Andrew Starr

Important changes to forums and questions

All forums and questions are now archived. To start a new conversation or read the latest updates go to forums.mbed.com.

7 years, 5 months ago.

xDot ADC problem when coming out of sleep mode

Hi there,

I have a function that reads 3 ADC pins: PA_4, PA_5 and PB_0. This function is called periodically, in between calls to sleep();

The analogue inputs are declared as follows:

AnalogIn ain0(PA_4); AnalogIn ain1(PA_5); AnalogIn ain2(PB_0);

They are read in the called function as follows:

analogue[0].raw = ain0.read(); analogue[1].raw = ain1.read(); analogue[2].raw = ain2.read();

The initial call (before the first sleep()) returns valid ADC readings. After the first sleep(), subsequent reads of the ADCs return 0.000000V.

Sleep() call is as follows:

dot->sleep(10, mDot::RTC_ALARM, false);

Note: the code is built with libxDot-Custom (this application requires the AS923 custom channel plan).

Does anyone have a fix for this?

Thanks very much!

Hi, I have the same problem. Notice that if you use deep sleep, the problem is not occurring.

I thought initially that was something wrong with sleep_save_io/sleep_restore_io https://developer.mbed.org/teams/MultiTech/code/Dot-Examples/file/f8c29f84178b/examples/src/dot_util.cpp

But it seems there is something wrong with the `sleep` method. https://developer.mbed.org/teams/MultiTech/code/libxDot-dev-mbed5/file/28f05671c7f1/mDot.h

I'm using this libxDot: https://developer.mbed.org/teams/MultiTech/code/libxDot-mbed5/#5351293b3c55

Going to check with the latest version and report back.

posted by Lucian Corduneanu 20 Jul 2017

Tested with the latest dev lib https://developer.mbed.org/teams/MultiTech/code/libxDot-dev-mbed5/rev/28f05671c7f1

And mbed-os 5.4.7 https://github.com/ARMmbed/mbed-os/#fc1836545dcc2fc86f03b01292b62bf2089f67c3

The same problem! :(

posted by Lucian Corduneanu 20 Jul 2017

1 Answer

Lucian Corduneanu
7 years, 4 months ago.

Oh, it seems like reseting the HSI clock did the trick. https://developer.mbed.org/questions/78300/xDot-ADC-problem-when-coming-out-of-slee/

However wouldn't be a good idea to add this piece of code to the utils examples?

// Enable the HSI (to clock the ADC)
RCC_OscInitTypeDef RCC_OscInitStruct;
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
RCC_OscInitStruct.HSIState       = RCC_HSI_ON;
RCC_OscInitStruct.PLL.PLLState   = RCC_PLL_NONE;
HAL_RCC_OscConfig(&RCC_OscInitStruct);

Accepted Answer