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1 week, 4 days ago.

Lowest power consumption achievable w/ sleep manager in mbed OS 5.9

Wondering what is the lowest power consumption achievable with the sleep manager api in deep sleep? I have done some measurements on the NUCLEO F411RE board, just running the code below w/ mbed-os-5.9.4 and I'm seeing a little under 5 mA, both when deep sleep is enabled and locked. Is this expected? I'm measuring the current draw w/ a DMM across JP6. Is it possible to get into the tens or hundreds of micro amps w/ the sleep manager api?

Thanks, Evan

include the mbed library with this snippet

#include "mbed.h"

RawSerial pc(USBTX, USBRX);

int main()
{
    pc.baud(115200);

    while (true) {
        // Deep sleep for 1 second
        printf("Deep sleep allowed: %i\r\n", sleep_manager_can_deep_sleep());
        wait(5);

        // Lock deep sleep
        printf("Locking deep sleep\r\n");
        DeepSleepLock lock;

        // Sleep for 1 second
        printf("Deep sleep allowed: %i\r\n", sleep_manager_can_deep_sleep());
        wait(5);
    }
}

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1 Answer

4 days, 10 hours ago.

Hi Evan,

We see two issues with your example:

To enter deep sleep you can use Thread::wait() instead - which takes an argument in msec.

Here is an updated program we tested:

#include "mbed.h"

DeepSleepLock lock_out_sleep;

int main()
{

    while (true) {

        // allow deep sleep
        lock_out_sleep.unlock();

        // wait for 10 seconds
        Thread::wait(10000);

        // lock out deep sleep
        lock_out_sleep.lock();

        // wait for 10 seconds
        Thread::wait(10000);
    }

}

Using JP6 we see the current measurement toggle between 6.6mA and 1.9mA.

On Mbed 5.9.4 for deep sleep to be entered you need both MBED_TICKLESS and DEVICE_LPTICKER defined. You can do this through targets.json if building with the CLI or with the Compile Macros for the Online compiler (under the Compile menu).

Please try the example above and let us know what you measure. We don't know if this is the lowest achievable value as we aren't intimately familiar with this device. Next week we'll perform some additional research.

-Ralph, Team Mbed

Thanks Ralph, I replaced the wait w/ Thread::wait and was getting current draw toggling between 4.6 mA and 140 uA. Worked just the same with the way I had the locks set up relying upon RAII of the DeepSleepObject object to lock on construction and release on destruction.

Probably would be good to update the example @ https://os.mbed.com/docs/v5.9/reference/power-management.html to use Thread::wait as well.

Thanks, Evan

posted by Evan Hosseini 11 Aug 2018

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