How to test millis() rollover on ESP32

Using Arduino Programming Questions
1

Hi.
I have a sketch that deals with time intervals and I and would like to test if I have coded everything correctly. So I'd like to test the behavior when the number of milliseconds rolls over (when it exceeds `4294967295 and restarts from 0, which happens after about 49 days since startup).
Is there a way to test without waiting 49 days ?
I have found that for Arduino boards the number of millis can be forced as follows:

extern unsigned long timer0_millis;
void setup() {
   ...
  noInterrupts();
  timer0_millis = 4294901760;
  interrupts();
  ...

However this code fails to compile on ESP32 with "undefined reference to `timer0_millis'"

How can I do on ESP32 ?
Dario

2

You could show the code, so we can check if millis() is used correctly.

3

You could use the ESP32's 64-bit timer capability. That will give you microsecond-resolution and you won't have to worry about rollover for more than 290,000 years.

4

You can use
unsigned long Mymillis = millis0;
in setup and periodically check that Mymillis is < millis() at the bottom of loop()

but, gfvalvo suggestion makes more sense.

5

If you use this calculation the roll-over of millis() is handled the right way automatically

define all variables that deal with millis() as unsigned long. Because the return-value of function millis() is of type unsigned long

unsigned long currentMillis;
unsigned long myInterval;
unsigned long startMillis;

if (currentMillis - startMillis >= myInterval) {
  // time for timed action
}

The integer-math of unsigned integers handles rollover automatically right.
you are doing the math in the if-conditions with variables of type unsigned long.

This means you can do the test with variables that you assign a value short before rollover

currentMillis = 200; // currentMillis short after rollover

startMillis = 4294967295 - 100; // snapshot of time short before rollover

serial.println(currentMillis - startMillis);

I did some research trying to find the library that defines the function millis() for ESP32 but had no success so far

best regards Stefan

6

Try this code.

RV mineirin

//-----------------------------------------------------
void setup() {
  Serial.begin(115200);
}
//-----------------------------------------------------
void loop() {
  int long abc = 0;
  abc = esp_timer_get_time();   // ESP32 Fuction similar to micros()
  Serial.println(abc);          // Some delay  add
  delay(1);                     // Delay 1000 uSeconds
}
7

In the file ...packages\arduino\hardware\mbed\1.1.6\cores\arduino\wiring.cpp

I found this

unsigned long millis()
{
  return t.read_ms();
}

best regards Stefan

8

Thank you for all your answers. At the end I decided to use the esp_timer_get_time() function and use micros. I also changed any variable used to store micros to the "long long" type.
Dario

9

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