How to Detect First Boot After Burning Program to Flash

I will write about Arduino, but this technique is relevant for any embedded situation.

Many applications require retaining data such settings or parameters between resets. On the Arduino, the already existing EEPROM of the Atmega chip is a common solution for this problem.

For the Arduino, the EEPROM library can be used to write or read values from the EEPROM.

It is important that the program does not read from the EEPROM on the first time it is run after it was burned. The reason is that the version that was burned, might have different representation of the data than the one stored in the EEPROM. This will cause "not so nice" problems that might not go away even after resetting.

To solve this, one need to know when a program is run the first time after it was burned, and use default values instead of reading from the EEPROM (and of course store these to the EEPROM for next time)

This is sometimes called IPL (Initial Program Load) which means the first time program is loaded into the RAM.

To detect IPL one can use a constant that changes every time a new version of your program is produced. This constant is compared with a value stored in the EEPROM, and if they are different, it means that a new program was burned and this is it's first boot after burning. After this, the value is stored in the EEPROM and subsequent boots will not be detected as IPL.

This constant can be managed manually, can be some preprocessor macro representing git commit hash or date and time macro.

For the Arduino example below, I used date and time macros which I find simple and robust:

/**
 * Address of the version data. This should never change between versions.
 */
#define EEPROM_ADDR_VERSION_DATE 0x0

/**
 * Your data should start after this location.
 * On gcc, __DATE_ is 11 chars long, __TIME__ is 8
 */
#define EEPROM_ADD_START_OF_DATA 0x13

/**
* Determine if this is the first power-up after
* fresh program was loaded into the flash.
*/
boolean is_initial_program_load()
{
    const String version_date = __DATE__ __TIME__;
    uint16_t len = version_date.length();
    boolean is_ipl = false;

    for (unsigned int i = 0; i < len; i++) {
        int addr = EEPROM_ADDR_VERSION_DATE + i;

        if (EEPROM.read(addr) != version_date[i]) {
            EEPROM.write(addr, version_date[i]);
            is_ipl = true;
        }
    }

    return is_ipl;
}