Maximum Reload time for WDT

[Shagan]

Hi Guys, 

We have a need to send data every 4 hours. 

In order to do this, we sleep 1 hour at a time (1-hour timer - single shot) and increment counter, and when the count is 4 we send the data. This is working well. 

Due to unknown reasons the device sometimes can get hung when trying to send the data. 

Our plan was to set the WDT_CONFIG_RELOAD_VALUE to 120000000, to make sure we reset the device after 1 hour if it got stuck. 

But we are unable to provide values more than 600000 (which triggers at 100 seconds). 

Can u suggest a way to configure such a large interval? 

regards

Shankar

[deknoob]

Hi Stian,

I am actually using nRF52833 which doesn't have ULP mode. Best result is 1.4uA when I select LFXO. As you can see I use 1000 second WDT reload timeout, to enable longer startup time for LFXO. But I don't see variation if I wait for longer. With RC oscillator I am measuring 1.9uA.

I use NRF Power Profiler for measurement, VDD is 3V. 

Is this the best I can get with 52833? Or maybe my consumption is higher because of process variation?

1.4uA is still an improvement compared to 2.3uA sleep current measured in the past when I simply use timer to wakeup and with full RAM retention

    NRF_CLOCK->LFCLKSRC = 1; // LFXO
    //NRF_CLOCK->LFRCMODE = 1; // ULP mode
    //NRF_CLOCK->LFCLKSRC            = (CLOCK_LFCLKSRC_SRC_RC << CLOCK_LFCLKSRC_SRC_Pos);

    NRF_CLOCK->TASKS_LFCLKSTART = 1; // Start LF clock
    while(!NRF_CLOCK->EVENTS_LFCLKSTARTED){
    }
    NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
    NRF_WDT->CRV = 32768000; // WDT wakeup every 100 sec
    NRF_WDT->TASKS_START = 1; // start WDT
    for(int i = 0; i < 8; i++){
        NRF_POWER->RAM[i].POWERCLR = 0x3; // Turn off RAM block 0-7
    }
    NRF_POWER->RAM[8].POWERCLR = 0x3F; // Turn off RAM block 8
    
    for(;;){
        __WFE();
    }

[Stian Røed Hafskjold]

Hi, the base current is a little bit higher on 833.

ION_RAMOFF_EVENT

System ON, no RAM retention, wake on any event

1.1

µA

So 1.1 + .23 = 1.33 uA, which is the expected typical current. And yes, if you get higher (or lower) current it's because of process variation.