Hi All,

Im trying to send data over the serial port. But instead of sending it every cycle of the while loop i want to send data every approx seven seconds so i have added an interrupt and an in statement but it hasnt worked.

Is there something wrong with my code is it a more fundamental issue to do with printf_P?

#define F_CPU 14745600

#include <stdio.h>
#include <math.h>

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/pgmspace.h>
#include <inttypes.h>

#include "../libnerdkits/delay.h"
#include "../libnerdkits/lcd.h"
#include "../libnerdkits/uart.h"

double on;
double time = 0;

int main() {

 TIMSK1 |= (1 << TOIE1); // Enable overflow interrupt 
 sei(); // Enable global interrupts

 TCCR1B |= (1 << CS11);

uart_init();
FILE uart_stream = FDEV_SETUP_STREAM(uart_putchar, uart_getchar,....        
_FDEV_SETUP_RW);

stdin = stdout = &uart_stream;

while(1) {

  if( on == 1 )
  {

  printf_P(PSTR("hello\r\n"));
  time = 0;
  on = 0;
  }

  }

  return 0;
 }

 ISR(TIMER1_OVF_vect) 
 {

  time++;

  if (time == 200)
  {
  on = 1;
  }
  }

"on" needs to be "volatile char" instead of "double". I'd also make "time" a char instead of a double so it only takes one byte instead of four.

Hi bretm,

Thanks fro your reply. I tried what you said and it didnt work i then changed 'time' from a char to an int and it now works. on a side note.. what the reason you need to make on a volatile char? would a volatile int/ uint_8 work?

thanks kemil

char is a byte, the same as uint8_t. If it only works with int, which is 16 bits, you must be using a value greater than 255 somewhere, which I couldn't tell from the code posted above.