RE: WDT triggered too early

awneil — Wed, 24 Jul 2019 10:52:37 GMT

[quote userid="80791" url="~/f/nordic-q-a/50147/wdt-triggered-too-early/200251"]why do I need to modify the SDK to fix this issue[/quote]

Because, as Otso Jousimaa explained, the issue is due to a bug in the SDK!

RE: WDT triggered too early

Louis Hatte — Wed, 24 Jul 2019 10:27:35 GMT

Hi Otso,

Now it works but why do I need to modify the SDK to fix this issue?

Is there no better way to resolve this problem?

Regards,

Louis

RE: WDT triggered too early

Otso Jousimaa — Tue, 23 Jul 2019 15:37:27 GMT

Hello,

You're not doing anything wrong. The SDK15.3 watchdog init function is here:

nrfx_err_t nrfx_wdt_init(nrfx_wdt_config_t const * p_config,
                         nrfx_wdt_event_handler_t  wdt_event_handler)
{
    NRFX_ASSERT(p_config);
    nrfx_err_t err_code;

#if !NRFX_CHECK(NRFX_WDT_CONFIG_NO_IRQ)
    NRFX_ASSERT(wdt_event_handler != NULL);
    m_wdt_event_handler = wdt_event_handler;
#else
    NRFX_ASSERT(wdt_event_handler == NULL);
    (void)wdt_event_handler;
#endif
    if (m_state == NRFX_DRV_STATE_UNINITIALIZED)
    {
        m_state = NRFX_DRV_STATE_INITIALIZED;
    }
    else
    {
        err_code = NRFX_ERROR_INVALID_STATE;
        NRFX_LOG_WARNING("Function: %s, error code: %s.",
                         __func__,
                         NRFX_LOG_ERROR_STRING_GET(err_code));
        return err_code;
    }

    nrf_wdt_behaviour_set(p_config->behaviour);

    nrf_wdt_reload_value_set((p_config->reload_value * 32768) / 1000);

#if !NRFX_CHECK(NRFX_WDT_CONFIG_NO_IRQ)
    NRFX_IRQ_PRIORITY_SET(WDT_IRQn, p_config->interrupt_priority);
    NRFX_IRQ_ENABLE(WDT_IRQn);
#endif

    err_code = NRFX_SUCCESS;
    NRFX_LOG_INFO("Function: %s, error code: %s.", __func__, NRFX_LOG_ERROR_STRING_GET(err_code));
    return err_code;
}

the nrfx_wdt_config_t->reload_value is uint32_t.

When you set the reload to 360 000, it gets multiplied by 32768 which is 11 796 480 000 and the uint32_t overflows.

As a fix convert the reload_value to uint64_t before multiplication:

  if((((uint64_t) p_config->reload_value * 32768) / 1000) >
      UINT32_MAX)  // Check for overflow
  {
    return NRF_ERROR_INVALID_PARAM;
  }

  nrf_wdt_reload_value_set(((uint64_t) p_config->reload_value * 32768) / 1000);