esp32s3 ADC filter not working

[fallafenflufen]

Is anyone successfully using the ADC filters on the esp32s3?
I supply a constant voltage to an input pin (GPIO 8 - ADC0) and measure the same standard deviation of the converted ADC values regardless of the filter setting (0/1/2/3/4/off). I am using the continuous mode driver. The conversion values are OK, except the measured fluctuation is always the same.
I expect to see a reduction in standard deviation with filter enabled and with increased filter length.

Here is my configuration code:

Code: Select all

bool startADC()
{
  constexpr int BLOCK_SIZE = 256;
  constexpr float m_controlFrequency  = 100;
  constexpr gpio_num_t pin = GPIO_NUM_8;

    adc_continuous_handle_cfg_t adc_config = {
        .max_store_buf_size = (uint32_t)BLOCK_SIZE  * SOC_ADC_DIGI_DATA_BYTES_PER_CONV,
        .conv_frame_size = (uint32_t) BLOCK_SIZE  * SOC_ADC_DIGI_DATA_BYTES_PER_CONV,
    };
    ESP_ERROR_CHECK(adc_continuous_new_handle(&adc_config, &m_adcHandle));

    int adcSamplingFrequency = m_controlFrequency * BLOCK_SIZE ;

    adc_continuous_config_t dig_cfg = {
        .sample_freq_hz = (uint32_t) adcSamplingFrequency,
        .conv_mode = ADC_CONV_SINGLE_UNIT_1,
        .format = ADC_DIGI_OUTPUT_FORMAT_TYPE2,
    };

    adc_unit_t adcUnit;
    adc_channel_t channel;
    adc_continuous_io_to_channel(pin, &adcUnit, &channel);

    adc_digi_pattern_config_t adc_pattern[1] = {};
    dig_cfg.pattern_num = 1;
    adc_pattern[0].atten = adc_atten_t::ADC_ATTEN_DB_0;
    adc_pattern[0].channel = channel;
    adc_pattern[0].unit = adcUnit;
    adc_pattern[0].bit_width = SOC_ADC_DIGI_MAX_BITWIDTH;

    dig_cfg.adc_pattern = adc_pattern;
    ESP_ERROR_CHECK(adc_continuous_config(m_adcHandle, &dig_cfg));


    adc_continuous_iir_filter_config_t filterCfg = {
        .unit = adcUnit,
        .channel = channel,
        .coeff = adc_digi_iir_filter_coeff_t::ADC_DIGI_IIR_FILTER_COEFF_64 // or other values (0-4 integer values)
    };

    adc_new_continuous_iir_filter(m_adcHandle, &filterCfg, &m_adcFilterHandle);
    adc_continuous_iir_filter_enable(m_adcFilterHandle);
    // adc_continuous_iir_filter_disable(m_adcFilterHandle);  // for comparison test

    ESP_ERROR_CHECK(adc_continuous_start(m_adcHandle));

    return true;
}

[MicroController]

Any errors returned from the IIR functions?

[fallafenflufen]

While the code does not show any error checking, I checked the relevant IIR functions and all of them would print an error log, if there was an error. There is no error log output.