Is there anything to do to make the adc2_vref_to_gpio () function work?

[jhmluna]

Hello.
I am testing some ESP32 modules using VSCode + PlatformIO in Arduino framework.
My experiment involves putting some values in the output of DAC2 (GPIO26) and reading that value with ADC1_CHANNEL_6 (GPIO34).
My output values on DAC2 are updated via serial, transmitting values between 0 and 255.
The part that is puzzling me is related to the adc2_vref_to_gpio () function;
I'm using it this way:

Code: [Select all] [Expand/Collapse]

1.  // Routing ADC reference voltage to GPIO, so it can be manually measured (for Default Vref):
2.     esp_err_t status = adc2_vref_to_gpio(GPIO_NUM_25);
3.     if (status == ESP_OK)
4.     {
5.         printf("v_ref routed to GPIO25\n");
6.     }
7.     else
8.     {
9.         printf("failed to route v_ref\n");
10.     }

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I have already programmed three ESP32 modules using GPIO_NUM_26 and GPIO_NUM_27 as a parameter of the adc2_vref_to_gpio () function and in neither case did it work.
My question is whether I need to do anything else for the adc2_vref_to_gpio function to work.
I already tested it with an example of the ESP-IDF framework and it worked, I can read the reference voltage on the pin for the GPIO25, but if I use this function in the Arduino Framework, no GPIO produces the reference voltage.
Can someone help me?

The complete code is below.

Code: [Select all] [Expand/Collapse]

1. #include <Arduino.h>
2. #include <esp_adc_cal.h>
3. #include <esp_efuse.h>
4.  
5. #define DEFAULT_VREF 1100 // Use adc2_vref_to_gpio() to obtain a better estimate
6. #define NO_OF_SAMPLES 1  // Multisampling
7.  
8.  
9. static esp_adc_cal_characteristics_t *adc_chars;
10. static const adc1_channel_t channel = ADC1_CHANNEL_6; //GPIO34 if ADC1, GPIO14 if ADC2
11. static const adc_bits_width_t width = ADC_WIDTH_BIT_12;
12. static const adc_atten_t atten = ADC_ATTEN_DB_11;
13. static const adc_unit_t unit = ADC_UNIT_1;
14.  
15. static void check_efuse(void)
16. {
17.     //Check if TP is burned into eFuse
18.     if (esp_adc_cal_check_efuse(ESP_ADC_CAL_VAL_EFUSE_TP) == ESP_OK)
19.     {
20.         printf("eFuse Two Point: Supported\n");
21.     }
22.     else
23.     {
24.         printf("eFuse Two Point: NOT supported\n");
25.     }
26.     //Check Vref is burned into eFuse
27.     if (esp_adc_cal_check_efuse(ESP_ADC_CAL_VAL_EFUSE_VREF) == ESP_OK)
28.     {
29.         printf("eFuse Vref: Supported\n");
30.     }
31.     else
32.     {
33.         printf("eFuse Vref: NOT supported\n");
34.     }
35.  
36.     uint8_t chip_ver = esp_efuse_get_chip_ver();
37.     printf("Chip version is: %d\n", chip_ver);
38.  
39. }
40.  
41. static void print_char_val_type(esp_adc_cal_value_t val_type)
42. {
43.     if (val_type == ESP_ADC_CAL_VAL_EFUSE_TP)
44.     {
45.         printf("Characterized using Two Point Value\n");
46.     }
47.     else if (val_type == ESP_ADC_CAL_VAL_EFUSE_VREF)
48.     {
49.         printf("Characterized using eFuse Vref\n");
50.     }
51.     else
52.     {
53.         printf("Characterized using Default Vref\n");
54.     }
55. }
56.  
57. void setup()
58. {  
59.     Serial.begin(115200);
60.  
61.     // Set GPIO High in order to measure HIGH value voltage.
62.     pinMode(GPIO_NUM_17, OUTPUT);
63.     digitalWrite(GPIO_NUM_17, HIGH);
64.  
65.     //Check if Two Point or Vref are burned into eFuse
66.     check_efuse();
67.  
68.     //Characterize ADC at particular atten
69.     adc_chars = (esp_adc_cal_characteristics_t *)calloc(1, sizeof(esp_adc_cal_characteristics_t));
70.     esp_adc_cal_value_t val_type = esp_adc_cal_characterize(unit, atten, width, DEFAULT_VREF, adc_chars);
71.     print_char_val_type(val_type);
72.  
73.     // Routing ADC reference voltage to GPIO, so it can be manually measured (for Default Vref):
74.     esp_err_t status = adc2_vref_to_gpio(GPIO_NUM_25);
75.     if (status == ESP_OK)
76.     {
77.         printf("v_ref routed to GPIO25\n");
78.     }
79.     else
80.     {
81.         printf("failed to route v_ref\n");
82.     }
83.  
84. }
85.  
86. void loop()
87. {
88.     uint32_t adc_reading = 0;
89.     static int16_t dac_counter = 0;
90.     uint32_t voltage = 0;
91.     int Buffer = 0;  // Serial buffer
92.  
93.  
94.     // Read serial input to update DAC value
95.     if(Serial.available() > 0)
96.     {
97.         Buffer =  Serial.parseInt();
98.         if ((Buffer < 0) || (Buffer > 255)){
99.             Serial.println("Input number is invalid.");
100.         }
101.         else{
102.             Serial.print("Number is: ");
103.             Serial.println(Buffer);
104.             dac_counter = Buffer;
105.         }
106.     }
107.  
108.     // write dac value
109.     dacWrite(GPIO_NUM_26, dac_counter);
110.  
111.    
112.     // Reading ADC value
113.     unsigned long adc_conv_time = micros();
114.     for (int i = 0; i < NO_OF_SAMPLES; i++)
115.         {
116.             adc_reading += analogRead(GPIO_NUM_34);
117.         }
118.     // Calcualate mean value
119.     unsigned long adc_conv_time1 = micros() - adc_conv_time;
120.     adc_reading /= NO_OF_SAMPLES;
121.     voltage = esp_adc_cal_raw_to_voltage(adc_reading, adc_chars);
122.     unsigned long adc_conv_time2 = micros() - adc_conv_time;
123.    
124.     // Print values
125.     Serial.print("DAC: ");
126.     Serial.print(dac_counter);
127.     Serial.print("  Raw voltage: ");
128.     Serial.print(adc_reading);
129.     Serial.print("  Voltage: ");
130.     Serial.print(voltage);
131.     Serial.print("  Time adc: ");
132.     Serial.print(adc_conv_time1);
133.     Serial.print("  Time calculus: ");
134.     Serial.println(adc_conv_time2);
135.    
136.     delay(1000);
137.  
138. }

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[lbernstone]

This code works for me, and gives me a pretty consistent reading at 1113mV.

Code: Select all

#include <driver/adc.h>
gpio_num_t ref_pin = (gpio_num_t) 25;
void setup() {adc2_vref_to_gpio(ref_pin);}
void loop() {}

[jhmluna]

This code works for me, and gives me a pretty consistent reading at 1113mV.

Code: Select all

#include <driver/adc.h>
gpio_num_t ref_pin = (gpio_num_t) 25;
void setup() {adc2_vref_to_gpio(ref_pin);}
void loop() {}

Hello.
It is basically the same code I used.
If I write only your code it works, but if I use the adc2_vref_to_gpio() function in the same way in my code, it will stop working.
So, I think there is some incompatibility between the adc2_vref_to_gpio() function and some of the resources that I am using. Perhaps ADC1 or DAC2. I dont know...

[lbernstone]

If you want a consistent voltage on the pin, calibrate during setup with the vref, then use the dac to recreate that signal.

[jhmluna]

Hello @lbernstone
Thank you for your attention.
As for my application, I was able to get around this problem, so it is no longer a problem for me.
However, I decided to post because I think this is a bug in the Arduino framework.
I hope someone from the Espressif development takes a look at the post and gives an opinion.

[bikerbill]

Hi, i was testing this too and i was able to run your code (thanks for posting, it helped educate me). I don't think this is a bug, if you add a 10sec delay after esp_err_t status = adc2_vref_to_gpio(GPIO_NUM_25) before you do anything else with the ADC2 then it works fine. i read my Vref as 1.115v. as you said, something later on in your code seems to be disturbing this setup but the function itself appears to work ok.
regards bikerbill.