Trouble playing WAV on ESP32 using I2S with internal DAC

[tim23x]

I'm trying to use I2S and internal DAC to play WAV files from SPIFF on a Heltec WiFi LoRa 32 V2, using the Arduino IDE.

I have an audio amp and an oscilloscope hooked up to DAC2 (pin 25) of the board and I'm not getting any signal. I've simplified the problem by generating a sine wave (as in the ESP-IDF examples). Here's the code:

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1. #include <Streaming.h>
2. #include <driver/i2s.h>
3. #include "freertos/queue.h"
4.  
5. #define SAMPLE_RATE     (22050)
6. #define SAMPLE_SIZE     4000
7. #define PI              (3.14159265)
8. #define I2S_BCK_IO      (GPIO_NUM_26)
9. #define I2S_WS_IO       (GPIO_NUM_25)
10. #define I2S_DO_IO       (GPIO_NUM_22)
11. #define I2S_DI_IO       (-1)
12.  
13.  
14. size_t i2s_bytes_write = 0;
15. static const int i2s_num = 0;
16.  
17. int sample_data[SAMPLE_SIZE];
18.  
19. i2s_config_t i2s_config = {
20.     .mode = (i2s_mode_t)(I2S_MODE_MASTER | I2S_MODE_TX | I2S_MODE_DAC_BUILT_IN),                                  // Only TX
21.     .sample_rate = SAMPLE_RATE,
22.     .bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT,
23.     .channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,                           //2-channels
24.     .communication_format = (i2s_comm_format_t)I2S_COMM_FORMAT_I2S,
25.     .intr_alloc_flags = 0,//ESP_INTR_FLAG_LEVEL1  
26.     .dma_buf_count = 8,
27.     .dma_buf_len = 64,
28.     .use_apll = false                           //Interrupt level 1
29. };
30.  
31. i2s_pin_config_t pin_config = {
32.     .bck_io_num = I2S_BCK_IO,
33.     .ws_io_num = I2S_WS_IO,
34.     .data_out_num = I2S_DO_IO,
35.     .data_in_num = I2S_DI_IO                                               //Not used
36. };
37.  
38. static void setup_sine_wave()
39. {
40.     unsigned int i;
41.     int sample_val;
42.     double sin_float;
43.     size_t i2s_bytes_write = 0;
44.  
45.     for (i = 0; i < SAMPLE_SIZE; i++)
46.     {
47.         sin_float = sin(i * PI / 180.0);
48.         sin_float *= 127;
49.         sample_val = (uint8_t)sin_float;
50.         sample_data[i] = sample_val;
51.         Serial << sample_data[i] << ",";
52.         delay(1);
53.     }
54.     Serial << endl << "Sine wave generation complete" << endl;
55. }
56.  
57. void setup() {
58.     pinMode(26, OUTPUT);
59.     Serial.begin(115200);
60.     i2s_driver_install(I2S_NUM_0, &i2s_config, 0, NULL);
61.     //i2s_set_pin(I2S_NUM_0, NULL);
62.     i2s_set_pin(I2S_NUM_0, &pin_config);
63.     i2s_set_dac_mode(I2S_DAC_CHANNEL_RIGHT_EN);
64.     i2s_set_sample_rates(I2S_NUM_0, 22050); //set sample rates
65.     setup_sine_wave();
66.     i2s_set_clk(I2S_NUM_0, SAMPLE_RATE, I2S_BITS_PER_SAMPLE_16BIT, I2S_CHANNEL_MONO);
67.     i2s_write(I2S_NUM_0, &sample_data, SAMPLE_SIZE, &i2s_bytes_write, 500);
68.     i2s_driver_uninstall(I2S_NUM_0); //stop & destroy i2s driver
69. }
70.  
71. void loop()
72. {
73.     i2s_driver_install(I2S_NUM_0, &i2s_config, 0, NULL);
74.     i2s_write(I2S_NUM_0, &sample_data, SAMPLE_SIZE, &i2s_bytes_write, 500);
75.     delay(100);
76.     i2s_driver_uninstall(I2S_NUM_0);
77.     delay(10);
78. }

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The code uploads and runs OK but I still get no signal on pin 25. I also looked on pin 26 (DAC1) but that seems to be used by LoRa_IRQ. Can anyone help me out?