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By highno
#80288 Library RTCVars for ESP8266 Arduino released



This library eases the storage of variables in reset-safe RTC memory. Variables stored there survive all kinds of resets as long as there is no hard reset. It provides boilerplate code to securely store relevant state data in RTC memory so it may survive (unexpected) reboots or deep sleeps. Supports ESP only at this time, will change in the future.

Aim of the library is to make an integration into existing projects as easy as possible.

Basic example

Code: Select all#include <RTCVars.h>
RTCVars state; // create the state object

int reset_counter;                      // we want to keep these values after reset
int program_step;

void setup() {
  Serial.begin(115200);                 // allow debug output
  state.registerVar( &reset_counter );  // we send a pointer to each of our variables
  state.registerVar( &program_step );

  if (state.loadFromRTC()) {            // we load the values from rtc memory back into the registered variables
    Serial.println("This is reset no. " + (String)reset_counter);
    state.saveToRTC();                  // since we changed a state relevant variable, we store the new values
  } else {
    reset_counter = 0;                  // cold boot part
    Serial.println("This seems to be a cold boot. We don't have a valid state on RTC memory");
    program_step = 0;

void loop() {
  // do your work here - try to reset your chip externally or internally but don't power off...
  Serial.println("Current state is " + (String)program_step);
  program_step = (program_step == 7) ? 1 : program_step + 1;
  Serial.println("New state is " + (String)program_step);
  state.saveToRTC();                    // there are no parameters because it only needs the vars' definiton once

First the library is included by #include <RTCVars.h>. Then an RTCVars object named state is created via RTCVars state;. This object now is the interface to all functionality. Be sure to register all variables before reading the old state from RTC memory. The state is invalid if the registered variables differ in total size to the saved state. It is good practice to use globally defined vars only and register all of them in the setup() function. If you really need to keep track of different, state-specific variables, look at the advanced usage (on GitHub).

Registering does nothing but keeping track of where the variables are to find in memory. Of course reading the state from RTC memory would require to save the values in the corresponding variables. Therefore you need to register them even before you call state.loadFromRTC(). If everything works out, the call returns true. If not there are problems with the state or it has been a cold boot. See advanced usage for further information on error handling.

Later on, everytime a change is made to some of the vars registered and have a consistent state is established, state.saveToRTC() is called to push these values to RTC memory.

Supported types and size

Please note, that there are two limits in this lib: memory and the number of managed variables. Due to the fact how storage of vars is organized, there is a fixed upper boundry other than memory. By default, the limit is 32 variables, the types are byte, char, int, long, float. Since these types do not exceed 8 bytes each, the RTC memory is not the limit here (512 bytes - 28 starting offset - 7 header/checksum = 477 bytes). See advanced usage (on GitHub) for more functionality to control these settings.
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#83007 Hi,

Thanks for an easy to use library! I've successfully used this for storing ints and floats, but I've not been able to store char array. I can define a char var[32], and then saveToRTC, but then after a loadFromRTC, I only get the first character... Here's a rough example...

char text[32];
state.registerVar( &text[32] );
// set the text somewhere, eg to "example"
// after coming back from deep sleep
println(sizeOf(text)); // returns 32
println(text); // returns only "e"


thanks in advance,