Using the SRC Directive

The Cx51 Compiler can create assembly source files that you assemble with the A51 Assembler. These SRC files can help you determine the argument passing conventions between C and assembly.

To create an assembly source file, you must use the SRC directive with the Cx51 Compiler. For example:

#pragma SRC
#pragma SMALL

unsigned int asmfunc1 (
  unsigned int arg)
{
return (1 + arg);
}

For this example, the compiler generates the following SRC file.

; ASM1.SRC generated from: ASM1.C

NAME    ASM1

?PR?_asmfunc1?ASM1   SEGMENT CODE
PUBLIC  _asmfunc1
; #pragma SRC
; #pragma SMALL
;
; unsigned int asmfunc1 (

                RSEG   ?PR?_asmfunc1?ASM1
                USING  0
_asmfunc1:
;---- Variable 'arg?00' assigned to Register 'R6/R7' ----
                      ; SOURCE LINE # 4
                      ; SOURCE LINE # 6
; return (1 + arg);
                      ; SOURCE LINE # 7
                MOV   A,R7
                ADD   A,#01H
                MOV   R7,A
                CLR   A
                ADDC  A,R6
                MOV   R6,A
; }
                      ; SOURCE LINE # 8
?C0001:
                RET
; END OF _asmfunc1

                END

In this example, note that the function name, asmfunc1, is prefixed with an underscore character signifying that arguments are passed in registers. The arg parameter is passed using R6 and R7.

The following example shows the assembly source generated for the same function with register parameter passing disabled by the NOREGPARMS directive.

; ASM2.SRC generated from: ASM2.C

NAME    ASM2

?PR?asmfunc1?ASM2    SEGMENT CODE
?DT?asmfunc1?ASM2    SEGMENT DATA
PUBLIC  ?asmfunc1?BYTE
PUBLIC  asmfunc1

                RSEG  ?DT?asmfunc1?ASM2
?asmfunc1?BYTE:
arg?00:          DS  2
; #pragma SRC
; #pragma SMALL
; #pragma NOREGPARMS
;
; unsigned int asmfunc1 (

                RSEG   ?PR?asmfunc1?ASM2
                USING  0
asmfunc1:
                      ; SOURCE LINE # 5
                      ; SOURCE LINE # 7
; return (1 + arg);
                      ; SOURCE LINE # 8
                MOV   A,arg?00+01H
                ADD   A,#01H
                MOV   R7,A
                CLR   A
                ADDC  A,arg?00
                MOV   R6,A
; }
                      ; SOURCE LINE # 9
?C0001:
                RET
; END OF asmfunc1

                END

Note in this example that the function name, asmfunc1, is not prefixed with an underscore character and that the arg parameter is passed in the ?asmfunc1?BYTE segment.