AVR Freaks

Here is the properly posted code.

Thanks for the advice, Clawson

#include <avr/io.h>     	// Device specifics.
#include <avr/interrupt.h>     // Interrupt specifics.
#include <util/delay_basic.h>

//Desired baudrate...choose one, comment the others.
#define BR_9600     
//#define BR_19200    
//#define BR_38400      

//This section chooses the correct timer values for the chosen baudrate.


#ifdef  BR_9600					//****CHECK BIT VALUES**** These are for 16MHz, prescalar = 32
    #define TICKS2COUNT         52  //Ticks between two bits.
    #define TICKS2WAITONE       52  //Wait one bit period.
    #define TICKS2WAITONE_HALF  78  //Wait one and a half bit period.
	
#endif  
#ifdef  BR_19200				//****CHECK BIT VALUES**** These are for 16MHz, prescalar = 8
    #define TICKS2COUNT          104  //Ticks between two bits.
    #define TICKS2WAITONE        104 //Wait one bit period.
    #define TICKS2WAITONE_HALF   156 //Wait one and a half bit period.
#endif
#ifdef  BR_38400				//****CHECK BIT VALUES**** These are for 16MHz, prescalar = 8
    #define TICKS2COUNT          52  //Ticks between two bits.
    #define TICKS2WAITONE        52  //Wait one bit period.
    #define TICKS2WAITONE_HALF   78  //Wait one and a half bit period.
#endif

#define INTERRUPT_EXEC_CYCL   9   // Cycles to execute ISR after interrupt.

//Some IO, timer and interrupt specific defines.

//MCU definitions - CHECK for proper Timer SFR definitions
#if  (defined(__ATmega8__)) 
  #define ENABLE_TIMER_INTERRUPT( )       ( TIMSK |=_BV(OCIE2))
  #define DISABLE_TIMER_INTERRUPT( )      ( TIMSK &= ~_BV(OCIE2))
  #define CLEAR_TIMER_INTERRUPT( )        ( TIFR |=_BV(OCF2))
  #define ENABLE_EXTERNAL0_INTERRUPT( )   ( GICR |=_BV(INT0))
  #define DISABLE_EXTERNAL0_INTERRUPT( )  ( GICR &= ~_BV(INT0))
  #define TX_PIN           PD6          //Transmit data pin
  #define RX_PIN           PD2          //Receive data pin, must be INT0
  #define TCCR             TCCR2        //Timer/Counter Control Register
  #define TCCR_P           TCCR2     	//Timer/Counter Prescaler
  #define OCR              OCR2       //Output Compare Register
  #define TCNT			   TCNT2		//Tmr counter register
  #define EXT_IFR          GIFR         //Ext Interrupt Flag Register
  #define EXT_ICR          MCUCR        //Ext Interrupt Control Register
//#define TIMER_COMP_VECT  TIMER0_COMP_vect  //!< Timer Compare Interrupt Vector

#elif (defined (__AVR_ATmega328P__))
  #define ENABLE_TIMER_INTERRUPT( )       ( TIMSK2 |= ( 1<< OCIE2A ) )
  #define DISABLE_TIMER_INTERRUPT( )      ( TIMSK2 &= ~( 1<< OCIE2A ) )
  #define CLEAR_TIMER_INTERRUPT( )        ( TIFR2 |= ((1 << OCF2A) ) )
  #define ENABLE_EXTERNAL0_INTERRUPT( )   ( EIMSK |= ( 1<< INT0 ) )
  #define DISABLE_EXTERNAL0_INTERRUPT( )  ( EIMSK &= ~( 1<< INT0 ) )
  #define TX_PIN           PORTD6    //Transmit data pin,PDx is for ATMega8
  #define RX_PIN           PORTD2          // Receive data pin, must be INT0
  #define TCCR             TCCR2A        // Timer/Counter Control Register
  #define TCCR_P           TCCR2B   	 //Timer/Counter ControlPrescaler 
  #define OCR              OCR2A         // Output Compare Register
  #define TCNT			   TCNT2		//Tmr counter register
  #define EXT_IFR          EIFR          // External Interrupt Flag Register
  #define EXT_ICR          EICRA         // External Interrupt Control Register
  #define TIMER_COMP_VECT  TIMER2_COMPA_vect  // Timer Compare Interrupt Vector

#endif

#define TRXDDR  DDRD			//Set Tx/Rx ports, pins
#define TRXPORT PORTD
#define TRXPIN  PIND

#define SET_TX_PIN( )    ( TRXPORT |=_BV(TX_PIN))
#define CLEAR_TX_PIN( )  ( TRXPORT &= ~_BV(TX_PIN))
#define GET_RX_PIN( )    ( TRXPIN & (_BV(RX_PIN)))


//Type defined enumeration holding software UART's state.
 
typedef enum
{
    IDLE,             //Idle state, both transmit and receive possible.
    TRANSMIT,                          // Transmitting byte.
    TRANSMIT_STOP_BIT,                 //Transmitting stop bit.
    RECEIVE,                           //Receiving byte.
    DATA_PENDING                 //Byte received and ready to read.

}AsynchronousStates_t;

static volatile AsynchronousStates_t state;    //Holds state of UART.
static volatile unsigned char SwUartTXData;     //Data to be Tx'ed.
static volatile unsigned char SwUartTXBitCount; //TX bit counter.
static volatile unsigned char SwUartRXData;     //Storage for Rx'ed bits.
static volatile unsigned char SwUartRXBitCount; //RX bit counter.


// External interrupt service routine.

ISR(INT0_vect)	//Receive interrupt - falling edge
{

  state = RECEIVE;                  // Change state
  DISABLE_EXTERNAL0_INTERRUPT( );   // Disable intr during the data bits.

  DISABLE_TIMER_INTERRUPT( );       // Disable timer to change its reg.
  TCCR_P &= ~(( 1 << CS21 )|( 1 << CS20 )); // Reset prescaler counter.

  TCNT = INTERRUPT_EXEC_CYCL;      // Clear counter register. Include time to run ISR.

  TCCR_P |= (( 1 << CS21 )|( 1 << CS20 ));  // Start prescaler clock.

  OCR = TICKS2WAITONE_HALF;         // Count 1.5 bits to sample first bit.

  SwUartRXBitCount = 0;             // Clear received bit counter.
  CLEAR_TIMER_INTERRUPT( );         // Clear interrupt bits
  ENABLE_TIMER_INTERRUPT( );        // Enable timer0 interrupt on again

}


// Timer2 interrupt service routine.

ISR(TIMER_COMP_VECT)
{

  switch (state) 
{
  // Transmit Byte.
  case TRANSMIT:
    // Output the TX buffer.
    if( SwUartTXBitCount < 8 ) 
	{            
      if( SwUartTXData & 0x01 )         // If LSB of the TX buffer is 1:
       { 
		SET_TX_PIN();                  // Send a logic 1 on the TX_PIN.
       }
      else 
	 {                                // Otherwise:
        	CLEAR_TX_PIN();                // Send a logic 0 on the TX_PIN.
       }
      SwUartTXData = SwUartTXData >> 1;     // Bitshift the TX buffer and
      SwUartTXBitCount++;                   // increment TX bit counter.
 	}

    //Send stop bit.
    else 
	{
      SET_TX_PIN();                         // Output a logic 1.
      state = TRANSMIT_STOP_BIT;
    	}
  break;

  // Go to idle after stop bit was sent.
  case TRANSMIT_STOP_BIT:
    DISABLE_TIMER_INTERRUPT( );           // Stop the timer interrupts.
    state = IDLE;                         // Go back to idle.
    ENABLE_EXTERNAL0_INTERRUPT( );        // Enable reception again.
  break;

  //Receive Byte.
  case RECEIVE:
    
//Count one period after the falling edge is trigged.
OCR = TICKS2WAITONE; 
    
    if( SwUartRXBitCount < 8 ) //Receiving, LSB first.
	{
        SwUartRXBitCount++;
        SwUartRXData = (SwUartRXData>>1);   // Shift due to receiving LSB first.
        if( GET_RX_PIN( ) != 0 ) 
		{
            SwUartRXData |= 0x80;     // If a logical 1 is read, let the data mirror this.
        	}
    	}

    //Done receiving
    else 
	{
	// Enter DATA_PENDING when one byte is rx'ed.        
state = DATA_PENDING; 
	// Disable this interrupt.
 		DISABLE_TIMER_INTERRUPT( );         
      // Reset flag not to enter the ISR one extra time.
		EXT_IFR |= (1 << INTF0 );   
       // Enable interrupt to receive more bytes. 
		ENABLE_EXTERNAL0_INTERRUPT( );  
    	}
  break;

  // Unknown state.
  default:        
    state = IDLE;          // Error, should not occur. Going to a safe state.
  } //end switch
}	// end intr


// Function to initialize the software UART.
//This function will set up Tx & Rx pins, tmr CTC mode, prescalar & interrupts. 
//Leaves init routine after setting uart in Rx mode by enabling ext INT0.

void initSoftwareUart( void )
{
  //Set PORT
  TRXPORT |=_BV(RX_PIN);       // RX_PIN is input, pulled up.
  TRXDDR |=_BV(TX_PIN);        // TX_PIN is output.
  SET_TX_PIN( );                    // Set the TX line to idle state.

  //Set Timer2
  DISABLE_TIMER_INTERRUPT( );	//(TIMSK &= ~_BV(OCIE2)) 
  TCCR = 0x00;    				//Ensure TCCR is initialised on power on
  TCCR_P = 0x00;    				
  TCCR |= (1 << WGM21);			// Timer in CTC mode.
  
  TCCR_P |= (( 1 << CS21 )|( 1 << CS20 )); // set prescaler.

  //Set External interrupt
  EXT_ICR = 0x00;                   // Init MCUCR
  EXT_ICR |= (1 << ISC01 );       // Interrupt on falling edge.
  ENABLE_EXTERNAL0_INTERRUPT( );    // Turn external interrupt on.

  //Internal State Variable
  state = IDLE;
}


// Send an unsigned char.
  
static void putChar( const unsigned char c )
{
  while( state != IDLE )
  {
    ;                // Don't send while busy receiving or transmitting.
  }

  state = TRANSMIT;
  DISABLE_EXTERNAL0_INTERRUPT( );  // Disable reception.
  SwUartTXData = c;             // Put byte into TX buffer.
  SwUartTXBitCount = 0;         //set bit count 0

  TCCR_P &= ~(( 1 << CS21 )|( 1 << CS20 )); // Reset prescaler counter.
  TCNT = 0;                        // Clear counter register.
  TCCR_P |= (( 1 << CS21 )|( 1 << CS20 )); // CTC mode. Start prescaler clock.

  CLEAR_TX_PIN();               // Clear TX line...start of preamble.

  CLEAR_TX_PIN( );                 // Clear TX line...start of preamble

  ENABLE_TIMER_INTERRUPT( );        // Enable o/p compare interrupt
}


// Print unsigned char string.
//param  const unsigned char* Pointer to the string that is to be printed.
//retval void
 
void print_string( const unsigned char *data )
{
  OCR = TICKS2WAITONE;				//set bit times
  while( *data != '\0' )
  {
    putChar( *data++ );
  }
}



main.c


#include <avr/io.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <avr/interrupt.h>
#include <util/delay.h>

#include "ds18b20.h"

//function declarations
void initSoftwareUart( void );
void print_string( const char * );

int main(void) 
{

	//init uart
	initSoftwareUart();

	//init interrupt
	sei();
	
	print_string("DS18B20 Temperature Probe\r\n");
	
	for (;;) 
	{
		//software serial routines
		print_string("Temperature: "); 

		print_string("\r\n");
	
		_delay_ms(1000);
		
	}
	
	return 0;
}

Sparrow2, I am using a standard Arduino Mini Pro, ATMega 328P, 16MHz. But I am using it as a bare board, not with Arduino IDE. 

I will check your good advice to have the delay loop in between cli() and sei(). This will surely disable the interrupts during the delay execution, and enable after.

As mentioned in another reply, I will check out with the simulator, it should be a bit easy.

DocJC, the receiving data pin is INT0, enabled to generate interrupt on falling edge. But I am not using the system in receive mode at this juncture, so am I right in saying this may not matter? Or is there some "hidden" hardware / software issue here? The receive part begins only with an INT0 falling edge, which is not the case here.

"The difference between your initial power up data string transmission and your subsequent data string transmissions is that you have just finished your USART initialization subroutine the first time.

Presumably, but perhaps erroneously, one of the setup parameters was somehow trashed on the final exit of the Tx  Data ISR and the PutChar routine."

Yes, this will come out when I run through the simulator. Now that the delay is reduced, the simulation may not take too long. Also I only have to check the first time after the delay loop to know whether the string is corrupted.

"In theory it shouldn't make a difference, but what happens if you disable interrupts, rerun your InitSoftwareUart routine, and then re-enable interrupts, AFTER your Main Loop's delay, before the code loops back to the PrintString instruction."

Doing the above may not help if the string is corrupted. It will still stay corrupted.

Yes Clawson. The string "Temperature: " (without quotes) is located at 011B to 0128 in RAM. Using breakpoints at proper locations in the code and running the program, I could not see any corruption in this string. 

It seems there is some timing problem as others have mentioned, which is consistent, since the subsequent lines all have same bytes in the strings. 

I removed the software delay (_delay_ms()) an used the Timer1 in CTC mode for delays. Here too the same issue occurs. This means there is some timing changes that happens after a delay. 

I will have to check the codes in depth and see what I can do. This issue has to be resolved so that we can use software uart when we are short of the AVR's UART.

If the start point in the timing cycle is wrong, then the bytes should relate, either by left shift or right shift. E.g., the first byte which is supposed to be 0x54 ('T'), should be either 0xA8 (if <<)  or 0x4A (if>>).

This is because the wrong bytes are consistently wrong, not random for each line. Hence timing shifts should be consistent. This is my logic, which may be corrected.