Yes, no waits inside the serial interrupt.
The problem with setting a flag is the possible delay before the main routine handles it. There may be an alternative.
Call send_char from inside the serial interrupt.While in send_char do a reti. Then the interrupts are free, and you stay in send_char. There is no delay inside the serial interrupt, and you handle the sending immediately.
void send_char (char ch){
freeint(void);
... now handle the waiting and sending here
}//here you go back to where you were when the serial interrupt occurred.
void freeint (void){
#pragma asm
reti
#endpragma asm
}
Regards
Johan Smit
}