Lpc2000

On Thursday 10 November 2005 05:26, Tom Walsh wrote:
> szemzoandras wrote:
> >Hello,
> >
> >
> >Is it possible to place a variable to a fixed memory location in gcc,
> >like in keil, i mean:
> >
> >unsigned int dd _at_ 0x81000000;
>
> FWIW, I wonder why Keil added an extension to their C compiler?  I've
> been using "int * dd = ((unsigned int *)0x81000000)" for many many
> years.  Not only with gcc, but other compilers as well.

There is a difference.

When you do something like:
unsigned int dd _at_ 0x810000;

often the linker will check for overlaps etc. Depends on the compiler/linker 
though.

Also, you need to look at the their offerings to understand it. Their older 
compilers (8051 etc) had this feature and so did PLM (now that was a 
fantastic language for 8051s)! They don't want to make their newer compilers 
seem less capable.

When you do 
int * dd = ((unsigned int *)0x81000000
you're bypassing everything. That's probably fine for accessing hard locations 
like peripherals etc.

IMHO, using extensions is a very bad thing. It was OK in the days of 8-bitters 
where "C" code was just a C representation of assembly and code was very 
non-portable. With most code though, you need portability. Heck I still use 
code I first wrote 15 years ago and have been dragging from project to 
project. Using any non-standard things breaks portability.

I prefer to not do any of this sort of thing (except for hardware-specified 
stuff like peripherals) and instead use linker scripts to do any placement.