A problem in using sdcc interrupt

In sdcc, the interrupt handling function is identified by the keyword __interrupt, followed by the interrupt number. The list of 8051 interrupt numbers is as follows:

Interrupt # Description Vector Address
    0 External 0 0x0003
    1 Timer 0 0x000b
    2 External 1 0x0013
    3 Timer 1 0x001b
    4 Serial 0x0023
    5 Timer 2 (8052) 0x002b

Although it looks very simple, there is a small problem in the process of using it. Because I divided the program into two parts, main.c and timer.c, and the timer interrupt processing function timer0_isr in timer.c can never be executed. I checked the program and found no reason. By checking the source code in sdcc and searching the timer part code on the Internet, I did not find any problems with the initialization of timer0, which made me depressed. But I also found a difference between the two, that is, a declaration of the interrupt processing function was made before the main function, so I added this declaration in my program, and the program finally called the interrupt processing function, so I record it here. The complete program is as follows:

1. /* timer.c */  

2. #include   

3.   

4. #define OSC_FREQ 12000000UL  

5.   

6. #define TIMER_MODE0 0x00  

7. #define TIMER_MODE1 0x01  

8. #define TIMER_MODE2 0x02  

9. #define TIMER_MODE3 0x03  

10.   

11. volatile unsigned int count = 0;  

12.   

13. void timer0_isr(void) __interrupt 1  

14. {  

15.         count++;  

16.   

17.         TH0 = (65536-1000*(OSC_FREQ/12000000)) >> 8;  

18.         TL0 = (65536-1000*(OSC_FREQ/12000000)) & 0x00FF;  

19. }  

20.   

21. void timer0_init(void)  

22. {  

23.         TMOD &= 0xF0;  

24.         TMOD |= TIMER_MODE1; /* Timer 0 work on 16-bit timer mode */  

25.         TH0 = (65536-1000*(OSC_FREQ/12000000)) >> 8;  

26.         TL0 = (65536-1000*(OSC_FREQ/12000000)) & 0x00FF;  

27.         ET0 = 1; /* Enable timer 0 interrupt */  

28.         EA = 1;  

29.         TR0 = 1; /* Turn on timer 0 */  

30. }  

31.   

32. void delayms(unsigned int n)  

33. {  

34.         while (count <= n);  

35.   

36.         count = 0;  

37. }  

1. /* timer.h */  

2. #ifndef __TIMER_H  

3. #define __TIMER_H  

4.   

5. extern void timer0_init(void);  

6. extern void delayms(unsigned int n);  

7.   

8. #endif /* __TIMER_H */  

1. /* main.c */  

2. #include   

3.   

4. #include "timer.h"  

5.   

6. #define led1 P2_0  

7.   

8. void timer0_isr(void) __interrupt 1;  

9.   

10. void main(void)  

11. {  

12.         timer0_init();  

13.   

14.         while (1) {  

15.                 led1 = 0;  

16.                 delayms(1000);  

17.                 led1 = 1;  

18.                 delayms(1000);  

19.         }  

20. }  

Note: It has been verified that this problem does not occur in Keil.