Timer Interrupt

Example: Using a Timer to Trigger an Interrupt

#include "driver/timer.h"

#define TIMER_DIVIDER         16  // Timer divider
#define TIMER_SCALE           (TIMER_BASE_CLK / TIMER_DIVIDER)  // Timer scale
#define TIMER_INTERVAL_SEC    1  // Interval in seconds

void IRAM_ATTR onTimer(){
  Serial.println("Timer interrupt triggered!");
  // Add your timer interrupt handling code here
}

void setup() {
  Serial.begin(115200);

  // Configure timer 0
  timer_config_t config;
  config.divider = TIMER_DIVIDER;
  config.counter_dir = TIMER_COUNT_UP;
  config.counter_en = TIMER_START;
  config.autoreload = true;
  config.alarm_en = TIMER_ALARM_EN;
  config.intr_type = TIMER_INTR_LEVEL;
  timer_init(TIMER_GROUP_0, TIMER_0, &config);

  // Set timer alarm to trigger after the specified interval
  timer_set_alarm_value(TIMER_GROUP_0, TIMER_0, TIMER_INTERVAL_SEC * TIMER_SCALE);
  timer_enable_intr(TIMER_GROUP_0, TIMER_0);

  // Attach the interrupt to the timer
  timer_isr_register(TIMER_GROUP_0, TIMER_0, onTimer, NULL, ESP_INTR_FLAG_IRAM, NULL);

  // Start the timer
  timer_start(TIMER_GROUP_0, TIMER_0);
}

void loop() {
  // Main loop does nothing; the timer ISR takes care of the interrupt
}

Explanation:

• Timer Setup: The timer is configured with a divider, an interval, and an alarm.
• Interrupt Service Routine (ISR): The ISR onTimer() is triggered each time the timer alarm occurs (every 1 second in this example).
• ISR Handling: The ISR handles the interrupt and prints a message every time the timer interrupt is triggered.

Key Points to Consider:

1. Short ISR Functions: ISRs should be kept short and efficient because the main program is paused while the ISR runs. Avoid delays, Serial.print(), or long computations in the ISR.
2. Global Variables in ISR: Be cautious when modifying global variables inside an ISR. Use volatile for variables that are shared between the ISR and the main code to ensure proper synchronization.
3. Interrupt Priority: ESP32 has configurable interrupt priorities, allowing more important interrupts to preempt others.