ADC Digi First-Order IIR Filter is Missing from V5.0 (IDFGH-9113)

[willz1200]

Answers checklist.

• I have read the documentation ESP-IDF Programming Guide and the issue is not addressed there.
• I have updated my IDF branch (master or release) to the latest version and checked that the issue is present there.
• I have searched the issue tracker for a similar issue and not found a similar issue.

General issue report

I've recently made the transition to esp-idf v5.0 and have noticed that functions such as adc_digi_filter_set_config() and adc_digi_filter_enable() have been removed now the v4.4 legacy adc driver is depreciated.

ADC IIR functions were previously available here but haven't been kept around in v5.0. This breaking change also appears to be missing from the v4.4 to v5.0 migration guide. The back end HAL functions such as adc_ll_digi_filter_set_factor still appear to be present in v5.0 here, but obviously the HAL isn't considered a stable API so this wouldn't be a long term solution.

I could do with getting the IIR filter enabled to help compensate for the ESP32-S2's known poor ADC performance. Are there any plans to add the ADC IIR filter functions into v5.0?

[willz1200]

I've enabled the ADC IIR filter using code as follows

#include "hal/adc_ll.h"
#include "hal/adc_types_private.h"

adc_ll_digi_filter_set_factor(ADC_UNIT_2, ADC_DIGI_FILTER_IIR_2);
adc_ll_digi_filter_enable(ADC_UNIT_2, true);

My application uses the adc_continuous driver sampling 3 channels at 20kHz, with 10nF decoupling for each adc pin. The data is streamed out over UDP for analysis. When switching on the IIR filter, the data clearly gets much worse, eventually containing many repeating blips in the ADC reading. Am I correct in think the IIR filter has been left out of v5.0 because the hardware doesn't function as intended? Or am I missing something in my implementation?

ADC_DIGI_FILTER_IIR Turn Off

ADC_DIGI_FILTER_IIR_2

ADC_DIGI_FILTER_IIR_4

ADC_DIGI_FILTER_IIR_8

ADC_DIGI_FILTER_IIR_16

ADC_DIGI_FILTER_IIR_64

[Icarus113]

Hi @willz1200 , sorry for the migration guide lacking for these filter related APIs.

The filter related APIs were added in previous IDF versions, but the API behaviours were not guaranteed.
This feature is planned as a IDF v5.1 feature. We will add the lacking migration guide later.