[arm-gnu] Placing variable at absolute address in RAM

[JM]

The only reason I mentioned about GCC not making it easy is that apparently at least one compiler makes it easy.  I'm so jealous!


With the RealView ARM C Compiler, you may use either pointer definitions (as shown above) or __attribute__((at(address))) keyword to define a variable at a fixed memory address. In contrast to 
the pointer construct, the following definition also makes a correct 
memory reservation, so that the area cannot be used twice.
int var __attribute__((at(0x40001000)));


________________________________
 From: 42Bastian <list-bastian.schick at sciopta.com>
To: arm-gnu at codesourcery.com 
Sent: Thursday, April 5, 2012 10:23 AM
Subject: Re: [arm-gnu] Placing variable at absolute address in RAM
 

> I had no idea this would be so difficult, but apparently GCC doesn't
> make this easy, unlike other compilers.  Since I'm using the lite
> (free) compiler, buying one really isn't an option for hobby use.

The problem is complicated. GCC makes it as easy as other compilers to
place a variable somewhere.
Your constraints (not wasting RAM) makes is complicated.

Try (untested):

    . = ALIGN(1024);
    dma_ring = .;
    /* place some data here e.g.*/
    test.o(.data .bss)
    toto.o(.data .bss)
    dma_eof_data = .;
    dma_desc = dma_ring+464;
    . = dma_desc+16;
    /* place more stuff */

Check the map file, that dma_desc is >= dma_eof_data.

-- 
42Bastian
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