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ULP ADC read fails #11599

ayavilevich started this conversation in Question - Community Help
Jul 6, 2025 · 6 comments · 11 replies
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Board

ESP32 generic dev module

Device Description

ESP32 generic dev module. Nothing additional connected.

Hardware Configuration

Nothing additional connected.

Version

latest stable Release (if not listed below)

IDE Name

Arduino IDE 2.3.6 and Platform.IO on VSC

Operating System

Windows 10

Flash frequency

40MHz

PSRAM enabled

no

Upload speed

921600

Description

Since Arduino-ESP32 2.0.14, using an ADC read operation in ESP32 ULP FSM co processor will cause the ULP to get "stuck".

I am including minimal code to reproduce.

Expected: wake due to an ULP wake after 5 seconds.
Actual: wakes due to (a fallback) timer wake after 20 seconds.

If using this code with ESP-IDF directly then it works as expected.
If using this code in a version before 2.0.14, then it works as expected.
If disabling the ADC read operation in the ULP code, then it works as expected.

More details at https://github.com/ayavilevich/ulp_adc_issue_ard_min/blob/main/README.md

Sketch

https://github.com/ayavilevich/ulp_adc_issue_ard_min/blob/main/src/main.cpp
Above can can be used with Arduino IDE, PIO or ESP-IDF.

Debug Message

Output, Arduino ESP32 3.2.0
ets Jul 29 2019 12:21:46
rst:0x1 (POWERON_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:1
load:0x3fff0030,len:4888
load:0x40078000,len:16516
load:0x40080400,len:4
load:0x40080404,len:3476
entry 0x400805b4
ESP-IDF: 5.4.1, ESP Arduino: 3.2.0
Start
Chip revision: 301
Not ULP/timer wakeup
TEST: sleeping for 20 sec
Entering deep sleep
ets Jul 29 2019 12:21:46
rst:0x5 (DEEPSLEEP_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:1
load:0x3fff0030,len:4888
load:0x40078000,len:16516
load:0x40080400,len:4
load:0x40080404,len:3476
entry 0x400805b4
ESP-IDF: 5.4.1, ESP Arduino: 3.2.0
Start
Chip revision: 301
Timer wakeup
Deep sleep wakeup
ULP do adc 1
ULP start counter: 2
ULP wake counter: 2
TEST: sleeping for 20 sec
Entering deep sleep
Output, Arduino ESP32 3.2.0 with ADC read disabled
ets Jul 29 2019 12:21:46
rst:0x1 (POWERON_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:1
load:0x3fff0030,len:4888
load:0x40078000,len:16516
load:0x40080400,len:4
load:0x40080404,len:3476
entry 0x400805b4
ESP-IDF: 5.4.1, ESP Arduino: 3.2.0
Start
Chip revision: 301
Not ULP/timer wakeup
TEST: sleeping for 20 sec
Entering deep sleep
ets Jul 29 2019 12:21:46
rst:0x5 (DEEPSLEEP_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:1
load:0x3fff0030,len:4888
load:0x40078000,len:16516
load:0x40080400,len:4
load:0x40080404,len:3476
entry 0x400805b4
ESP-IDF: 5.4.1, ESP Arduino: 3.2.0
Start
Chip revision: 301
ULP wakeup
Deep sleep wakeup
ULP do adc 0
ULP start counter: 51
ULP wake counter: 50
TEST: sleeping for 20 sec
Entering deep sleep
Output, ESP-IDF 4.4.6
ets Jul 29 2019 12:21:46
rst:0x1 (POWERON_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:2
load:0x3fff0030,len:5484
ho 0 tail 12 room 4
load:0x40078000,len:14824
ho 0 tail 12 room 4
load:0x40080400,len:3460
0x40080400: _init at ??:?
entry 0x40080638
ESP-IDF: 4.4.6
Start
Chip revision: 3, full: 301
Not ULP/timer wakeup
TEST: sleeping for 20 sec
Entering deep sleep
ets Jul 29 2019 12:21:46
rst:0x5 (DEEPSLEEP_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:2
load:0x3fff0030,len:5484
ho 0 tail 12 room 4
load:0x40078000,len:14824
ho 0 tail 12 room 4
load:0x40080400,len:3460
0x40080400: _init at ??:?
entry 0x40080638
ESP-IDF: 4.4.6
Start
Chip revision: 3, full: 301
ULP wakeup
Deep sleep wakeup
ULP do adc 1
ULP start counter: 51
ULP wake counter: 50
TEST: sleeping for 20 sec
Entering deep sleep

Other Steps to Reproduce

also tried on another ESP32 board. it made no difference.

I have checked existing issues, online documentation and the Troubleshooting Guide

  • I confirm I have checked existing issues, online documentation and Troubleshooting guide.
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Replies: 6 comments 11 replies

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To clarify, the indication of the ULP getting "stuck" is that the "start" and "wake" counters are not increasing as expected. See them getting the value of 2 at the point the device woke due to a timer. So just 2 invocations of the ULP program in 20 seconds.
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I don't see the settings ulp_low_thr = 1500; ulp_high_thr = 2000 in your code.
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I don't see the settings ulp_low_thr = 1500; ulp_high_thr = 2000 in your code.

There are no such settings in this project. You are probably confusing this with the "ulp_adc" example in ESP-IDF SDK.
examples/system/ulp/ulp_fsm/ulp_adc/main/ulp_adc_example_main.c

This POC is somewhat based on that code but the ULP program is different. It is ULP MACROs instead of ULP assembly, so there are no "c variables". You have 4 settings in RTC_SLOW_MEM. See:

#define U_MEM_START_COUNTER 0 // use as index to RTC_SLOW_MEM
#define U_MEM_WAKEUP_COUNTER 1
#define U_MEM_WAKEUP_COUNTER_GOAL 2
#define U_MEM_DO_ADC 3

I couldn't find a way to run the ESP-IDF ulp_adc example as-is on Arduino.
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I do understand this but the values 1500 and 2000 are nowhere applied in your code. I think the are needed, because the are there in IDF example.
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Those thresholds are used in another project where the ULP code compares the ADC reading with the thresholds. In the POC of this issue the value of the ADC is not used nor compared with anything.

This reproduce code is a different ulp program than the one in ulp_adc.
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@ayavilevich - This is not an Arduino issue. It is about ULP ASM and how to implement a specific project. I'll move it to discussion.

I think that the ULP has never completed running the ASM code.
It seems to miss esp_sleep_pd_config(ESP_PD_DOMAIN_RTC_PERIPH, ESP_PD_OPTION_ON); in order to define how the power domain for the ULP will behave when the ESP32 goes into deep sleep. By default, when the ESP32 deep sleeps, the ULP is not powered.

But I didn't try out the project, just took a quick look.
ULP will run at about 8MHz. It is slow. The ULP is started and right after that the ESP32 goes into deep sleep, which may stop the ULP automatically.

You can check this example from Arduino to see how the ESP32 ULP is used (maybe already done it?)
https://github.com/espressif/arduino-esp32/blob/master/libraries/ESP32/examples/DeepSleep/SmoothBlink_ULP_Code/SmoothBlink_ULP_Code.ino

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11 replies
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Were you able to discover anything?
Should this be converted back to an issue now that it was confirmed?
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I was out on vacation last 2 weeks. I couldn't find anything obvious.
I'll resume this investigation starting next Monday, 11th
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There is no clear change/commit fom one IDF version to another that can justify this problem.
This is an IDF issue. Converting it back to Arduino Issue won't help.

The best way to address it would be to create a pure IDF code that can be used by IDF team to identify why moving from IDF 4.4.5 to IDF 4.4.6 cause this probem. It would also confirm that the issue is in the IDF side.
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There is no clear change/commit fom one IDF version to another that can justify this problem. This is an IDF issue. Converting it back to Arduino Issue won't help.

The best way to address it would be to create a pure IDF code that can be used by IDF team to identify why moving from IDF 4.4.5 to IDF 4.4.6 cause this probem. It would also confirm that the issue is in the IDF side.

The code sample that I have provided
https://github.com/ayavilevich/ulp_adc_issue_ard_min/blob/main/src/main.cpp
is also valid ESP-IDF code. Just comment out the Arduino.h include.

I have tested the code with pure ESP-IDF (4.4.5 and 4.4.6) and the issue doesn't happen!
Please try to reproduce to confirm.
So it seems to me (based on tests) that this is triggered by Arduino-ESP32 somehow.
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Thanks @ayavilevich - I'll work on the code you have provided.
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Labels
Type: Question Only question Area: Peripherals API Relates to peripheral's APIs. Status: Community help needed Issue need help from any member from the Community.
Converted from issue

This discussion was converted from issue #11557 on July 15, 2025 13:15.

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