Re: possible to have some C variables uninitiialized?

[Hans - Dulimarta <dulimart at egr dot msu dot edu>]

On Tue, 18 Jan 2000, Scott A Sumner wrote:

> Date: Tue, 18 Jan 2000 18:44:33 -0500
> From: Scott A Sumner <sasumner@juno.com>
> To: crossgcc@sourceware.cygnus.com, ColdFire@WildRice.com
> Subject: possible to have some C variables uninitiialized?
> 
> I'm using gcc on a 68000-based embedded system that has some normal RAM
> and some battery-backed RAM.  I'd like to know if there is a way to have
> the gcc compiler/linker not initialize certain C variables that will be
> located in the battery-backed RAM area.
>

One way that I can think of is to put those variables in a separate
section, say ".uninit", and then put the '(NOLOAD)' option for this
section in your linker script. By doing this, the linker will compute the
correct relocation address without loading the section into the
battery-backed RAM.

The following template of linker script may help you:

...

MEMORY {
   NormalRAM: ORIGIN = ....., LENGTH = ....
   BattRAM  : ORIGIN = ....., LENGTH = ....
}

SECTIONS {
  ... other sections [.text, .data. ,bss, ....] here
  
   .uninit (NOLOAD) : { ...... } >BattRAM
}

....



> I'd like these global variables to be declared normally, for
example, > 
> int IAmANonVolatileInt = 3;
> 
> but I don't want them lumped in with the normal global variables that
> will get initialized to either 0 or to a certain value on powerup of the
> embedded system.
> 
> I could cheat and do the following:
> 
> #define BATTERY_BACKED_RAM_ADDRESS (0x800000)
> #define IAmANonVolatileInt (*(int *)BATTERY_BACKED_RAM_ADDRESS)
> 
> but I'd rather not.
> 
> 
> Any ideas on how to accomplish this?  An example would be great, too!
> 
> ------
> Want more information?  See the CrossGCC FAQ, http://www.objsw.com/CrossGCC/
> Want to unsubscribe? Send a note to crossgcc-unsubscribe@sourceware.cygnus.com
> 

-- 
Hans Dulimarta, Ph.D.        dulimart@[egr.msu.edu, computer.org]
                                 http://www.egr.msu.edu/~dulimart 
Visiting Research Associate,  Electrical & Computer Engineering
Michigan State University, East Lansing, MI 48824, (517) 432-7589


------
Want more information?  See the CrossGCC FAQ, http://www.objsw.com/CrossGCC/
Want to unsubscribe? Send a note to crossgcc-unsubscribe@sourceware.cygnus.com