// Listing 3.1 — General Purpose Timer LED Blink 

#include <stdio.h> 

#include "driver/gpio.h" 

#include "driver/timer.h" 

#include "freertos/FreeRTOS.h" 

#include "freertos/task.h" 

 

#define LED_GPIO      6 

#define TIMER_GROUP_USED  TIMER_GROUP_0 

#define TIMER_IDX_USED   TIMER_0 

#define APB_CLK_HZ     80000000UL     // Typical APB clock on ESP32-S3 

#define TIMER_DIVIDER    80         // Prescalar 80. So, APB/80 -> 1 MHz timer tick (1 tick = 1 us) 

 

// Blink period in microseconds 

#define BLINK_PERIOD_US   1000000UL     // 1,000,000 us = 1 second 

 

// --- ISR callback (called automatically at each alarm) --- 

static bool IRAM_ATTR timer_isr_cb(void *args); 

 

void app_main() 

{ 

  // Configure LED pin 

  gpio_reset_pin(LED_GPIO); 

  gpio_set_direction(LED_GPIO, GPIO_MODE_OUTPUT); 

  gpio_set_level(LED_GPIO, 0); 

 

  // 1) Configure timer 

  timer_config_t tcfg = { 

    .divider   = TIMER_DIVIDER, 

    .counter_dir = TIMER_COUNT_UP, 

    .counter_en = TIMER_PAUSE,   // start paused; we'll start after setup 

    .alarm_en  = TIMER_ALARM_EN, 

    .auto_reload = true       // periodic alarm (repeats automatically) 

  }; 

  timer_init(TIMER_GROUP_USED, TIMER_IDX_USED, &tcfg); // tcfg is the initialized timer instance 

 

  // Calculate the alarm tick count with this formula (works for any divider): ticks per us = [APB clock frequency / (Divider * 1000000)] 

  const uint64_t alarm_ticks = 

    ((uint64_t)BLINK_PERIOD_US * (uint64_t)APB_CLK_HZ) / 

    ((uint64_t)TIMER_DIVIDER * 1000000ULL); 

 

  // 2) Reset the Counter to initialize the counter to 0 

  timer_set_counter_value(TIMER_GROUP_USED, TIMER_IDX_USED, 0); 

 

  // 3) Set the alarm value using alarm_ticks 

  timer_set_alarm_value(TIMER_GROUP_USED, TIMER_IDX_USED, alarm_ticks); 

 

  // 4) Enable the Alarm 

  timer_set_alarm(TIMER_GROUP_USED, TIMER_IDX_USED, TIMER_ALARM_EN); 

 

  // 5) Attach ISR callback 

  timer_isr_callback_add(TIMER_GROUP_USED, TIMER_IDX_USED, 

             timer_isr_cb, NULL, 0); 

 

  // 6) Start timer 

  timer_start(TIMER_GROUP_USED, TIMER_IDX_USED); 

 

  // Main task is free to do other work (the LED blink is fully hardware-timed) 

  while (1) { 

    printf("Main task alive. LED blinks via timer ISR.\n"); 

    vTaskDelay(pdMS_TO_TICKS(1000)); // periodic debug printing 

  } 

} 

 

// --- ISR callback (called automatically at each alarm) --- 

static bool IRAM_ATTR timer_isr_cb(void *args) 

{ 

  static bool level = false; 

  level = !level; 

  gpio_set_level(LED_GPIO, level); // Toggle LED 

  return false; 

}