NUCLEO_L476RG: Measuring ADC_TEMP after using ADC_VREF in AnalogIn results in abnormal results

[maskedw]

Description

• Type: Bug
• Related issue: STM32 HAL issue - reading internal temp after VBAT measurement. #1685, STM32F4xx: Using AnalogIn() for internal VBAT and TEMP measurements #4326, NUCLEO_L476RG AnalogIn, want to measure internal temperature sensor. #6397

---

Bug

Target
NUCLEO_L476RG

Toolchain:
GCC_ARM

Toolchain version:
arm-none-eabi-gcc 6.3.1

mbed-cli version:
1.2.2

mbed-os sha:
16bac10

Steps to reproduce
(Room temperature 23 ℃)

#include "mbed.h"

Serial pc(USBTX, USBRX);

int main()
{
    pc.baud(115200);
    while(1)
    {
        {
            AnalogIn adc_temp(ADC_TEMP);
            wait_ms(1000);
            int16_t temp12 = adc_temp.read_u16() >> 4;
            int32_t temp = __LL_ADC_CALC_TEMPERATURE(3300, temp12, LL_ADC_RESOLUTION_12B);
            printf("TMP: %d\n", temp);
        }
    }

    return 0;
}

This measured value is not as expected, but I have posted another issue. #6397

TMP: 30

#include "mbed.h"

Serial pc(USBTX, USBRX);

int main()
{
    pc.baud(115200);
    while(1)
    {
        {
            AnalogIn adc_vref(ADC_VREF);
            wait_ms(1000);
            uint16_t vref12 = adc_vref.read_u16() >> 4;
            int vref = (3.0f * (*VREFINT_CAL_ADDR) / vref12 * 1000);
            printf("AVDD: %d\n", vref);
        }

        {
            AnalogIn adc_temp(ADC_TEMP);
            wait_ms(1000);
            int16_t temp12 = adc_temp.read_u16() >> 4;
            int32_t temp = __LL_ADC_CALC_TEMPERATURE(3300, temp12, LL_ADC_RESOLUTION_12B);
            printf("TMP: %d\n", temp);
        }
    }

    return 0;
}

After measuring VREFINT, obviously an abnormal value will be returned.

TMP: -205
AVDD: 3306

[0xc0170]

@ARMmbed/team-st-mcd Please review

[jeromecoutant]

Hi
Issue is confirmed. ADC driver team is contacted.
Thx

[jeromecoutant]

ST_INTERNAL_REF 45122

[maskedw]

With #6412 change, we confirmed that both ADC_VREF and ADC_TEMP can be measured normally.