latest.c

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

#define USART_BAUDRATE 9600

//#define BAUD_PRESCALE ((((F_CPU / 16) + (USART_BAUDRATE / 2) / (USART_BAUDRATE))-1)
#define BAUD_PRESCALE 104

static volatile char rxbuff[100]; // to fill from USART
static volatile char parsebuff[120]; // separate buffer for parsing

static volatile unsigned int write_pointer = 0;

static unsigned int DEBUG_PIN = 5;
static unsigned int TIMEOUT = 3;
static unsigned int CRASH_LED = 4;

static volatile unsigned int need_data = 0;
static volatile unsigned int got_data = 0;
static volatile unsigned int timeout_counter = 0;
static volatile unsigned int error = 0;

ISR(USART_RXC_vect)
{
  if (need_data){
    if (write_pointer <= 99){
      rxbuff[write_pointer] = UDR0;
      if (rxbuff[write_pointer] == '\n'){
        got_data = 1;
        need_data = 0;
        write_pointer = 0;
      }
      write_pointer++;
    }
    else {
      write_pointer = 0;
      got_data = 1;
    }
  }
}


ISR(TIMER1_COMPA_vect)
{
   timeout_counter++;
   PORTB ^= (1 << CRASH_LED);
}


void tx_string(char* data)
{

  unsigned int i = 0;
  while((data[i] != '\n') && (i < 100))
  {
    while (!( UCSR0A & (1 << UDRE0))){}
    UDR0 = data[i];
    i++;
  }
}


void initialise_timer(void)
{
   TCCR1B |= (1 << WGM12); // Configure timer 1 for CTC mode
   TIMSK1 |= (1 << OCIE1A); // Enable CTC interrupt
   OCR1A   = 15624; // Set CTC compare value
   TCCR1B |= ((1 << CS10) | (1 << CS12));
}


void initialise_USART(void)
{
  UCSR0B = ((1 << RXEN0) | (1 << TXEN0)); // enable TX and RX lines

  UCSR0C = (1 << USBS0) | (3 << UCSZ00); // set 8 data bits, 2 stop bits

  // set higher and lower parts of 16 bit register for setting baud rate
  UBRR0H = (BAUD_PRESCALE >> 8);
  UBRR0L = BAUD_PRESCALE;

  UCSR0B |= (1 << RXCIE0); // enable RX_complete interrupt
}


void parse_data(void)
{
 tx_string(parsebuff);
}


int main(void)
{
  cli();
  DDRB |= (1 << DEBUG_PIN) | (1 << CRASH_LED);
  initialise_timer();
  initialise_USART();
  sei(); //  Enable global interrupts

  for (;;){
    need_data = 1; // I need data!
    while ((!got_data) && (timeout_counter < TIMEOUT)){} // do nothing (will be more efficient eventually)

    if (timeout_counter >= TIMEOUT){
      tx_string("timeout...\n"); // BEWARE: tx_string needs a \n, I think... needs confirmation
      PORTB ^= (1 << DEBUG_PIN);
      error = 1;
    } else if (error == 0) {
      need_data = 0; 
      strncpy(parsebuff, rxbuff, sizeof(rxbuff));
      parse_data();
      need_data = 1;
    } else {
      tx_string("Got error...\n"); 
    }
    timeout_counter = 0;
  }
}