BL51: UNRESOLVED SYMBOL ?C_STARTUP

Information in this article applies to:

• C51 All Versions

SYMPTOMS

When writing single-file projects using in-line assembly, the linker produces the following warning:

*** WARNING L1: UNRESOLVED EXTERNAL SYMBOL
     SYMBOL:    ?C_STARTUP
     MODULE:    main.obj    (MAIN)

For example, the following program:

#include <reg52.h>

void main()  {
  unsigned char i;
  unsigned char cur[20];

  for( i = 0; i < 20; i++)  {
    #pragma asm
      mov   A, x;
      movc  A, @A+PC;
    #pragma endasm
  }
}

When compiled, assembled, and linker in µVision2, generates the warning above. To translate this file, you must enable the following 2 checkboxes in Project - Options for file - Properties:

• Generate Assembler SRC File
• Assembler SRC File

CAUSE

When you compile all your C modules with the SRC directive and the assembler, the linker does not detect the required C run-time libraries (because the files were assembled). In this case, you must add the libraries to your project manually.

RESOLUTION

For a project in the SMALL memory model that uses no floating point arithmetic, C51S.LIB is required.

For a project in the LARGE memory model that uses floating-point, C51FPL.LIB and C51L.LIB are required.

If a project uses floating arithmetic, it is important that C51FPx.LIB is included before the standard library file C51x.LIB. Otherwise printf and scanf will not work with floating-point numbers.

When you are using µVision, you may simply add the require library file(s) to the project in the same way as you are adding source files.

SEE ALSO

• BL51: UNRESOLVED EXTERNAL SYMBOL FOR MATH AND FP ROUTINES
• BL51: NOT FINDING SOME FUNCTIONS IN LIBRARIES
• BL51: WARNING L1 (UNRESOLVED EXTERNAL) USING INLINE ASSEMBLY
• C51: CALLING ASSEMBLY ROUTINES FROM C
• µVision: GREY CHECK BOXES IN FILE AND GROUP OPTIONS

FORUM THREADS

The following Discussion Forum threads may provide information related to this topic.

• Error: UNRESOLVED EXTERNAL SYMBOL and REFERENCE MADE TO UNRESOLVED EXTERNAL
• UNRESOLVED EXTERNAL SYMBOL
• working with right shift operators in C
• help on keil
• cannot link...says "?C_START" unresolved
• Error L127 and L128
• PROBLEM WHILE INSERTING ASM CODE INTO C FILES
• inline assembly help linker error
• keil

Last Reviewed: Thursday, December 22, 2005