Problem with volume control using MAX98357A and I2S on an ESP32

[billys7]

I use the following code to reproduce an audio file with ESP32 --> I2S --> MAX98357A with success.

I want to add a software volume, so i add the code in comments. When i uncomment this part of the code the result is very noisy.
Do you have any suggestions ?

Code: [Select all] [Expand/Collapse]

1. #include "driver/i2s.h"
2. #include "freertos/queue.h"
3. #include <pgmspace.h>
4.  
5. #include "soundsample.h"
6.  
7. uint16_t readData1, readData2;
8. uint32_t readData, counter;
9.  
10. //i2s configuration
11. const int i2s_num = 0;                                                                  
12.  
13. i2s_config_t i2s_config = {
14.   .mode = (i2s_mode_t)(I2S_MODE_MASTER | I2S_MODE_TX),
15.   .sample_rate = 16000,                                                                
16.   .bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT,                                        
17.   .channel_format = I2S_CHANNEL_FMT_ONLY_LEFT,
18.   .communication_format = (i2s_comm_format_t)(I2S_COMM_FORMAT_STAND_I2S),
19.   .intr_alloc_flags = ESP_INTR_FLAG_LEVEL1,                                          
20.   .dma_buf_count = 8,                                                                  
21.   .dma_buf_len = 1024,                                                                  
22.   .use_apll = 0,
23.   .tx_desc_auto_clear = true
24. };
25.  
26.  
27. i2s_pin_config_t pin_config = {
28.   .bck_io_num = 26,                         //this is BCK pin
29.   .ws_io_num = 25,                          // this is LRCK pin
30.   .data_out_num = 22,                     // this is DATA output pin
31.   .data_in_num = I2S_PIN_NO_CHANGE        
32. //  .data_in_num = -1                      //Not used
33. };
34.  
35. int i2s_write_sample_nb(uint32_t sample)
36. {
37.     size_t bytes_written;
38.     i2s_write((i2s_port_t)i2s_num, (const char*)&sample, sizeof(uint32_t), &bytes_written, 100);  
39.     return bytes_written;
40. }
41.  
42. //Main function to play samples from PROGMEM
43. void playPROGMEMsample(const uint32_t* audioSample)
44. {
45.   i2s_driver_install((i2s_port_t)i2s_num, &i2s_config, 0, NULL);    //initialize i2s with configurations above
46.   i2s_set_pin((i2s_port_t)i2s_num, &pin_config);                          //initialize i2s with configurations above
47.   i2s_set_sample_rates((i2s_port_t)i2s_num, 16000);                    //set sample rates of i2s to sample rate of wav file
48.                                                  
49.   while (audioSample)  
50.       {
51.         readData = pgm_read_dword(&audioSample[counter++]);        
52.  
53. readData = ((readData>>24)&0xff) |   // move byte 3 to byte 0       // Convert big endian to little endian in C
54.            ((readData<<8)&0xff0000) |     // move byte 1 to byte 2
55.            ((readData>>8)&0xff00) |         // move byte 2 to byte 1
56.            ((readData<<24)&0xff000000); // byte 0 to byte 3
57.  
58. /*   Code for volume test
59. readData1 = uint16_t(readData>>16);
60. readData1 = readData1 /3;
61. readData2 = uint16_t(readData);
62. readData2 = readData2 /3;
63. readData = uint32_t (readData1 << 16)+ readData2;
64. */
65.  
66.         i2s_write_sample_nb(readData);
67.         if(counter > 125252) break;
68.       }
69.   counter = 0;
70.   readData = 0;
71.   i2s_driver_uninstall((i2s_port_t)i2s_num);                        //stop & destroy i2s driver
72. }
73.  
74. void setup()
75. {
76.   Serial.begin(115200);
77.   Serial.println("Serial connection OK");
78.   playPROGMEMsample(sample1);
79.    Serial.println("End");
80. }
81.  
82. void loop()
83. {
84.  
85. }

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[imanpakii]

Hello,

Did you Fix the problem?
I'm using driver/i2s.h and I would like to change the sound volume also.
Please give me your solution if you have it.

Thank you
Iman

[billys7]

I have no solution yet. I think that i must include the i2s_write function in an interrupt - task, so i can use it, only when the buffer will be empty. I read in this forum that i can trigger an event when the buffer is empty but i couldn't understand it. i want to learn more about the function :

"i2s_driver_install(I2S_NUM_0, &i2s_config, 0, NULL);"

i2s_num I2S device number
i2s_config I2S configurations - see i2s_config_t struct
queue_size I2S event queue size/depth. (what does that mean ? How can i know the value ?)
i2s_queue I2S event queue handle, if set NULL, driver will not use an event queue. (When the event will happend ?)

and especially about the last 2 parameters, and the way that i will do the interrupt - task.

Also, in the technical reference, i found the I2S_TX_REMPTY_INT interrupt. It is triggered when the transmit FIFO is empty. I think that this is what i am looking for, but i don't know how can i trigger it.

Unfortunately it is very difficult to find a guide, and the infos are limited.