add eeprom library explicitly

digistump-avr/libraries/EEPROM/examples/eeprom_crc/eeprom_crc.ino

@@ -0,0 +1,50 @@
+/***
+    Written by Christopher Andrews.
+    CRC algorithm generated by pycrc, MIT licence ( https://github.com/tpircher/pycrc ).
+	
+	A CRC is a simple way of checking whether data has changed or become corrupted.
+	This example calculates a CRC value directly on the EEPROM values.
+	The purpose of this example is to highlight how the EEPROM object can be used just like an array.
+***/
+
+#include <Arduino.h>
+#include <EEPROM.h>
+
+void setup(){
+  
+  //Start serial
+  Serial.begin(9600);
+  while (!Serial) {
+    ; // wait for serial port to connect. Needed for Leonardo only
+  }
+
+  //Print length of data to run CRC on.
+  Serial.print( "EEPROM length: " );
+  Serial.println( EEPROM.length() );
+  
+  //Print the result of calling eeprom_crc()
+  Serial.print( "CRC32 of EEPROM data: 0x" );
+  Serial.println( eeprom_crc(), HEX );
+  Serial.print( "\n\nDone!" );
+}
+
+void loop(){ /* Empty loop */ }
+
+unsigned long eeprom_crc( void ){
+  
+  const unsigned long crc_table[16] = {
+      0x00000000, 0x1db71064, 0x3b6e20c8, 0x26d930ac,
+      0x76dc4190, 0x6b6b51f4, 0x4db26158, 0x5005713c,
+      0xedb88320, 0xf00f9344, 0xd6d6a3e8, 0xcb61b38c,
+      0x9b64c2b0, 0x86d3d2d4, 0xa00ae278, 0xbdbdf21c
+  };  
+  
+  unsigned long crc = ~0L;
+  
+  for( int index = 0 ; index < EEPROM.length()  ; ++index ){
+    crc = crc_table[( crc ^ EEPROM[index] ) & 0x0f] ^ (crc >> 4);
+    crc = crc_table[( crc ^ ( EEPROM[index] >> 4 )) & 0x0f] ^ (crc >> 4);    
+    crc = ~crc;
+  }
+  return crc;
+}