: 34914131
You need to change the linker script. The linker script is a file that defines the memory layout used for the program.
According to the documentation (see: memory organization), the default linker script defines a .text segment starting at address 0x40000000.
According to this post, you can change the linker script directly from your project directory, by using the "-X" and "-T" options in bcc.
I do not have any way to check if this works.

Hope that helps.
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Author Closing Comment

by:JohnSantaFe
ID: 34931306
Kind of worked still getting strange behavior.
Thanks
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LVL 12

Expert Comment

by:HappyCactus
ID: 34932305
Which kind of "strange behaviour", related to this question (my comment doesn't solve this issue, that's why it's only "B" rated?) ? can you open a new question?
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Author Comment

by:JohnSantaFe
ID: 34948595
I appreciate the help.  
With your suggestions the linker would relocate the text but it would still not run. Eventually I figured out that on this architecture you also have to set the stack pointer to the top of the SDRAM for this to work.  Also I found that there is a more direct way to get the linker to relocate.  Instead of modifying the linker script you can just use -Wl -Ttext 0x60000000 in the call to the linker script.  
With those issues and a meaningful response taking two days, I didn't feel this deserved an "A".
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