[HELP] ESP32-S3 Don't work ADC

[shizacat]

Description

Hello. I trying to read value from ADC, but have something problem.

1. Added this code, without it don't get anything. It always returns the same value, regardless of the applied voltage to the pin.

  /* Select RTC control */
  regval = getreg32(SENS_SAR_MEAS1_MUX_REG);
  regval &= ~(SENS_SAR1_DIG_FORCE_M);
  // regval |= (0 << SENS_SAR1_DIG_FORCE_S);  // 1: Select digital control; 0: Select RTC control.
  putreg32(regval, SENS_SAR_MEAS1_MUX_REG);

in here: https://github.com/apache/nuttx/blob/master/arch/xtensa/src/esp32s3/esp32s3_adc.c#L441

2. After, I got the value from ADC, but happed something strange, the voltage on pin drop down.
   I understand what happen. Please help!

Board: ESP32-S3 dev kit

Board connect

The voltage on pin before read.

The voltage on pin after read.

Configuration: ./tools/configure.sh -m esp32s3-devkit:adc

Console

# on pin 3V before read
nsh> adc -n 2
Sample:
1: channel: 0 value: 1727
Sample:
1: channel: 0 value: 1534
nsh>

Verification

• I have verified before submitting the report.

[acassis]

@shizacat thanks for finding this issue and reporting it here! @tmedicci @fdcavalcanti @eren-terzioglu

[fdcavalcanti]

Thanks for the report. I'll look into this.

[fdcavalcanti]

@shizacat Please share what NuttX version you are running.

• Does the voltage issue happen on other pins?
• It goes low only during reading or does it go back up again, after you are done sampling?

[shizacat]

@fdcavalcanti
NuttX version: 12.7.0

Does the voltage issue happen on other pins?

Yes, I tested on ADC Channel 0,1,2, the voltage behavior on the pin was the same.

It goes low only during reading or does it go back up again, after you are done sampling?

It stays low while the device is open.

Steps:

• Restart device, the voltage on pin ch0 is set to 3 V.
• call 'adc -p /dev/adc0 -n 5', in this moment voltage drop down to 1.4V, and it remains in this state. I can slight change the voltage on pin by resistor (but don't to zero).
• then I open the next device (old, as I think is closed). call 'adc -p /dev/adc1 -n 5', The voltage in channel 0 rises again to 3 V, and I can change it in the range from 0 to 3 V. But on channel 1 the voltage drop down to 1.4V
• the same is true for Channel 2

[fdcavalcanti]

@shizacat thanks. I did a quick test here without your RTC control modifications.

The voltage is indeed returning a bad value. If I hold the ADC pin to 3v3 or GND I can see it changes 1 or 2 mV, which is not ok. Maybe some bad equation or calibration related? Also, measured with a voltmeter and it is not dropping as you showed.

The difference when using the RTC code you suggested is that maybe something is not being properly shutdown, and it is externalizing that 1.4 V value, which is different than halving the input voltage. Weird anyway.

Unfortunately we are not supporting register-based drivers anymore, we are now using the HAL approach. So I won't be able to go investigate this issue further.
I'll add the ADC to our list of upgrades with the HAL, but if anyone on the community wants to take this on, please feel free.

[acassis]

@fdcavalcanti maybe @nuttxs could take a look, he added this driver.

As I remember the idea was to keep Xtensa as proper driver and new RISC (ESP32-C3/C6, etc) will use the HAL.

[shizacat]

@fdcavalcanti Thank you!