EEPROM eample

eeprom.c

/*
 * Example of how to use the avr-libc EEPROM functions;
 * http://www.nongnu.org/avr-libc/user-manual/group__avr__eeprom.html
 *
*/

#define F_CPU 32000000
#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/eeprom.h>
#include <util/delay.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "usart.h"
#include "clock.h"

#define STORED_STRING_LEN 13

uint8_t eeprom_stored_byte EEMEM = 0;
uint32_t eeprom_stored_long EEMEM = 0;
float eeprom_stored_float EEMEM = 0.0;
char eeprom_stored_string[STORED_STRING_LEN] EEMEM = "";

uint8_t stored_byte EEMEM = 0;
uint32_t stored_long EEMEM = 0;
float stored_float EEMEM = 0.0;
char stored_string[STORED_STRING_LEN] EEMEM = "";

int main(void) {
  sysclk_init();
  sei();

  // configure the usart1 (attached to USB) for 9600,8,N,1 to
  // show debugging info, see usart examples for explanation
  usart_init(1, 128, 128);
  usart_conf(1, 9600, 8, none, 1, 0, NULL);
  usart_map_stdio(1);
  usart_run(1);

  // wait for EEPROM to be ready
  eeprom_busy_wait();

  // read values from EEPROM
  stored_byte = eeprom_read_byte(&eeprom_stored_byte); // single byte
  stored_long = eeprom_read_dword(&eeprom_stored_long); // long integer
  stored_float = eeprom_read_float(&eeprom_stored_float); // floating point
  eeprom_read_block((void*)&stored_string, (void*)&eeprom_stored_string, STORED_STRING_LEN); // arbitrary block

  _delay_ms(1000);
  puts("Values read after power on;\r\n");

  printf("stored_byte = %u\r\n", stored_byte);
  printf("stored_long = %lu\r\n", stored_long);
  printf("stored_float = %f\r\n", stored_float);
  _delay_ms(100);
  printf("stored_string = %s\r\n", stored_string);

  stored_byte = 21;
  stored_long = 1234567890;
  stored_float = 27.72;
  strncpy(stored_string, "Hello World!", STORED_STRING_LEN);

  _delay_ms(100);
  puts("\r\nValues now set to;\r\n");

  printf("stored_byte = %u\r\n", stored_byte);
  printf("stored_long = %lu\r\n", stored_long);
  printf("stored_float = %f\r\n", stored_float);
  _delay_ms(100);
  printf("stored_string = %s\r\n", stored_string);

  // update values to EEPROM
  // the _update_ functions will test whether the existing EEPROM value is the same
  // before writing to save flash wear, there are also _write_ functions which do not
  eeprom_update_byte(&eeprom_stored_byte, stored_byte);
  eeprom_update_dword(&eeprom_stored_long, stored_long);
  eeprom_update_float(&eeprom_stored_float, stored_float);
  eeprom_update_block((void*)&stored_string, (void*)&eeprom_stored_string, STORED_STRING_LEN);

  _delay_ms(100);
  printf("\r\nValues written to EEPROM\r\n");
  printf("========================\r\n\r\n");
  _delay_ms(100); // let the characters go out the usart

  return 0;
}

Makefile

# Where is the toolchain unpacked?
TOOLBASE  ?= /usr/local/share/avr8-gnu-toolchain-linux_x86_64
# What MCU do we have on this board?
MCU       ?= atxmega64d4
# Port that Kakapo popped up on
PORT      ?= /dev/ttyUSB1
# Application name 
APP       = eeprom
# If using libkakapo, uncomment
LIBKAKAPO = -lkakapo
#Tools we'll need
CC        = $(TOOLBASE)/bin/avr-gcc
AVRDUDE   = /usr/bin/avrdude 
OBJCOPY   = $(TOOLBASE)/bin/avr-objcopy
CFLAGS    = -Os --std=c99 -funroll-loops -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums -Wstrict-prototypes -Wall -mcall-prologues -I. -I../../
# This is used specifically for printf in the EEPROM example
CFLAGS   += -Wl,-u,vfprintf -lprintf_flt -lm
CFLAGS   += -mmcu=$(MCU)
INCLUDE   = -L../../
OBJ       = $(patsubst %.c,%.o,$(wildcard *.c))

build: $(APP).hex

program: $(APP).hex
	$(AVRDUDE) -p $(MCU) -c avr109 -P $(PORT) -b 115200 -U flash:w:$(APP).hex -e

$(APP).hex: $(APP).elf
	$(OBJCOPY) -O ihex -j .text -j .data $< $@ 

$(APP).elf: $(OBJ)
	$(CC) $(CFLAGS) $(INCLUDE) $^ -o $@ $(LIBKAKAPO)

%.o: %.c %.h Makefile
	$(CC) -c $(CFLAGS) $< -o $@

clean:
	rm -f $(OBJ) $(APP).hex $(APP).elf