I got several warnings when I compile the following code using TIMER0 interrupt when it overflows. void main(void) { //----------------------------------------// interrupt TMOD = (TMOD & 0xF0) | 0x01; ET0 = 1; TR0 = 1; EA = 1; //Timer to overflow every 65536 clocks //and prinf "testing" while(1) { //do nothing } } ////-----------// void timer0_ISR(void) interrupt 1 { printf ("testing"); } //////////////////////// I got a warning message during linking: *** warning 15: MULTIPLE CALL TO SEGMENT SEGMENT: ?PR?PRINTF?PRINTF CALLER1: ?PR?TIMER0_ISR?MY_FILE CALLER2: ?C_C51STARUP