Mixed programming of A51 and C language

I spent a whole morning studying and wrote a program. It is small but complete. I hope that people who are learning this can spend less time searching for information and master it faster.

#include 
/****Define in assembly*****/
extern void delay(void) ;
extern add(int a,int b);
//Test assembly call code (do not want to use assembly directly to run the main program)
extern void test();
/***Code segment defined in assembly****/
extern unsigned char cc;

// Function defined in C language
void delay_c();
unsigned int addcc(unsigned int wd1,unsigned int wd2);
//Data segment defined in C language
unsigned int aa;
unsigned int bb;

void main()
{
  
   delay();
   cc=add(10,15);
   test();
   while(1);
}
void delay_c()
{
  unsigned char cc;
  cc=0xff;
  while(cc--);
}
unsigned int addcc(unsigned int wd1,unsigned int wd2)
{
unsigned int cl;
cl=wd1+wd2;
return cl;
}


delay.asm


NAME ONE ; name of the module
;ORG 1000H ;Starting unit where the function is stored
?PR?delay?ONE SEGMENT CODE ; mark the definition location of the function
?PR?_add?ONE SEGMENT CODE
?PR?test?ONE SEGMENT CODE
cc DATA 33H ;Directly define the data address
PUBLIC delay ; declared as global
PUBLIC _add
PUBLIC test
PUBLIC cc ; declare global
EXTRN DATA(aa); Note that this is extrn instead of extern in C. Defined in C
EXTRN DATA(bb)
EXTRN CODE(delay_c)
EXTRN CODE(_addcc); I did not test the online information with parameters EXTRN CODE(addcc) successfully.

Logically, the name should be added with _fun, which is a definition method with parameters.
;EXTRN DATA(?_addcc?BYTE) ;I have not been able to successfully pass this method to upload parameters online, so I directly processed the data on the register.

   RSEG ?PR?delay?ONE ; (without parameter function) relocate the code position of the function
delay:
   MOV R0 , #44H
   DJNZ R0,$
   RET
  RSEG ?PR?_add?ONE ; (function with parameters) The parameters are automatically prevented from being put into the register. You can check it online.

Here 15 is stored in R7, R6 and 10 is stored in R5, R4
_add:
   MOV A,R5
   ADD A,R7
   MOV R7,A
   MOV A,R4
   ADDC A,R6
   MOV aa,R7
   RET

RSEG PR test ONE
test:
  ; Use C function without parameters
  CALL delay_c
  ;Call a C function with parameters
  MOV R5,#15
  MOV R7,#11
  LCALL _addcc
  MOV cc,R7
  RET
  END ; End of program