原创 C51混和编程

 

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

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 uVision2, 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.

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