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Topic: Storing Strings in EEPROM from Serial Input Example (Read 2149 times) previous topic - next topic


Here is a short example demonstrating taking serial string input and storing and retrieving to and from EEPROM. This is done using EEMEM and <avr.eeprom.h>. I also demonstrate using PSTR-like functionality to keep serial response strings in flash but "print" them to serial directly, without copying them into a temp array using PROGMEM.

For brevity and laziness, I define three separate EEMEM strings and select them via a case statement. I am not sure though EEMEM will handle the pointer to pointer setup you'd need to fetch the start address of the char array inside another array. Anyone try it? Also, I have seen many examples using structs. I should try that too, but held off since I have to look into whether you have to copy the whole thing into RAM or can just copy a specific member of the struct.

Here's the code: (it wouldn't fit here)

I hope this is helpful. Comments are appreciated.


You've declared EEPROM_BYTES as 1024, but a 168 has only 512 bytes of EEPROM, and a MEGA2560 has 4096 bytes.
This would be better defined this value using one of the processor-specific predefines
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.
I speak for myself, not Arduino.


Thanks for the reply. I've never used predefines but here's an example:

CPU Type and How to Determine Arduino Bord

According to selected target processor, compiler defined constant by processor name.
Constant    CPU    Board
__AVR_ATmega168__    ATmega 168    Arduino Decimilia and older
__AVR_ATmega328P__    ATmega 328P    Arduino Duemilanove and Uno
__AVR_ATmega1280__    ATmega 1280    Arduino Mega
__AVR_ATmega2560__    ATmega 2560    Arduino Mega 2560

So by testing of these constants you can determine board type. For example:

#if not (defined(__AVR_ATmega2560__) || defined(__AVR_ATmega1280__))
    #error Sorry dude, this program works only on Arduino Mega

Coding Badly


#define EEPROM_BYTES 1024


#define EEPROM_BYTES (E2END+1)

Problem solved.


Further thoughts on storing data in EEPROM as a struct...

The example given here: http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&t=38417&start=220&postdays=0&postorder=asc&highlight=

is pretty good in that it uses <avr/eeprom.h> and does not require you to reference a memory address when storing/retrieving data. The downside is that you have to copy the whole struct from EEPROM into RAM, which isn't so good for storing and retrieving strings. There must be a way to dereference one value at a time from EEPROM into RAM though.

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