C251: PROBLEMS INITIALIZING ABSOLUTELY LOCATED VARIABLES

Information in this article applies to:

• C251 Version 2.14

QUESTION

I declared two global variables in file main.c as follows:

unsigned char near x _at_ 0x2000 = 5;
unsigned char near y _at_ 0x3000 = 10;

In the file main.h, I wrote:

extern unsigned char near x;
extern unsigned char near y _at_ 0x3000;

main.h is included in main.c. On the map file generated, both x and y are not located at the desired locations. Why?

ANSWER

This only happens when you initialize a variable located with the _at_ keyword when declaring the variable and the extern is in the same scope as the declaration.

The solution is to arrange your project so that you do not have externs and declarations for the same variables in the same scope.

The best way to do this is:

1. Create a file called globals.c which includes the declarations of all your global variables.
2. Create a file called globals.h which includes all the externs for your global variables.
3. Include the file globals.h in every source file except globals.c. Include globals.c in your project.

MORE INFORMATION

• Refer to The _at_ Keyword in the Cx51 User's Guide.

Last Reviewed: Friday, July 15, 2005