Re: [avr-gcc-list] specific SRAM locations.

[Ned Konz]

On Apr 8, 2006, at 1:56 PM, Dave Lamont wrote:
> I need to allocate specific SRAM locations to some global  
> variables. The quantities
> in these reserved SRAM locations are passed from the microprocessor  
> back to a
> computer.
>
> My previous compiler allowed me to specify as follows
>
> int sat_bearing @0x180;
>
> or
>
> struct x {int a;
>             char c;
>             } alfa @0x185;

That's not Standard C, but there are at least three ways that I can  
think of that you can do this:

* Do what the avr-libc folks do, and make the name a #define for an  
anonymous object (what in C++ would be referred to as a "reference"):

#define sat_bearing (*(int *)(void*)(0x180))
#define alfa (*(struct x*)(void*)(0x185))

then you can say things like:

sat_bearing = 30;
alfa.c = 'f';

* Use a custom linker script that specifies these locations  
explicitly, and use an "extern" statement in C:

(linker)
alfa = 0x800185;
sat_bearing = 0x800180;

(c)
extern int sat_bearing;
extern struct x alfa;

* use a custom linker script that names the interesting sections and  
use the GDB attribute((__section__)) on the variables. I forget the  
exact syntax for this, but you basically just have fixed-address  
sections (defined inside the SECTION directive in your linker  
definition file) that you then use to refer to from C:

int sat_bearing __attribute__((__section__=myAttribute));



--
Ned Konz
MetaMagix embedded consulting
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