readwrite.pde

This is an example of how to use the M24L256 class. It writes a big block of data to the EEPROM, and then slowly reads it out again one little block at a time.

/*
 Copyright (C) 2011 James Coliz, Jr. <maniacbug@ymail.com>

 This program is free software; you can redistribute it and/or
 modify it under the terms of the GNU General Public License
 version 2 as published by the Free Software Foundation.
 */

#include <Wire.h>
#include <M24LC256.h>

// One EEPROM connected on address '0'
M24LC256 eeprom(0);

// Forward declaration of our sample data, just to move that stuff
// to the end of the file
extern unsigned char sample_data[];
extern unsigned int sample_data_len;

// Where on the eeprom we will write the sample data
const int eeprom_write_location = 0;

void setup(void)
{
  // Prepare everything
  Serial.begin(9600);
  Wire.begin();
  eeprom.begin();

  Serial.println("M24LC256/examples/readwrite/");

  // Write a really large chunk to a certain location on the EEPROM,
  // and see how long it takes
  unsigned long start_time = millis();
  eeprom.write(eeprom_write_location,sample_data,sample_data_len);
  unsigned long duration = millis() - start_time;

  Serial.print("Bytes written: ");
  Serial.println(sample_data_len);
  Serial.print("Time elapsed: ");
  Serial.println(duration);
  Serial.print("Bits per second: ");
  Serial.println(sample_data_len*8000L/duration);
}

// How many bytes to read every time through
const int read_length = 32;

// How long to wait after every reading
const int chunk_delay = 500;

// Current address to read from on the EEPROM
uint16_t current_read_location = eeprom_write_location;

// When to stop reading back from the EEPROM 
uint16_t end_read_location = eeprom_write_location + sample_data_len;

// Buffer to pull data down into
char buffer[read_length+1];

// Reads one chunk at a time real slowly and prints it to the Serial port
// Stops when it's read everything.
void loop(void)
{
  // If there are no chunks left to read, we are done.  Wait here.
  if (current_read_location >= end_read_location)
    while(1);

  // Read down a chunk from the eeprom
  uint16_t bytes_read = min(read_length,end_read_location-current_read_location);
  eeprom.read(current_read_location,buffer,bytes_read);

  // Insert a zero at the end, so we can print it as a string
  buffer[bytes_read] = 0;

  // Print out the buffer
  Serial.print(buffer);

  // Wait a bit
  delay(chunk_delay);

  // Recalculate where to read the next chunk 
  current_read_location += bytes_read;
}

// This data is generated from a file named "sample_data" by doing:
// xxd -i sample_data >> readwrite.pde

unsigned char sample_data[] = {
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};
unsigned int sample_data_len = 1133;

// vim:ci:sw=2 sts=2 ft=cpp