ESP32 i2s_read returns empty buffer after calling this function - c++

Question

I am trying to record audio from an INMP441 which is connected to a ESP32 but returning the buffer containing the bytes the microphone read always leads to something which is NULL.
The code for setting up i2s and the microphone is this:
// i2s config
const i2s_config_t i2s_config = {
.mode = i2s_mode_t(I2S_MODE_MASTER | I2S_MODE_RX), // receive
.sample_rate = SAMPLE_RATE, // 44100 (44,1KHz)
.bits_per_sample = I2S_BITS_PER_SAMPLE_32BIT, // 32 bits per sample
.channel_format = I2S_CHANNEL_FMT_ONLY_LEFT, // use right channel
.communication_format = i2s_comm_format_t(I2S_COMM_FORMAT_I2S | I2S_COMM_FORMAT_I2S_MSB),
.intr_alloc_flags = ESP_INTR_FLAG_LEVEL1, // interrupt level 1
.dma_buf_count = 64, // number of buffers
.dma_buf_len = SAMPLES_PER_BUFFER}; // 512
// pin config
const i2s_pin_config_t pin_config = {
.bck_io_num = gpio_sck, // serial clock, sck (gpio 33)
.ws_io_num = gpio_ws, // word select, ws (gpio 32)
.data_out_num = I2S_PIN_NO_CHANGE, // only used for speakers
.data_in_num = gpio_sd // serial data, sd (gpio 34)
};
// config i2s driver and pins
// fct must be called before any read/write
esp_err_t err = i2s_driver_install(I2S_PORT, &i2s_config, 0, NULL);
if (err != ESP_OK)
{
Serial.printf("Failed installing the driver: %d\n", err);
}
err = i2s_set_pin(I2S_PORT, &pin_config);
if (err != ESP_OK)
{
Serial.printf("Failed setting pin: %d\n", err);
}
Serial.println("I2S driver installed! :-)");
Setting up the i2s stuff is no problem at all. The tricky part for me is reading from the i2s:
// 44KHz * Byte per sample * time in seconds = total size in bytes
const size_t recordSize = (SAMPLE_RATE * I2S_BITS_PER_SAMPLE_32BIT / 8) * recordTime; //recordTime = 5s
// size in bytes
size_t totalReadSize = 0;
// 32 bits per sample set in config * 1024 samples per buffers = total bits per buffer
char *samples = (char *)calloc(totalBitsPerBuffer, sizeof(char));
// number of bytes read
size_t bytesRead;
Serial.println("Start recording...");
// read until wanted size is reached
while (totalReadSize < recordSize)
{
// read to buffer
esp_err_t err = i2s_read(I2S_PORT, (void *)samples, totalBitsPerBuffer, &bytesRead, portMAX_DELAY);
// check if error occurd, if so stop recording
if (err != ESP_OK)
{
Serial.println("Error while recording!");
break;
}
// check if bytes read works → yes
/*
for (int i = 0; i < bytesRead; i++)
{
uint8_t sample = (uint8_t) samples[i];
Serial.print(sample);
} */
// add read size to total read size
totalReadSize += bytesRead;
// Serial.printf("Currently recorded %d%% \n", totalReadSize * 100 / recordSize);
}
// convert bytes to mb
double_t totalReadSizeMB = (double_t)totalReadSize / 1e+6;
Serial.printf("Total read size: %fMb\n", totalReadSizeMB);
Serial.println("Samples deref");
Serial.println(*samples);
Serial.println("Samples");
Serial.println(samples);
return samples;
Using this code leads to the following output:
I2S driver installed! :-)
Start recording...
Total read size: 0.884736Mb
Samples deref
␀
Samples
When I uncomment the part where I iterate over the bytes read part I get something like this:
200224231255255224210022418725525522493000902552550238002241392542552241520020425225508050021624525501286700194120022461104022421711102242271030018010402242510000188970224141930022291022410185022487830021679001127500967200666902241776600246610224895902244757022418353002224802242274302249741022419339009435001223102242432602243322022412120001241402245911022418580084402248325525522461252255044249255224312452552242212372552241272352550342302552241212262552242112212550252216255014621325501682092550112205255224161202255224237198255224235194255224231922552248518725501141832550421812552241951762550144172255018168255034164255224173157255018215525522455152255028148255021014425505214025522487137255014613225522412112825502361252550180120255018011725522451172550252113255224133111255061082550248105255224891042552249910125522439972550138942552242279225503287255224101832552242478125522410178255224231732552244970255224336525501766225501426125502325625522424553255224109492550186[...]
This shows that the microphone is able to record, but I cant return the actual value of the buffer.
While programming this code I looked up at the official doku and some code which seems to work elsewhere.
I am also new to C++ and am not used to work with pointers.
Does anyone know what the problem could be?