ESP Arduino playing with peripherals (V) basic concept of interrupt and timer interrupt

1. Embedded development requires a deep understanding “ Limited resources ”

The main technical contradiction of embedded system design and development ： Chip and board level resource constraints VS. Real time requirements for task and event processing

Memory ,Flash Space ,GPIO Number , ADC/DAC Number of channels, etc , Even the volume , Power waste , Embedded systems face many constraints , From the perspective of demand, the system requires timely processing , Fast response and low power consumption are better ...... wait , This pair of contradictions gave birth to the core technologies of various embedded systems , Low power consumption and power saving 、 Real-time operating system 、 High speed serial port ...... All to solve the above technical contradictions .

2. For god horse to have interruption mechanism ？

The main program of the embedded system mentioned above is basically a big cycle , If the request of each task is to be processed in the loop , The roughest way is to take turns to query , Polling for short , Polling can solve the problems of simple systems , But when the number of requests and processing complexity increase , It's hard to avoid , Interruption is to solve “ Distribute on demand ” Resource allocation problem . Let's take a look at a picture ：

 

3. Basic concept and processing flow of interruption

• Text definition of interruption ： Means when there is a need ,CPU Temporarily stop the execution of the current program and execute the program and execution process dealing with the new situation .
           In the process of program running , There is a system that must be created by CPU Immediate situation , here ,CPU The process of temporarily suspending the execution of a program to deal with this new situation is called interruption .

The basic processing flow is clear from the following figure

4. Three elements of interrupt processing

         • Trigger Conditions （ type / Channel configuration, etc , The process is initialization ）

• Interrupt vector （ interrupt entrance / Handle --- Hook to the corresponding execution position ）

• interrupt operation （ Interrupt handling function ）

5. With Timer Take interruption as an example , Is the easiest to understand , Set up an alarm clock , When the time comes “ work ”

Look at it ESP32-Arduino From the application of the platform, we can see various types of interrupts  , Other external interrupts , Abnormal interruption, etc. expand in another article , Examples include the following applications ：

*Alarm Type timed interrupt

* Set the clock running in the background “ Tick tock ”, Deal with different tasks according to the beat （ticker）

*RTC Real time clock , Provide a clock that is aligned and synchronized with the real world （ Specific date , Minutes and seconds ）

*WDT watchdog

6. The sample code

Case study 1-----Timer-sample1 Timed interrupt

#define LED_ON LOW;
#define LED_OFF HIGH;

hw_timer_t *timer=NULL;
uint32_t flag=0;
static void IRAM_ATTR Timer0_CallBack(void);
const int led=22;
int ledState=LED_OFF;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  pinMode(led, OUTPUT);
  timer=timerBegin(0,80,true);
  timerAttachInterrupt(timer,Timer0_CallBack,true);
  timerAlarmWrite(timer,1000000,true); //  Company us, Timing mode 
  timerAlarmEnable(timer); //  Start timer 

}

void loop() {
  // put your main code here, to run repeatedly:
  if(flag){
    flag=0;
    Serial.println("time out. ");  //  Serial port printing only requires monitoring , Non time sensitive 
    
    
    }

}

static void IRAM_ATTR Timer0_CallBack(void){
  flag=1;
  ledState=!ledState;  //  Controlling flashing lights is a time sensitive task 
  digitalWrite(led,ledState);
  }

Case study 2----- Use clock ticking to deal with multitasking

#include <Arduino.h>
#include <Ticker.h>

// attach a LED to pPIO 21
#define LED_PIN 21

Ticker blinker;
Ticker toggler;
Ticker changer;
float blinkerPace = 0.1;  //seconds
const float togglePeriod = 5; //seconds

void change() {
  blinkerPace = 0.5;
}

void blink() {
  digitalWrite(LED_PIN, !digitalRead(LED_PIN));
}

void toggle() {
  static bool isBlinking = false;
  if (isBlinking) {
    blinker.detach();
    isBlinking = false;
  }
  else {
    blinker.attach(blinkerPace, blink);
    isBlinking = true;
  }
  digitalWrite(LED_PIN, LOW);  //make sure LED on on after toggling (pin LOW = led ON)
}

void setup() {
  pinMode(LED_PIN, OUTPUT);
  toggler.attach(togglePeriod, toggle);
  changer.once(30, change);
}

void loop() {
  
}

Case study 3--RTC Real time clock

Learn how to be arduino Get library support in

Tools -> Management of the library -> Search for “ESP32TIME”-> install

And then in “ Example ” Open the corresponding example in OK 了 . Here we use an example to illustrate the simplest call

/*
esp32time sample
*/

#include <ESP32Time.h>

ESP32Time rtc;

void setup() {
  Serial.begin(115200);
  rtc.setTime(30, 24, 15, 17, 1, 2022);  // 17th Jan 2022 15:24:30
}

void loop() {
//  Serial.println(rtc.getTime());          //  (String) 15:24:38
//  Serial.println(rtc.getDate());          //  (String) Sun, Jan 17 2021
//  Serial.println(rtc.getDate(true));      //  (String) Sunday, January 17 2021
//  Serial.println(rtc.getDateTime());      //  (String) Sun, Jan 17 2021 15:24:38
//  Serial.println(rtc.getDateTime(true));  //  (String) Sunday, January 17 2021 15:24:38
//  Serial.println(rtc.getTimeDate());      //  (String) 15:24:38 Sun, Jan 17 2021
//  Serial.println(rtc.getTimeDate(true));  //  (String) 15:24:38 Sunday, January 17 2021
//
//  Serial.println(rtc.getMicros());        //  (long)    723546
//  Serial.println(rtc.getMillis());        //  (long)    723
//  Serial.println(rtc.getEpoch());         //  (long)    1609459200
//  Serial.println(rtc.getSecond());        //  (int)     38    (0-59)
//  Serial.println(rtc.getMinute());        //  (int)     24    (0-59)
//  Serial.println(rtc.getHour());          //  (int)     3     (0-12)
//  Serial.println(rtc.getHour(true));      //  (int)     15    (0-23)
//  Serial.println(rtc.getAmPm());          //  (String)  pm
//  Serial.println(rtc.getAmPm(true));      //  (String)  PM
//  Serial.println(rtc.getDay());           //  (int)     17    (1-31)
//  Serial.println(rtc.getDayofWeek());     //  (int)     0     (0-6)
//  Serial.println(rtc.getDayofYear());     //  (int)     16    (0-365)
//  Serial.println(rtc.getMonth());         //  (int)     0     (0-11)
//  Serial.println(rtc.getYear());          //  (int)     2021

  Serial.println(rtc.getTime("%A, %B %d %Y %H:%M:%S"));   // (String) returns time with specified format 
  // formating options  http://www.cplusplus.com/reference/ctime/strftime/


  struct tm timeinfo = rtc.getTimeStruct();
  Serial.println(&timeinfo, "%A, %B %d %Y %H:%M:%S");   //  (tm struct) Sunday, January 17 2021 07:24:38
  
  delay(1000);
}