[avr-gcc-list] basic UART Transmit interrupt problem

[Woodward, Mark P]

Hello all,

I run an atmega128L and am currently trying to transmit to the uart using
the transmit interrupt.  The problem is, when I send a byte after enabling
the transmit interrupt via

  UCSR0B = (1<<TXEN)|(1<<TXCIE);
  udr0 = 'A';

the byte gets sent, but then the program restarts from main, without
triggering my interrupt.  It's weird behavior.  Any help would be greatly
appreciated.  Here is the code.

#include <avr/interrupt.h>
#include <avr/io.h>
#include <avr/signal.h>

static volatile unsigned char *uart_data_ptr;
static volatile unsigned char uart_counter;
static volatile unsigned char led;

SIGNAL( SIG_UART_TRANS ) {
  uart_data_ptr++;

  if(--uart_counter)
    outp(*uart_data_ptr, UDR0);
}

void setRedLed(int on) {
  if(on) {
    cbi(PORTA, 2);
  } else {
    sbi(PORTA, 2);
  }
}

void initRedLed(void) {
  sbi(DDRA, 2);
  setRedLed(0);
}

//I am transmitting at 57600
void init(void) {
  UBRR0H = 0;
  UBRR0L = 15;

  UCSR0A = 1<<U2X;

  UCSR0B = (1<<TXEN)|(1<<TXCIE);

  UCSR0C = (1<<UCSZ1)|(1<<UCSZ0);
}

void uart_send(unsigned char *buf, unsigned char size) {
  if(!uart_counter) {
    uart_counter = size;
    uart_data_ptr = buf;
    UDR0 = *buf;
    // CRASHES HERE AND JUMPS BACK TO MAIN,
    // THE BYTE DOES GET SENT
    // DOESN'T CRASH IF I DON'T ENABLE TXCIE
  }
}

int main(void) {
  unsigned char i, j, k, l, m;

  initRedLed();

  // Debug to know restarted
  led = 0;
  for(m=0; m<10; m++) {
    setRedLed(!led);
    led = ~led;
    for(i=0; i<255; i++)
      for(j=0; j<255; j++)
        for(l=0; l<100; l++)
          k++;
  }

  init();
  sei();

  uart_send("HELLO WORLD", 12);

  for(;;) { k++; }
}