ESP32_S2_TimerInterrupt Library

ESP32_S2_TimerInterrupt library
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Why do we need this ESP32_S2_TimerInterrupt library

Features

This library enables you to use Interrupt from Hardware Timers on an ESP32-S2-based board.

The ESP32-S2 timer Interrupt control is different from that of ESP32, at least with the ESP32-S2 core v1.0.6. While the examples of current ESP32TimerInterrupt library can be compiled OK, they can’t run yet. That’s why this new ESP32_S2_TimerInterrupt library has been created.


As Hardware Timers are rare, and very precious assets of any board, this library now enables you to use up to 16 ISR-based Timers, while consuming only 1 Hardware Timer. Timers’ interval is very long (ulong millisecs).

Now with these new 16 ISR-based timers, the maximum interval is practically unlimited (limited only by unsigned long miliseconds) while the accuracy is nearly perfect compared to software timers.

The most important feature is they’re ISR-based timers. Therefore, their executions are not blocked by bad-behaving functions / tasks. This important feature is absolutely necessary for mission-critical tasks.

The ISR_Timer_Complex example will demonstrate the nearly perfect accuracy compared to software timers by printing the actual elapsed millisecs of each type of timers.

Being ISR-based timers, their executions are not blocked by bad-behaving functions / tasks, such as connecting to WiFi, Internet and Blynk services. You can also have many (up to 16) timers to use.

This non-being-blocked important feature is absolutely necessary for mission-critical tasks.

You’ll see blynkTimer Software is blocked while system is connecting to WiFi / Internet / Blynk, as well as by blocking task
in loop(), using delay() function as an example. The elapsed time then is very unaccurate

Why using ISR-based Hardware Timer Interrupt is better

Imagine you have a system with a mission-critical function, measuring water level and control the sump pump or doing something much more important. You normally use a software timer to poll, or even place the function in loop(). But what if another function is blocking the loop() or setup().

So your function might not be executed, and the result would be disastrous.

You’d prefer to have your function called, no matter what happening with other functions (busy loop, bug, etc.).

The correct choice is to use a Hardware Timer with Interrupt to call your function.

These hardware timers, using interrupt, still work even if other functions are blocking. Moreover, they are much more precise (certainly depending on clock frequency accuracy) than other software timers using millis() or micros(). That’s necessary if you need to measure some data requiring better accuracy.

Functions using normal software timers, relying on loop() and calling millis(), won’t work if the loop() or setup() is blocked by certain operation. For example, certain function is blocking while it’s connecting to WiFi or some services.

The catch is your function is now part of an ISR (Interrupt Service Routine), and must be lean / mean, and follow certain rules. More to read on:

HOWTO Attach Interrupt


Currently supported Boards

  1. ESP32-S2-based boards, such as ESP32_S2_DEV, ESP32_S2 Saola, etc

Important Notes about ISR

  1. Inside the attached function, delay() won’t work and the value returned by millis() will not increment. Serial data received while in the function may be lost. You should declare as volatile any variables that you modify within the attached function.

  2. Typically global variables are used to pass data between an ISR and the main program. To make sure variables shared between an ISR and the main program are updated correctly, declare them as volatile.



Changelog

Releases v1.3.0

  1. Initial coding to support ESP32-S2
  2. Sync with ESP32TimerInterrupt library v1.3.0

Examples

  1. Argument_None
  2. Change_Interval
  3. ISR_RPM_Measure
  4. ISR_Switch
  5. ISR_Timer_4_Switches
  6. ISR_Timer_Complex
  7. ISR_Timer_Switch
  8. ISR_Timer_Switches
  9. RPM_Measure
  10. SwitchDebounce
  11. TimerInterruptTest

Example Change_Interval on ESP32_S2_DEV

The following is the sample terminal output when running example Change_Interval to demonstrate how to change Timer Interval on-the-fly

Starting Change_Interval on ESP32S2_DEV
ESP32_S2_TimerInterrupt v1.3.0
CPU Frequency = 240 MHz
[TISR] ESP32_S2_TimerInterrupt: _timerNo = 0 , _fre = 1000000
[TISR] TIMER_BASE_CLK = 80000000 , TIMER_DIVIDER = 80
[TISR] _timerIndex = 0 , _timerGroup = 0
[TISR] _count = 0 - 2000000
[TISR] timer_set_alarm_value = 2000000.00
ITimer0: millis() = 720
Starting  ITimer0 OK, millis() = 724
[TISR] ESP32_S2_TimerInterrupt: _timerNo = 1 , _fre = 1000000
[TISR] TIMER_BASE_CLK = 80000000 , TIMER_DIVIDER = 80
[TISR] _timerIndex = 1 , _timerGroup = 0
[TISR] _count = 0 - 5000000
[TISR] timer_set_alarm_value = 5000000.00
ITimer1: millis() = 746
Starting  ITimer1 OK, millis() = 749
ITimer0: millis() = 2715
ITimer0: millis() = 4715
ITimer1: millis() = 5741
ITimer0: millis() = 6715
ITimer0: millis() = 8715
Time = 10001, Timer0Count = 5, Timer1Count = 2
ITimer0: millis() = 10715
ITimer1: millis() = 10741
ITimer0: millis() = 12715
ITimer0: millis() = 14715
ITimer1: millis() = 15741
ITimer0: millis() = 16715
ITimer0: millis() = 18715
Time = 20002, Timer0Count = 10, Timer1Count = 4
[TISR] ESP32_S2_TimerInterrupt: _timerNo = 0 , _fre = 1000000
[TISR] TIMER_BASE_CLK = 80000000 , TIMER_DIVIDER = 80
[TISR] _timerIndex = 0 , _timerGroup = 0
[TISR] _count = 0 - 4000000
[TISR] timer_set_alarm_value = 4000000.00
[TISR] ESP32_S2_TimerInterrupt: _timerNo = 1 , _fre = 1000000
[TISR] TIMER_BASE_CLK = 80000000 , TIMER_DIVIDER = 80
[TISR] _timerIndex = 1 , _timerGroup = 0
[TISR] _count = 0 - 10000000
[TISR] timer_set_alarm_value = 10000000.00
Changing Interval, Timer0 = 4000,  Timer1 = 10000
ITimer0: millis() = 24011
ITimer0: millis() = 28011
Time = 30003, Timer0Count = 12, Timer1Count = 4
ITimer1: millis() = 30031
ITimer0: millis() = 32011
ITimer0: millis() = 36011