//JTS2doLater: eeprom.c isn't wrapped into MVP yet 

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

/* These EEPROM bits have different names on different devices. */
#ifndef EEPE
		#define EEPE  EEWE  //!< EEPROM program/write enable.
		#define EEMPE EEMWE //!< EEPROM master program/write enable.
#endif

/* These two are unfortunately not defined in the device include files. */
#define EEPM1 5 //!< EEPROM Programming Mode Bit 1.
#define EEPM0 4 //!< EEPROM Programming Mode Bit 0.

/* Define to reduce code size. */
#define EEPROM_IGNORE_SELFPROG //!< Remove SPM flag polling.

//////////////////////////////////////////////////////////////////////////////

//Read one byte from a given EEPROM address.
//The CPU is halted for 4 clock cycles during EEPROM read.
//'addr' is EEPROM address to read.
//returns thebyte read from the EEPROM address.
unsigned char eeprom_get_char( unsigned int addr )
{
	do {} while( EECR & (1<<EEPE) ); // Wait for completion of previous write.
	EEAR = addr; // Set EEPROM address register.
	EECR = (1<<EERE); // Start EEPROM read operation.
	return EEDR; // Return the byte read from EEPROM.
}

//////////////////////////////////////////////////////////////////////////////

//Write one byte to given EEPROM address
//The CPU is halted for 2 clock cycles during EEPROM programming.

//The differences between the existing byte and the new value is used
//to select the most efficient EEPROM programming mode.

//When this function returns, the new EEPROM value is not available
//until the EEPROM programming time has passed. The EEPE bit in EECR
//should be polled to check whether the programming is finished.
//EEPROM_GetChar() function checks the EEPE bit automatically.

//'addr' is  EEPROM address to write.
//'new_value' is data to write.
void eeprom_put_char( unsigned int addr, unsigned char new_value )
{
	char old_value; // Old EEPROM value.
	char diff_mask; // Difference mask, i.e. old value XOR new value.

	cli(); // Ensure atomic operation for the write operation.
	
	do {} while( EECR & (1<<EEPE) ); // Wait for completion of previous write.
	#ifndef EEPROM_IGNORE_SELFPROG
	do {} while( SPMCSR & (1<<SELFPRGEN) ); // Wait for completion of SPM.
	#endif
	
	EEAR = addr; // Set EEPROM address register.
	EECR = (1<<EERE); // Start EEPROM read operation.
	old_value = EEDR; // Get old EEPROM value.
	diff_mask = old_value ^ new_value; // Get bit differences.
	
	// Check if any bits are changed to '1' in the new value.
	if( diff_mask & new_value ) {
		// Now we know that _some_ bits need to be erased to '1'.
		
		// Check if any bits in the new value are '0'.
		if( new_value != 0xff ) {
			// Now we know that some bits need to be programmed to '0' also.
			
			EEDR = new_value; // Set EEPROM data register.
			EECR = (1<<EEMPE) | // Set Master Write Enable bit...
			       (0<<EEPM1) | (0<<EEPM0); // ...and Erase+Write mode.
			EECR |= (1<<EEPE);  // Start Erase+Write operation.
		} else {
			// Now we know that all bits should be erased.

			EECR = (1<<EEMPE) | // Set Master Write Enable bit...
			       (1<<EEPM0);  // ...and Erase-only mode.
			EECR |= (1<<EEPE);  // Start Erase-only operation.
		}
	} else {
		// Now we know that _no_ bits need to be erased to '1'.
		
		// Check if any bits are changed from '1' in the old value.
		if( diff_mask ) {
			// Now we know that _some_ bits need to the programmed to '0'.
			
			EEDR = new_value;   // Set EEPROM data register.
			EECR = (1<<EEMPE) | // Set Master Write Enable bit...
			       (1<<EEPM1);  // ...and Write-only mode.
			EECR |= (1<<EEPE);  // Start Write-only operation.
		}
	}
	
	sei(); // Restore interrupt flag state.
}

//////////////////////////////////////////////////////////////////////////////

void memcpy_to_eeprom_with_checksum(unsigned int destination, char *source, unsigned int size) {
  unsigned char checksum = 0;
  for(; size > 0; size--) { 
    checksum = (checksum << 1) || (checksum >> 7);
    checksum += *source;
    eeprom_put_char(destination++, *(source++)); 
  }
  eeprom_put_char(destination, checksum);
}

//////////////////////////////////////////////////////////////////////////////

int memcpy_from_eeprom_with_checksum(char *destination, unsigned int source, unsigned int size) {
  unsigned char data, checksum = 0;
  for(; size > 0; size--) { 
    data = eeprom_get_char(source++);
    checksum = (checksum << 1) || (checksum >> 7);
    checksum += data;    
    *(destination++) = data; 
  }
  return(checksum == eeprom_get_char(source));
}