5 years ago.

How to use sleep and/or low energy solutions

Here is a snip of some code I have been successfully using before all the changes on Mbed, its not complete but enough to explain the issue.

LowPowerTicker wakeup;

void callback(void) {
    wake = 1;
}

int main() {
    
    while(1){   
    
        advance_clock();
        
        while(second==lastsecond){
            gettime();
            }  
        lastsecond=second;        
        
        segmentDisplay.Number(displaydate);
        segmentDisplay.Write(displaytime);        
  
        wakeup.attach(callback,0.90f);
        wake = 0;
        while(!wake) sleep();                     
    }      
}

If I use early Mbed (version 2, revision 172) libraries it works exactly as I want it to.

however updating to the latest Mbed(2) the low power simply isn't, its normal running power. Okay, so try Mbed-os and exactly the same result.

After searching the Mbed API information, no luck, I still can not see how to get a simple non-RTOS low power solution.

This does work as it says on the tin both Mbed(2) and Mbed-os:

#include "mbed.h"
 
DigitalOut myled(LED1);
LowPowerTicker toggleTicker;

/**
* This is a callback! Do not call frequency-dependent operations here.
*
* For a more thorough explanation, go here: 
* https://developer.mbed.org/teams/SiliconLabs/wiki/Using-the-improved-mbed-sleep-API#mixing-sleep-with-synchronous-code
**/
void ledToggler(void) {
    myled = !myled;
}
 
int main() {
    toggleTicker.attach(&ledToggler, 0.2f);
    while(1) {
        sleep();
    }
}

However we all know you can only use minimal code in a ISR call back, so how can I set a flag to jump out of sleep mode and return to sleep when I have finished like I did before.

This question does extend to other platforms not only SiLabs EFM32

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Last updated: 23 Apr 2019

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