Timer accuracy for micro seconds

MaximSh over 2 years ago

Hi,

i defined timer

K_TIMER_DEFINE(my_timer, my_timer_handler, NULL);

then i am starting the timer with configuration :

k_timer_start(&my_timer, K_USEC(500), K_USEC(500));

The issue that the

the handler prints log every 581.5 us instead of 500.

What can be the reason?or how to trigger some handler every 500 us

Thanks

Top Replies

Emil Lenngren over 2 years ago +1

If I were to perform a SPIM transaction exactly every 500 us, I would do the following. - Use one RTC compare register that publishes a DPPI event. - Use one TIMER peripheral configured to perform…
MaximSh over 2 years ago in reply to Emil Lenngren +1

Hi, I tested it without zephyr +/- like you suggested, it is working. Looks like integrations with zephyr is the issue.

Parents

0 MaximSh over 2 years ago

Still have issues if i use counter with timer0

i set alarm to 500 micro but after 2000 triggers that should print 1000(0.5*2000= 1000 mili) it prints

00> I: READ:1748
00> I: READ:1904
00> I: READ:1873
00> I: READ:1751
00> I: READ:1979
00> I: READ:1871
00> I: READ:1784
00> I: READ:1871

CONFIG_COUNTER=y

CONFIG_COUNTER_TIMER0=y

Here is my code:

#define THREAD_PRIORITY K_PRIO_PREEMPT(K_HIGHEST_APPLICATION_THREAD_PRIO)
#define TIMER DT_NODELABEL(timer0)
#define DELAY 500

Here is a k_thread_entry_t set_alarm

static void set_alarm(void)
{
    const struct device *const counter_dev = DEVICE_DT_GET(TIMER);
    int err;

    printk("Counter alarm sample\n\n");

    if (!device_is_ready(counter_dev))
    {
        printk("device not ready.\n");
        return;
    }

    counter_start(counter_dev);

    alarm_cfg.flags = 0;
    alarm_cfg.ticks = counter_us_to_ticks(counter_dev, DELAY);
    alarm_cfg.callback = test_counter_interrupt_fn;
    alarm_cfg.user_data = &alarm_cfg;

    err = counter_set_channel_alarm(counter_dev, ALARM_CHANNEL_ID,
                                    &alarm_cfg);
    printk("Set alarm in %u sec (%u ticks)\n",
           (uint32_t)(counter_ticks_to_us(counter_dev,
                                          alarm_cfg.ticks) /
                      USEC_PER_SEC),
           alarm_cfg.ticks);

    if (-EINVAL == err)
    {
        printk("Alarm settings invalid\n");
    }
    else if (-ENOTSUP == err)
    {
        printk("Alarm setting request not supported\n");
    }
    else if (err != 0)
    {
        printk("Error\n");
    }
    while (1)
    {
        static uint16_t c = 0;
        k_sem_take(&timer_semaphore, K_FOREVER);
        static int64_t time = 0;
        if (c == 2000)
        {
            LOG_INF("READ:%lld", k_uptime_delta(&time));
            c = 0;
        }
        if ((c++ % 2) == 0)
        {

            struct acc_event *event = new_acc_event();
            EVENT_SUBMIT(event);
        }
    }
}

callback that give semaphore to thread loop

static void test_counter_interrupt_fn(const struct device *counter_dev,
                                      uint8_t chan_id, uint32_t ticks,
                                      void *user_data)
{
    struct counter_alarm_cfg *config = user_data;
    uint32_t now_ticks;
    uint64_t now_usec;
    int now_sec;
    int err;

    k_sem_give(&timer_semaphore);

  

    err = counter_set_channel_alarm(counter_dev, ALARM_CHANNEL_ID,
                                    user_data);
    if (err != 0)
    {
        printk("Alarm could not be set\n");
    }
}

What is wrong?

Thanks

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