ESP_TIMER

1. ESP_TIMER Overview

ESP_TIMER is a high-precision software timer API provided by ESP-IDF, implemented based on a 64-bit hardware timer with microsecond resolution. Callbacks are executed in a separate Timer Task (not ISR context), allowing the use of Serial.print, which is much more convenient than hardware timer ISRs. This experiment creates a periodic timer that triggers every second, printing the trigger count in the callback.

Typical Application Scenarios:

2. Core Concepts

2.1 esp_timer vs Hardware Timer

2.2 Key APIs

esp_timer_create(&args, &handle) — Creates a timer.

const esp_timer_create_args_t timer_args = {
    .callback = esp_timer_callback,      // Callback function pointer
    .name = "Esp_Timer",                  // Debug name
    // .dispatch_method defaults to ESP_TIMER_TASK → callback runs in timer task
};
esp_timer_handle_t timer_handle;
esp_timer_create(&timer_args, &timer_handle);

esp_timer_start_periodic(handle, period_us) — Starts a periodic timer. period_us is in microseconds, 1000000 = 1 second. The timer can be stopped at any time using esp_timer_stop() after creation.

2.3 volatile for Cross-Task Variables

The callback executes in the Timer Task, while loop() executes in the Arduino Task. Shared variables between different tasks require the volatile modifier, otherwise the compiler may cache the variable in each task's CPU registers, causing stale values to be read.

3. Hardware Dependencies

This project is a pure software experiment with no external hardware required. Only a USB cable is needed to connect to the serial port for viewing output.

4. Project Architecture and Flow

​x
setup()
  ├─ Serial.begin(115200)              // Initialize serial port
  ├─ esp_timer_create(&args, &handle)  // Create timer
  └─ esp_timer_start_periodic(handle, 1000000) // Start: 1s period

loop()                                 // Empty loop
  └─ (Timer callback runs independently in background Timer Task)

[Timer Task Background]
  └─ esp_timer_callback()              // Called automatically every second
       ├─ trigger_count++              // Increment counter
       └─ Serial.printf(...)           // Print trigger info

5. Source Code Details

Complete source code: Source Code → Arduino → 1.Basic Peripherals → 4.ESP_TIMER → 4.ESP_TIMER.ino

5.1 Global Variables

trigger_count is written in the callback and read in loop() (if needed). Cross-task sharing requires volatile.

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volatile uint32_t trigger_count = 0;   // Timer trigger count counter

If loop() doesn't need to read this variable, volatile can be omitted, but keeping it is good practice for future extensibility.

5.2 Timer Callback Function

The callback runs in the Timer Task, not ISR, so Serial.printf is safe to use.

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void esp_timer_callback(void* arg) {
    trigger_count++;
    Serial.printf("Trigger count: %u | Current time: %lu ms\n", trigger_count, millis());
}

5.3 setup() — Create and Start Timer

First configure the esp_timer_create_args_t structure, then create the timer, and finally start it.

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void setup() {
    Serial.begin(115200);
    Serial.println("ESP_TIMER Started (1000ms Period)");

    const esp_timer_create_args_t timer_args = {
        .callback = esp_timer_callback,
        .name = "Esp_Timer"
    };

    esp_timer_handle_t timer_handle;
    esp_timer_create(&timer_args, &timer_handle);
    esp_timer_start_periodic(timer_handle, 1000000);  // 1,000,000 us = 1s
}

void loop() {}  // Empty loop — all work done by timer callback

loop() is empty because there is no polling logic needed. The timer runs independently in the background with callbacks triggering automatically, which is the perfect example of event-driven programming.

6. Operation Flow

6.1 Build and Flash

Arduino flash process: See Arduino → 1. Before Development → 2. Build and Flash.

6.2 Expected Behavior

Open the Serial Monitor (115200 bps) and one line is printed every second:

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====================================
ESP_TIMER Started (1000ms Period)
====================================
Trigger count: 1 | Current time: 1026 ms
Trigger count: 2 | Current time: 2026 ms
Trigger count: 3 | Current time: 3026 ms
Trigger count: 4 | Current time: 4026 ms
...

6.3 Verification Methods

7. Common Issues