Technical Note 36121
Absolute placement (v.5.xx) (in C source)
EW targets: ARM
EW component: C/C++ compiler
Keywords: "@" / #pragma locate, absolute address
Last update: February 17, 2009
Background - general
There are major changes in the EWARM between version 4.x and version 5.x. The link to the right gives some more information.
Background - specific
Absolute placement of constants are no longer allowed:
int const a @ 102030;
Problem
There is no way of express the above in an output file in the elf/dwarf format.
Solution 1 - (if you must use const)
The solution consists of two changes.
In the .c file place the variable in a named segment. In the .icf (for the linker) place the segment at a specific location.
The C source can have looked like this in 4.xx:
const char RELEASEDATE[16] @ 0x0000FF10 = __DATE__ ;
const char RELEASETIME[16] @ 0x0000FF20 = __TIME__ ;
This will be changed to this in the .c file in 5.xx:
#pragma location = "ConstSection1"
__root const char RELEASEDATE[16] = __DATE__ ;
#pragma location = "ConstSection2"
__root const char RELEASETIME[16] = __TIME__ ;
In the .icf file are these lines added:
place at address mem: 0x0000FF10 { readonly section ConstSection1 };
place at address mem: 0x0000FF20 { readonly section ConstSection2 };
The Ilink will then place the sections ConstSection1 at address 0x0000FF10, and the section ConstSection2 is placed at address 0x0000FF20.
Solution 2 - (if you dare not to use const)
The solution consists of a change from..
int const a @ 102030;
...to...
int a @ 102030;
...the drawback of this solution is that you disable the ICCARM which make checks for "do not write to const object". So this solution can lead to run-time errors.
Migration
It is also highly recommended that you have a look at the "The migration process" in the above guide. This will give you a good picture of what has to be done to migrate from version 4 to version 5 of the ARM IAR Embedded Workbench.
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