C51: EXTERN VARS AND INLINE ASSEMBLY

Information in this article applies to:

• C51 All Versions

QUESTION

I am using inline assembly. Included in the C file in which the inline assembly resides is a header file (.H) that contains EXTERN declarations for variables declared in other modules. When I try to build the project, I receive either UNDEFINED SYMBOL or REDEFINED SYMBOL errors pointing to the EXTERNS. Is there an example of the correct way to accomplish this?

ANSWER

Yes.

1. Create a project with the following files:

   
   MAIN.CM

     #pragma SRC(MAIN.A51)
     #include "xdatinc.h"
   
     void main(void) {
        ioport=0x55;
   
        while(1) {
          ioport+=2;
          #pragma asm
            inc r0  // this is just here to add inline asm to the mix..
          #pragma endasm
        }
     }
   

   
   INCFILE.H

     extern xdata unsigned char ioport;
   

   
   INCFILE.C

     xdata unsigned char ioport _at_ 0x8000
   

2. Create a project file and add the following files in the following order.
   • MAIN.C
   • MAIN.A51 (create when MAIN.C is compiled)
   • INCFILE.C
3. Turn off the "Include in Link/LIB" checkbox for MAIN.C. Turn ON the "Always Build" checkbox for both MAIN.C AND MAIN.A51
4. Build the project. There should be no errors.

Last Reviewed: Saturday, July 09, 2005