WDT triggered too early

Question

Hi everyone, 
 
 I'm using nrf52840 custom board (pca10056) 
 SDK version: 15.3 
 OS: Fedora 
 
 I work on a custom board and try to use WDT like so in the WTD project example: 
 int main(void)
{
 uint32_t err_code = NRF_SUCCESS;

 //BSP configuration for button support: button pushing will feed the dog.
 err_code = nrf_drv_clock_init();
 APP_ERROR_CHECK(err_code);
 nrf_drv_clock_lfclk_request(NULL);

 err_code = app_timer_init();
 APP_ERROR_CHECK(err_code);

 // err_code = bsp_init(BSP_INIT_BUTTONS, bsp_event_callback);
 // APP_ERROR_CHECK(err_code);

 //Configure all LEDs on board.
 // bsp_board_init(BSP_INIT_LEDS);
 nrf_gpio_cfg_output(RLED);
 nrf_gpio_cfg_output(GLED);
 nrf_gpio_cfg_output(BLED);
 nrf_gpio_pin_set(RLED);
 nrf_gpio_pin_set(GLED);
 nrf_gpio_pin_set(BLED);

 //Configure WDT.
 nrf_drv_wdt_config_t config = NRF_DRV_WDT_DEAFULT_CONFIG;
 config.behaviour = NRF_WDT_BEHAVIOUR_RUN_HALT;
 config.reload_value = 360000;
 err_code = nrf_drv_wdt_init(&config, wdt_event_handler);
 APP_ERROR_CHECK(err_code);
 err_code = nrf_drv_wdt_channel_alloc(&m_channel_id);
 APP_ERROR_CHECK(err_code);
 nrf_drv_wdt_enable();

 //Indicate program start on LEDs.
 // for (uint32_t i = 0; i < LEDS_NUMBER; i++)
 // { nrf_delay_ms(200);
 // bsp_board_led_on(i);
 // }
 // err_code = bsp_buttons_enable();
 // APP_ERROR_CHECK(err_code);

 nrf_delay_ms(2000);

 led_on(GLED);

 while (1) {
 // __SEV();
 // __WFE();
 // __WFE();
 }
} 
 When I set the reload value to 10 000ms my WDT is triggered every 10s but when I try 360 000ms (6min) it's triggered approximately at 1min and 30s only... 
 What am I doing wrong?

Otso Jousimaa · Accepted Answer

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);

WDT triggered too early

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