Basic mechanism of running examples for power efficiency

[Senchoi]

I'm quite new to nrf.

These days I'm trying to program power efficient uart data sender over ble.

It receives uart and sends data fine.

The problem is it's not going into sleep mode properly and consumes about 883uA or 544uA(DCDC mode) on idle.

But what I'm trying to understand is not just making this project into ultra low power uart data sender perfectly.

I'm trying to understand basic structure.

Even if I run ble_app_beacon example, I wonder why advertising signal repeats when the code is not in a for loop or while loop or a thread starter.

The beacon code looks like this

int main(void)
{
    // Initialize.
    log_init();
    timers_init();
    leds_init();
    power_management_init();
    ble_stack_init();
    advertising_init();

    // Start execution.
    NRF_LOG_INFO("Beacon example started.");
    advertising_start();

    // Enter main loop.
    for (;; )
    {
        idle_state_handle();
    }
}

as you can see, only the idle_state_handle is in the loop.

So when beacon app is not going into sleep mode between advertising signals,

I would imagine I'd have to look into other repeating commands like for loop or while loop but there's no such thing other than idle_state_handle which merely calls sd_app_evt_wait() so it can go to sleep mode.

in the uart project I'm working on, when the programmed nrf52840 dongle connects to the other device over ble,

It is also programmed to send received data from arduino(UART data) to the other dongle which sends received data to usb so I can check the data in the PC

This also doesn't go to sleep in between sending uart signals.

So I would also imagine I'd have to go into uart data sending function like uart_event_handle() but there is no for,while loop in this or thread starter for that matter.

So how should I debug similar projects?

I'm guessing there must be some order that I can understand so I could pin-point which spot(code) is causing excessive power consumption

or what I have to do before putting it into sleep mode.

[Hung Bui]

Hi Senchoi, 

For measuring current consumption , I would suggest to test with the ble_app_pwr_profiling example. The example is optimized for low power consumption. 

Regarding the current you are seeing, it could be related to logging module, you may want to turn off any RTT or UART logging. 

[Senchoi]

it seems logging is already disabled by NRF_LOG_ENABLED 0 in sdk_config.h

Although I'm going to have to test ble_app_pwr_profiling. If it works I would have to migrate functions to this example.

[Hung Bui]

I guess it's the USB interface that consuming power. 
I'm not sure why you want to measure current consumption of a device that connect to USB port ? Are you planning to use it with battery ? 
I would suggest to measure current consumption on a DK instead of a dongle. 

[Senchoi]

USB is not connected. I'm using external power source after soldering sb1 and disconnecting sb2.

The product has to be quite small. That's why we use dongles.

And yes we're planning to use 3V battery.

Also I tried disabling uart in the for loop after reading this thread,

https://devzone.nordicsemi.com/f/nordic-q-a/367/handling-the-uart-when-sleeping

But the floor is still the same and high. Only uart signals are not getting sent.

So I guess I have to rule out uart's current consumption possibility.

[Senchoi]

When I comment out uart_init() entirely, idle current reaches the bottom.

But using app_uart_close() is not making any difference when I re-enable uart_init().

Is there a way to control the current consumption?

[Hung Bui]

Hi Senchoi, 

Which current consumption do you see after you call app_uart_close() ? Have you put the CPU to sleep ? 

I did a quick test here, with the uart example in \examples\peripheral\uart 

And I can see the current consumption dropped to a few uA after I click 'q' or 'Q'

I would suggest you to test with an empty application, with just the loop 

while (true)
{
__WFE();
__WFE();
__SEV();
// Do nothing.
}

To put the CPU to sleep to check if you can get to the bottom current. 

[Senchoi]

I tested with the code above at main function with nothing else in it.

although you can see some peaks, the average current is below 30nA and the tallest peak reaches below 12uA. So it's nearly zero current we can get by.

if I call app_uart_close() after uart_init() the current consumption is pretty much the same like below except it doesn't send uart data.

And this is the code for the current above.