esp32 - simple poc demonstrating a timer interupt driven ISR living in a class

isr_in_class.ino

/* simple poc demonstrating a timer interupt driven ISR living in a class */

class foo {
    public:
        bool start_isr();

    private:
        static void _timer_isr();
        hw_timer_t * exampleTimer;

};

void IRAM_ATTR foo::_timer_isr() {
    ESP_LOGI(TAG, "from ISR - seconds since boot: %i", time(NULL));
}

bool foo::start_isr() {
    const uint8_t TIMER_NO = 0; /* 4 timers so 0-3 */
    if (exampleTimer) {
        ESP_LOGE(TAG, "hw timer %i already in use", TIMER_NO);
        return false;
    }
    exampleTimer = timerBegin(TIMER_NO, APB_CLK_FREQ / (1000 * 1000), true);  /* timer no: 0, prescaler calc results in 1 mHz clock res , timers counts up */
    
    if (!exampleTimer) {
        ESP_LOGE(TAG, "could not start timer %i", TIMER_NO);
        return false;
    }
    timerAttachInterrupt(exampleTimer, &_timer_isr, true);            /* true means timer repeats */

    const uint64_t ONE_SECOND = 1000000;
    timerAlarmWrite(exampleTimer, ONE_SECOND * 3, true);
    timerAlarmEnable(exampleTimer);
    return true;
}

foo foo;

void setup() {
    ESP_LOGI(TAG, "APB clock freq: %i", APB_CLK_FREQ);

    //RTC_APB_FREQ_REG
    foo.start_isr();
    foo.start_isr(); /* should give an error */
}

void loop() {
    // put your main code here, to run repeatedly:

}